Full Engine Rebuild for 1959 Austin Healey Bugeye (Frogeye)




Introduction: Full Engine Rebuild for 1959 Austin Healey Bugeye (Frogeye)

About: I like building things mainly from wood or metal. Especially if they look complicated to make, then I like to think about how to make it. And I love it when the result looks good.

One of my friends owns a 1959 Austin Healey Sprite. (It is a little car with big headlights and therefore it is called Bugeye in the US or Frogeye in the UK.)

The car has not been used in the past year for several reasons and the engine was not in great condition anymore. It made strange noises when the engine was being started and when it was running it had blue smoke coming out of the tailpipe. When we first started working on the car, we were just considering to give it some basic maintenance, but one thing led to the next and very soon we decided that we would do a full engine rebuild to solve all issues and to get the Healey ready for many years to come.

Although the car is from 1959, the engine itself is younger. One of the previous owners had the original engine replaced by a more powerful 1275 cc engine from a Mini Cooper. There are still several reconditioned Mini Cooper engines on the market, so we figured that if we would totally fail in rebuilding the engine, we would have a back up option.

Rebuilding an engine is fun and we did a successful rebuild of another engine last year, so for this Bugeye engine rebuild we decided to document the entire process and share it with you. I do have to mention that we are not professional mechanics so maybe things can be done better, but we just share what we did, so you can learn from our experience and mistakes.

Step 1: Diagnostics

Taking an engine out of a car and rebuilding it is a lot of work, so it is important to decide if it is really needed to do this. We started with a compression test and a cylinder leak test to get an idea about the internal condition of the engine. These tests do require special measuring equipment, but it is not really expensive and my friend had these tools, so we could do the tests.

We started with a compression test: we took the spark plugs out, placed the instrument on the hole of the spark plug and turned the engine over and measured a low compression. We added some oil through the holes of the spark plugs and did the test again and still the compression was low, but the results for each cylinder were similar. What we did not know that day was that we also had to make sure the throttle valve was fully open, because air needs to flow freely into the engine before compression. Therefore the results of our compression test were not accurate.

But we did not yet know that and we continued with the leak test. We knew that the piston had to be on TDC (top dead center) during this test, so we checked that the piston was at it's highest point by feeling where it was through the hole of the spark plug and then we connected the meter to the hole of the spark plug, added the compressed air and looked at the results. It is a 4 cylinder engine so 2 pistons are at TDC at the same time, one with both valves closed and one with both valves open. Of course compressed air immediately leaks away if both valves are open, so the photo with 95% leakage is for the cylinder that has both valves open. The other photo is for the cylinder that is at the beginning of it's compression stroke and there the leakage is 50%, which is not great.

Now we had three issues: the blue smoke from the tail pipe, the result of the leak test and the noise when starting the engine, so we decided to go ahead taking the engine out.

Step 2: Getting the Engine Out of the Car

Getting the engine out of this car was quite easy as the engine bay of a classic car is not as full as for modern cars. Still each car is different, so it is not useful if I describe every nut and bolt that had to be loosened to get this engine out of this car. Therefore, I will give a bit more general description of how to get the engine out.

  • We removed the hood (or bonnet if you are from the UK). It was just connected with a few nuts and bolts.
  • We drained the coolant from the radiator and removed the radiator. With the coolant hoses disconnected, we could also see a lot of dirt in the cooling system, so another reason to continue with the overhaul of this engine.
  • We drained the oil from the engine.
  • We disconnected the air inlet and exhaust and we disconnected the prop shaft.
  • Finally we loosened the bolts for the engine support and used a hoist to lift the engine out together with the gear box.

Here are some tips:

  • Take many photos, so later it is easier to remember where all parts were that you took off.
  • Put the plug back after draining the oil. We did not do that, which resulted in more oil coming out when the engine was tilted to get it completely out of the engine bay.
  • Make sure to check if everything is disconnected while hoisting the engine up and out. We had one of us operating the hoist and the other one was looking under the car and in the engine bay to make sure nothing would be pulled loose. This went very well.
  • Make sure that the hoist is strong enough to be able to lift the engine.

It took us just 2 hours to get the engine out, but there are many cars where it can take longer to get this done.

Step 3: First Internal Inspection

First we removed the bolts that were used to attach the gear box to the engine, so the engine was much lighter and easier to handle. It also revealed the fly wheel and showed that the starter ring gear had a missing tooth. That explained the strange noises when we wanted to start the engine. It also meant we had to replace the starter ring gear.

We removed the valve cover and the bolts that kept the engine head in place. Then we removed the engine head to be able to get a first impression of the valves and pistons. And although it looks dirty, it did not show any big problems.

Some advice:

  • Be aware that when you remove the engine head, you will need at least a new head gasket, but it is also quite likely that the engine head is no longer completely flat and you need a machine shop to get the head completely flat again.
  • Take many, many photos to keep track of where all parts where. It is a bit of a struggle to handle a phone or camera when your hands are dirty from oil and grease, but without photos it is much harder to rebuild everything later.
  • Do not mix any parts that seem identical, like valves, pistons and rods, but keep them all in order. When you put the piston of cylinder 1 back in another cylinder the wear pattern of the piston does not match with that cylinder and you could end up with problems, so make sure you do not mix or rotate anything.
  • Avoid that any hard, sharp or abrasive particles can end up inside the engine, as that can result in engine damage later on. We placed the engine on a wooden table and used many rags to remove dirt.

Step 4: Further Disassembly

The timing of an engine is essential for it's proper operation, so it is very important to make sure that it is clear how the crack shaft and cam shaft are connected. In our engine there was a chain connected to two sprockets and the sprockets were connected to the shaft by a keyway. Both sprockets had a dot and both dots had to align to be sure that the sprockets were in the correct position. Here it is again very important to take photos and mark how parts were connected before removing them.

We also removed the clutch and decided that we were going to replace the friction plate also. The old one was not that bad, but since we were rebuilding the entire engine, we could as well make sure the clutch would be perfect again.

Step 5: Checking the Pistons

We cleaned a steel sheet and put it on the workbench and placed the parts in the same order as they had in the engine. Then we used a micrometer to measure the diameter of each piston and wrote down the results. The right location to measure the diameter of the piston is as shown on the photo, so at the bottom of the skirt and 90 degrees compared to the gudgeon pin.

Then we also measured the internal diameter of the cylinder to check the clearance between piston and bore. We measured all 4 cylinders on three depths so at the top, middle and bottom of the cylinder and we also measured in two directions so in line with the engine block and perpendicular to it. Our results were within 0.10 and 0.15 mm, which is high but not extremely high.

Step 6: Elbow Grease Which Could Have Been Avoided

Based on the results of our measurements we thought that replacing the pistons was not really needed, so we decided to clean them. The black oil and fuel residue is not that easy to remove, so we used a hydraulic press to remove the gudgeon pins from pistons, placed the pistons in an ultrasonic cleaner for about 15 minutes and then used WD40 and a lot of elbow grease to clean the pistons. The result looked much better, so we used the press to reassemble the pistons, gudgeon pins and connecting rods.

However, some days later we visited a specialist at a machine shop and based on the information we got there, we decided it was better to use new pistons, so we could get the right clearance between piston and bore and we could also select pistons for a slightly higher compression ratio, so the engine would get more power.

So all the cleaning could have been avoided and once again we used the press to separate the pistons from the connecting rods, because the connecting rods were going to be reused.

Step 7: Removing the Damaged Starter Ring Gear

We ordered and received a new starter ring gear to replace the one with the missing tooth. We tried to heat up the old ring to make it expand, but that did not work. The heat also goes into the flywheel so the flywheel heats up and expands too.

So I clamped the flywheel in the vise and used a grinder to make a slot. I could not get deep enough, so I used a drill to drill a hole in the corner where I could not get with the grinder. You can see on the photo that the stress in the metal already causes the remaining thin layer of metal to crack. I hit it with a hammer and chisel only once and it was even a very old chisel intended for wood, but that was all it needed and the ring snapped and the flywheel was not damaged.

Step 8: Placing the New Starter Ring Gear

To place the new starter ring gear, I brought out the torch again. This time it only had to heat up the ring, so that went well. It is enough to heat up the ring until it is a bit blue and then I picked it up with the pliers and it fell real easy over the flywheel. I did not need the hammer at all.

Make sure not to heat up the ring until it is red hot, because the teeth are hardened and if the teeth are heated up the heat could undo the hardening process, so then the teeth might wear out faster.

Step 9: Other Checks

While we dismantled the engine, we checked which parts we were going to reuse and which parts my friend was going to order new. As it was his car, he was of course the one paying for all the new parts, so I had all of the fun, but none of the costs :-)

The oil pump showed severe grooves on the cover plate, so it could no longer pump oil properly, so the oil pump definitely had to be replaced.

We used Plastigauge to check the clearance of all engine rod bearings and connecting rod bearings and actually the clearance was quite good. But since these bearings are not that expensive and the engine would already get new pistons, we decided to order also new bearings.

The water pump and thermostat housing were in bad condition, so they were going to be replaced by new ones.

The spark plugs look still acceptable and they can easily be replaced even when the engine is back in the car, so they were going to be reused.

Step 10: Ordering and Receiving Other New Parts

The engine that we were rebuilding is a quite common engine, so ordering parts should have been easy. We went to a parts store specialized in classic cars and they told us that is was no problem to order the parts that we needed. Unfortunately we did receive several parts that were not what we needed.

The oil filter was not delivered correctly as the size of the hole in the center is different, so the new oil filter did not fit and we had to get another one.

Also the new big end bearings were not delivered correctly. The ones we received are in my left hand and the old ones are in my right hand. The old ones have a groove in the middle and the new ones did not. Also the position of the dent that should match with the slot was not in the right place, so we could not use these and had to revert to the store.

Of course not all deliveries went wrong. For example the water pump on the photo was a perfect match. But the new timing chain and sprockets confused us. (We decided to order them new, because the chain and teeth of the old ones were a bit worn.) I assembled the new chain and sprockets and since timing is so important I compared the new ones against the old ones. As you can see on the photo, the keyways indicated by the yellow arrows are in a similar position, but the dots align for the old sprockets and they do not align for the new sprockets. It took me some time to realize that this does not matter. When I align the dots on the new sprockets the position of both keyways changes, but their relative position to each other does not change. Anyway, to be extra sure I added two dots with white paint on the new sprockets to show where the dots on the old sprockets were and we decided that the new sprockets were fine.

Step 11: Consult a Specialist

We took the engine to a specialist at a machine shop to ask his opinion about the results of all our measurements and about the pattern of the scratches in the cylinder.

I already wrote that the clearance between piston and bore was a bit too large. Also there were vertical grooves shown in the blue rectangle on the photo. If the grooves stayed there, the engine would continue to burn some oil and it would still have blue smoke from the tail pipe. The guy at the machine shop tried a quick honing with a kind of brush attached to a drill, but the grooves were too deep to disappear.

The best thing we could do was order pistons that where larger than normal and the machine shop would bore and hone the engine so we would get the perfect clearance and all grooves would be gone.

Step 12: Work Done at the Machine Shop

The machines needed for boring and honing an engine are that expensive and large that this step is not a DIY job. The guys at the machine shop did this for us and also they made sure the engine head was perfectly flat and the valves sealed well again.

Step 13: Checking the Results

When we received the engine back from the machine shop, the cross pattern from honing was clearly visible. This is important as it gives the oil something to adhere to while the new piston rings are still rough and not worn in to the bore.

Since piston to bore clearance is important and we had the tools we decided to check the clearance for the new pistons and the bore after the honing process. It is similar to what we did in step 5. We measured the skirt of the new piston with a micrometer. We used the micrometer to set 0 on the bore measuring tool and then placed the tool in the bore and measured the difference. That is the clearance we are looking for. We measured 0.065 mm while the minimum clearance for our pistons had to be 0.075 mm. If the clearance is too small there is a risk that a piston gets stuck in the engine and that would result in a damaged engine. So we took the cylinder block back to the machine shop, they agreed that our measurement was correct and they immediately honed the cylinder block again.

Step 14: Gap in the Piston Rings

It is important that the gap in the piston rings is around 0.35 mm when the piston rings are in the cylinder. The rings will expand when they heat up and then the gap is almost fully closed. If the gap is too narrow when everything is still ambient temperature, the rings cannot freely expand when they heat up and that can cause damage. If the gap in the piston rings is too wide, there will be additional blow by where fuel is blown into the crank case without being burned.

We tested the gap by placing one piston ring in the bore, using the piston to push the ring a bit further so it is not twisted and then we used a feeler gauge to check the gap. When the gap is too narrow, the ring can be taken out and one end of the ring can be filed. Filing for just 20 or 30 seconds per ring was already enough.

It is also important to make sure there are no burrs at the rings from filing. A burr will immediately make a groove in the bore, so check all rings for burrs.

Step 15: Placing New Rings on the Pistons

After adjusting the gap, we had to place the new rings around the pistons. There is a tool for this, but it takes a little bit of practice to get used to the tool, so we just placed the rings without the tool. It helps to place the piston on the vise without clamping it, so you have to hands available for the rings. I managed to break one ring, so we had to get a new one for that.

On the last two photos you see the new piston next to an old one. Because the new piston is for a higher compression ratio, the new ones are slightly higher and the top side also looks a bit different.

The red number 1 shows that was the old piston for cylinder 1. The number 71.51 is the size in mm of the new piston. When it is useful to write something on the piston, it is no problem at all to do that.

Step 16: Cleaning and Checking Everything

I cleaned every part and while doing that I checked if I could see any damage. Here you see me cleaning the clutch and checking the rubber around the bolt for the valve cover. My friend had to arrange a new rubber, because this one is damaged.

Step 17: Organizing All the Parts

Before the actual rebuild started, we arranged all parts to get a clear overview of what we had. Make sure to place the parts on a clean surface. There should not be any sharp or abrasive particles on the parts because they can end up in the engine.

Step 18: Some Details That Are Applicable for the Entire Rebuild

These photos are from some of the next steps, but they show some important details:

  • Make sure to add oil on every part that will be moving in the engine, so there is already some lubrication before the engine is started.
  • Replace all used lock rings by new ones. Lock rings are intended for single use only and we do not want anything to come loose because of an used lock ring.
  • Add copper grease or anti seize on all bolts that could get stuck by corrosion.
  • Use gaskets and/ or RTV on all parts where oil or coolant should not leak out.
  • Use a torque wrench to tighten all bolts in the required order and on the correct torque. Check documentation for the correct torque.

Step 19: Start Assembling

The next steps show the actual assembly during our rebuild.

We started by placing the cam followers that follow the cam shaft and transfer the movement to the rockers. These cam followers are oiled and then placed in their hole in the same order as they originally came out.

After that we could slide in the cam shaft from the side of the engine.

Step 20: Installing Bearings and Crank Shaft

We oiled all bearings, and put the crack shaft in place and placed the caps and tightened the bolts on the correct torque.

Step 21: Installing the Pistons

Since the piston rings make it difficult to slide the piston into the bore, we used a tool to compress the springs. Then we used the wooden end of a hammer to gently tap the piston completely in. At the crank shaft side we pulled the connecting rod towards the crank shaft.

Step 22: Checking the Connecting Rod Clearance

We used Plastigauge again to check the clearance in the bearings of the connecting rod. The way to do that is to cut a small piece of Plastigauge, which looks like a tiny bit of clay and place it on the bearing. Then we tightened the bearing cap at the required torque and loosened it again, making sure not to rotate any shaft. Then we compared the width of the compressed Plastigauge with the scale and here the value was fine. In general the clearance should be 0.1% of the diameter of the bearing.

Step 23: Rebuilding the Fly Wheel Side

Now we get to rebuilding the fly wheel side. An important thing to check was if the gear of the oil pump still has something to drive it. It is driven by a gear in the cam shaft, but that gear is a loose part and therefore it could have fallen out during all the cleaning and handling we did.

The oil pump gets a cover sealed by RTV and the crack shaft has an oil seal on the connection of the fly wheel.

Step 24: Installing Fly Wheel and Clutch

We placed the fly wheel on the crack shaft where the orange oil seal was on the photos of the previous steps. We tightened the bolts and made sure they cannot come loose by bending the metal sheet behind the bolts.

Then we made a little shaft on the lathe to keep the clutch plate centered while we installed the entire clutch.

Now this side of the engine is ready because we will connect the gear box later.

Step 25: Rebuilding the Timing Chain Side

On the other side we installed a plate and then both sprockets with the timing chain. We used the dots of white paint that I added in step 10 although indeed the other dots were also fine.

Then we checked the clearance of the cam shaft and it was perfect 0.10 mm.

The clearance of the crank shaft was also perfect: 0.08 mm.

If these side way clearances would have been to much, we could have added a spacer, but since the clearance was perfect, we did not have to correct anything.

Step 26: Bottom Side

At the bottom we bolted the oil pick up where it belonged and then we added the crank case, while we made sure the gasket was in place including some RTV.

Step 27: Cylinder Head

As last part of the rebuild we put the cylinder head back in place with a new gasket.

We installed the rockers and the head bolts and tightened them in the prescribed order and with the prescribed torque.

We temporary placed old spark plugs, so we could paint the engine without painting the good spark plugs.

We did not yet check the valve clearance as it was getting really late in the evening and we first wanted to give the engine a layer of paint that could dry during the night. Of course we will set the valve clearance before actually starting the engine.

Step 28: Preparation and Primer

We covered everything that should not be painted with tape or paper and then we used a spray can to add a primer. As you can see we opened the door, so fresh air could come in while we were spraying the primer.

Step 29: Painting

The next day we put the engine in a small crane so we could reach all sides and painted it green.

Step 30: Still Some Work to Be Done

After painting we added the fan and the carburetors and the engine looks great again.

The final step should be that we place the engine back in the car, but right now the car looks like you see on the photo. The Healey seems to smile, so I hope it is happy that it is also getting a full body respray.

We completely stripped the car and when it gets back from the paint shop we will rebuild it and after that we will put the engine back in the engine bay.

Before actually starting the engine, we will do a final round of checks:

We will pour some oil completely over all rockers and valves at the top side.

Then we will feel if the engine still can be turned quite easily by hand when the spark plugs are not in place.

Then we will turn the engine without the spark plugs and without the valve cover so the engine does not fire but we can check if the oil pump is working properly.

After that we will put the spark plugs back, make sure the valve clearance is fine, place the valve cover and then we will actually fire the engine.

If it runs we will check the timing with a lamp and the combustion with an analyzer.

With the previous engine this all worked fine so we are quite confident that the Healey will also run fine.

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    3 months ago on Step 30

    I hope you will keep up apprised of your progress


    3 months ago

    Nice job on documenting your rebuild, Just a tip next time you do a ring gear there is no need to heat or cut it, just a couple of wacks with a drift and a hammer and they will pop off with out any risk of damaging the flywheel


    3 months ago

    Your 1959 AH was built to run on leaded gasoline. The lead in the fuel actually lubricated the valve seats and reduced wear. This allowed the seats to be fabricated in the cast iron head. Now with unleaded fuels those cast iron seats do not last and you will be doing a another head job rather quickly. You have two solutions. One is to have a machine shop place steel valve seat inserts in the head. The other is to use an lead replacement additive. Your instructable ix sure better than you find in so called service manual published in the US.


    3 months ago on Step 30

    I bought a clapped out 1958 Bugeye in 1967 for $250 and made just about every possible mistake working on it. I had it bored .020 over but failed to clear all the honing abrasive out of the block so when I put it back into service the engine very quickly wore out. Sprites were known to have rather delicate power assemblies. A friend's Sprite had recurrent transmission troubles. Mine broke an axle while simply turning left in an intersection (at least it's so light it's easy to push). I didn't like that it was positive ground so I repolarized the generator to make it negative ground (that seemed to work OK) like is standard on American cars and usable with more readily available radios. The absolute worst thing I did was, noticing that the wires in the electrical system looked pretty bad, I removed the wiring harnesses for the entire electrical system and threw them all away. After they were gone I belatedly realized that, while I had complete schematics of the electrical system, knew what all the connections were, and where all the connections had to be made, I had no pattern for the dimensions and routing of the wires in the electrical system wire bundles. Finally somebody wanted the old undrivable Sprite's hulk badly enough to pay $800 for it in 1984. It was great fun while it ran and now, of course, I regret not having it. It's my understanding that only 60,000 Bugeyes were ever made so I hope whoever has one now is a lot smarter than I was.


    Reply 3 months ago

    Thanks for sharing your experiences. The positive ground is indeed something which feels odd. I also removed all the cables for the full body respray, but they do not look bad, so we plan to reuse them.
    I will probably make another Instructable about the restoration of the car itself when that is ready. Hopefully within a few months.


    Reply 3 months ago

    Should you become moved to rewire, disassembly of the old harness and paralleling new wires with the old is the way to do it. If I had it to do again I'd stretch out the old harness on a sheet of plywood with the wires, old and new, guided by strategic nails placed in the plywood as in the attached photo of a military aircraft harness board. That might also work for you while you have the harness out, should you decide to neatly add some wiring for something new like a USB power connector or something. Good luck and have fun.


    3 months ago

    Good article. I am a Diesel Mech and the 0.01mm tight on piston clearance for one of those engines would have done no harm. In fact when building go fast engines we often go on the tight side, run them and then pull down to see if there is any scuffing and just polish it out. That engine would never spin fast enough or get hot enough to break through a modern oil but yes the shop should have honed to spec - to each individual piston as well if you want to be fussy.
    I noticed the old water pump had a lot of corrosion like it had been run on plain water - VERBOTEN!
    The inside of the block will be clogged up as well. Run a water:Molasses mix at 40:1 by volume in the cooling system. This is safe to leave in for a month. Flush the cooling system twice after,(radiator separate so you can back-flush it), and then add your water/Glycol mix.
    I rebuild vintage stuff for a hobby and the above has saved many blocks. Works on modern cars as well.


    Reply 3 months ago

    Thanks for your advice. The engine block has been in a washing machine at the machine shop to clean it, so I assume the block itself should be clean?
    We should indeed flush the radiator and the rest of the cooling system.


    3 months ago

    This was really fun to see and read through. I appreciate you for taking the time to document and share this!

    An engine rebuild is something I've never seen in this kind of detail before - so I found this very, very interesting. Thank you!


    Reply 3 months ago

    Thank you. It is very nice to read all the comments, memories and additional advice from other people, so I am happy that I could share this Instructable.

    Prusa Fanatic
    Prusa Fanatic

    3 months ago

    I absolutely love mechanics and some day hope to do a full car restore. Maybe then this will come in handy :) if not before. Awesome job!! Thanks!


    Reply 3 months ago

    It is really fun to restore a car. I hope you will find a nice project and enjoy it.


    3 months ago

    OK, you have my deepest respect. I pulled the engine cradle off of my '98 Saturn SL1 in my driveway about 15 years ago. Never ever ever want to do that again. So an engine pull and rebuild just floors me. Good instructable.


    Reply 3 months ago

    Thank you very much


    3 months ago on Step 30

    Nothing short of a drop dead GREAT instructable. A complete rebuild in one handy usable package is not something easily found. There are more examples of this kind of rebuild than you might think. Your instructable is valid with minimum differences for Austin Healey Sprites from 1958 thru 1969 as well as MG Midgets from 1962 (I believe) thru 1969 They all used 948cc (1098cc for MG Midgets) thru 1075cc engines interchangeably. There are a lot of owners out there with these cars, now around the world that would attempt a rebuild if they only had a little more clarity to what was necessary. Now they do.


    Reply 3 months ago

    It would be great if someone would indeed attempt a rebuild based on our experiences. Thank you for your comments.


    3 months ago on Introduction

    Nice job! Worthy of auto SOS! Ah, such fond(?) memories of spending weekends trying to synchronize those twin SUs and "decoking" the heads. BTW - An A40 made a suitable block donor for a transplant (after the rebuild, of course).


    Reply 3 months ago

    Thank you