Cylinder wall wear

[golden]

How smooth do the walls need to be? I have to replace a busted connecting rod and piston. There are some small grooves. How do I know what's too much?

 

[funpilot]

Re: Cylinder wall wear

Your best bet is to take the block to a shop who is familiar with machining aluminum blocks and marine engines in particular. The tolerances for roundness of the cylinder and piston are as important as how smooth the surface is. After your machine shop does its work, they will recommend the proper piston (oversize or not). As long as you have to replace a busted piston, might as well do it right. Check the head for smoothness as well, nicks can collect carbon, which can stick in a ring, which can cause another failure.

For example on my crossflow 90, two cylinders honed out fine, and two had to be bored to .020 over. I replaced all four pistons, and carefully checked the ring gap before I put them in place.

good luck,
fp

 

[steelespike]

Re: Cylinder wall wear

Technically any groove is too much.Years ago I had a motor with grooves you could feel.I wasn't abouit to put more money into it at that time.I honed the cylinder
to break the glaze and put in a new piston and rings and it ran fine.Though under light duty.
You may want to have it bored for an oversize piston and rings.If you don't think it is worth it give it a good honing and new piston and rings.

 

[iwombat]

Re: Cylinder wall wear

After honing, there are times when you can visually spot a groove, but it's not big enough to feel or measure. I often employ the fingernail test. If I can catch a fingernail on it it's too big. Don't forget to clean it thoroughly after that and use assembly lube. The oils on your hand are very corrosive.

(Granted, any groove in a cylinder wall is undesireable, but sometimes we have to make choices over whether it's significant enough to go through a boring process.)

One or two moderate to small groves isn't the end of the world.

 

[iwombat]

Re: Cylinder wall wear

Be sure to check the bottom of the cylinder wall for cracks and other nasty damage where the broken rod may have done something very naughty.

 

[golden]

Re: Cylinder wall wear

How smooth do the walls need to be? I have to replace a busted connecting rod and piston. There are some small grooves. How do I know what's too much?

 

[golden]

Re: Cylinder wall wear

After honing, there are times when you can visually spot a groove, but it's not big enough to feel or measure. I often employ the fingernail test. If I can catch a fingernail on it it's too big. Don't forget to clean it thoroughly after that and use assembly lube. The oils on your hand are very corrosive.

(Granted, any groove in a cylinder wall is undesireable, but sometimes we have to make choices over whether it's significant enough to go through a boring process.)

One or two moderate to small groves isn't the end of the world.

 

[golden]

Re: Cylinder wall wear

THIS FORUM IS GREAT!
I was given this motor because they didn't want to spend the $$ to fix it. The piston had been taken out by a marine shop. I've ordered the manual and getting ready to take on this beast. I'm sure I'm gonna need lots more advice.

 

[emdsapmgr]

Re: Cylinder wall wear

An engine will run with small grooves after a rebuild. You will probably not even know the difference. The long-term problem is that exhaust gasses will migrate down the groove and will soot the rings and cause them to stick. This causes coking and other problems. An overbore is the best way to correct your problem.