Print PDF
Favorite
Email
Step 14Porting and polishing the engine.
Porting and Polishing
The next step was to start working on the engine. The engine I got was a early 90's Briggs 14.5 OHV. There are a lot of similarities between it and the old 12.5 flathead I had. The crank, piston, rod, and carb in the 12.5 are basically the same. Thus I was able to scavenge the old magnesium piston and billet rod I'd been running. The rod is an ARC rod and has replaceable bearings. Its always important to replace these if you're sticking them in a new engine. I also ordered new rod bolts.
I'd also decided to try out a new product from ARC, which is a billet chrome molly billet crank. Just as I got started on the engine they came out with it. For years we've had a dilemma where the old heavy cast iron counterweights that came with these engines not only presented an issue of having to deal with more mass, but on occasion these have come loose, smashing through the crank case. The solution was to get an old-style 80's or early 90's crank with removable eccentrics and install lightweight brass counterweights. ARC developed a billet crank with the counterweights machined into the piece- thus its all one piece. I opted for this part.
Also ordered was a new set of valves and more "modern" valve keepers. The old style of keepers uses a sort of cap with a slot cut in the top. These have been known to come loose out on the track- causing damage to the head. The new keepers are similar to ones you'd find in a car and are highly unlikely to come loose.
Lastly, while I thought I would be able to re-use my old billet aluminum flywheel, the one I had was solid aluminum-including the hub. The hub was badly damaged from having slipped numerous times on the crank. I ordered an ARC billet flywheel with a removable steel hub- thus making it also adjustable. In doing so I also had to order a high-torque starter. The starter looks like something you'd find in a car also. Its made by Denso- the folks that make parts for Toyota.
Anyway, one way to increase engine performance is to do something called "porting and polishing". What this entails is to basically provide an easier way for gasses to enter and exit the engine. From the factory the intake and exhaust ports have rather sharp edges. Run your finger inside the area where the port enters the valve area and its almost sharp enough to cut you. These edges will need to be shaved down and smoothed over. I used a stone mounted to my Dremel tool to slowly cut and blend these areas so that the airflow would be smoother. I then followed up with some polishing compound and gave it a mirror polish. This took hours but its worth it in the end.
The next step was to start working on the engine. The engine I got was a early 90's Briggs 14.5 OHV. There are a lot of similarities between it and the old 12.5 flathead I had. The crank, piston, rod, and carb in the 12.5 are basically the same. Thus I was able to scavenge the old magnesium piston and billet rod I'd been running. The rod is an ARC rod and has replaceable bearings. Its always important to replace these if you're sticking them in a new engine. I also ordered new rod bolts.
I'd also decided to try out a new product from ARC, which is a billet chrome molly billet crank. Just as I got started on the engine they came out with it. For years we've had a dilemma where the old heavy cast iron counterweights that came with these engines not only presented an issue of having to deal with more mass, but on occasion these have come loose, smashing through the crank case. The solution was to get an old-style 80's or early 90's crank with removable eccentrics and install lightweight brass counterweights. ARC developed a billet crank with the counterweights machined into the piece- thus its all one piece. I opted for this part.
Also ordered was a new set of valves and more "modern" valve keepers. The old style of keepers uses a sort of cap with a slot cut in the top. These have been known to come loose out on the track- causing damage to the head. The new keepers are similar to ones you'd find in a car and are highly unlikely to come loose.
Lastly, while I thought I would be able to re-use my old billet aluminum flywheel, the one I had was solid aluminum-including the hub. The hub was badly damaged from having slipped numerous times on the crank. I ordered an ARC billet flywheel with a removable steel hub- thus making it also adjustable. In doing so I also had to order a high-torque starter. The starter looks like something you'd find in a car also. Its made by Denso- the folks that make parts for Toyota.
Anyway, one way to increase engine performance is to do something called "porting and polishing". What this entails is to basically provide an easier way for gasses to enter and exit the engine. From the factory the intake and exhaust ports have rather sharp edges. Run your finger inside the area where the port enters the valve area and its almost sharp enough to cut you. These edges will need to be shaved down and smoothed over. I used a stone mounted to my Dremel tool to slowly cut and blend these areas so that the airflow would be smoother. I then followed up with some polishing compound and gave it a mirror polish. This took hours but its worth it in the end.
| « Previous Step | Download PDFView All Steps | Next Step » |
 |
Add Comment
|
