Wanna be engine builders

[dvogtvpe]

Here's a good article on rings and the bore. I've always stated that a round straight bore is important for not only ring seal but overall engine life.
http://www.enginebuildermag.com/2011...ct-horsepower/

[rickx]

Very interesting article! It leads me to question Kohlers' ring end-gap specification of .010 - .020 inches for the K321 engine!
From the article: "End Gaps McKnight says the optimal end gap for a top compression ring is when you achieve the smallest gap without butting the ends of the ring together when the rings get hot. “A good starting point for the top compression ring is .0045? per inch of bore diameter for a naturally aspirated engine,"
The K-321 engine approximate piston diameter = 3.5 inches, 3.5X.0045= .016 inches end gap.
I gapped my rings at .011 -.012 on my recent rebuild job, Is this end gap too tight for an air cooled engine? Can't imagine a water cooled engine needing more end gap.

[austin8214]

You are in Kohler's spec do not worry about it. Your fine.

[dvogtvpe]

the article wasn't meant to reengineer the Kohler manual. for a stock engine always follow the given specs. We use allot of automotive stuff in our pulling engines forged pistons, moly rings, special cyl coatings this is where you have to pay special attention to detail. for probably 95% of the people on this forum there's no need to know any of the stuff in that article. My point was how critical bore is in ring life and ring seal and how it can affect an engine. I can't say it enough

[rickx]

Originally Posted by dvogtvpe

the article wasn't meant to reengineer the Kohler manual. for a stock engine always follow the given specs. We use allot of automotive stuff in our pulling engines forged pistons, moly rings, special cyl coatings this is where you have to pay special attention to detail. for probably 95% of the people on this forum there's no need to know any of the stuff in that article. My point was how critical bore is in ring life and ring seal and how it can affect an engine. I can't say it enough

Seeing as how many engines you have rebuilt, how often have you had to have a cylinder redone because of faulty machining? How closely do you check the bore on the cylinders you get back from the machine shop? Just curious, this engine tech is very interesting.

[austin8214]

Originally Posted by rickx

Seeing as how many engines you have rebuilt, how often have you had to have a cylinder redone because of faulty machining? How closely do you check the bore on the cylinders you get back from the machine shop? Just curious, this engine tech is very interesting.

I always check what comes back from the machine shop until I trust them. The current shop I use I don't have to check up on. They are always spot on.

[rickx]

Originally Posted by austin8214

You are in Kohler's spec do not worry about it. Your fine.

Thanks Austin,
Sounds good to me! But if I do another rebuild, I just may look into end gap recommendations of other cast iron air cooled engine manufacturers...