piston to cyl head clearance... 3 cyl looper

[ct1762@gmail.com]

My machine shop called me to say they had to deck the block on my 1985 70hp . It's the 49ci . they had to take of 10 thousands to get a bad chip out of it when the head was taken off becuase of a frozen bolt. I'm worried that my brand new vertex pistons will slam into the head with that much taken off. Does anyone know if this will be an issue? Compression will be raised, so ill run it a few sizes rich on the mains. he mentioned shaving the tops of the pistons for proper clearance, but i take all my blocks to the machine shop for precisely this reason... don't have micrometers or a bore gauge and the shop is an hour away!

 

[ShoestringMariner]

My machine shop called me to say they had to deck the block on my 1985 70hp . It's the 49ci . they had to take of 10 thousands to get a bad chip out of it when the head was taken off becuase of a frozen bolt. I'm worried that my brand new vertex pistons will slam into the head with that much taken off. Does anyone know if this will be an issue? Compression will be raised, so ill run it a few sizes rich on the mains. he mentioned shaving the tops of the pistons for proper clearance, but i take all my blocks to the machine shop for precisely this reason... don't have micrometers or a bore gauge and the shop is an hour away!

Is there such a thing as a thicker gasket?

Surely .010” isn’t going to put it in the “strike zone”, is it? Do old, worn out motors full of slop ever start pounding into the head when the crank, rods an pins are tired and sloppy and screaming at 5500 rpm?

Can you check actual clearance with a straight edge and feeler gauges?

Use plasti-gauge?

 

[ct1762@gmail.com]

Hey that's a good point about older, tired motors! Yea i was just going to check how much, if at all, the piston protrudes over the cylinder. now i just hope it didn't increase compression too much. Don't want a motor that will only run on premium without detonating. honestly i'm not even sure if the piston is capable of hitting the head with 10 grand , but better to ask than to be sorry. i guess i could have them shave 10 thousands off the tops of the pistons, just don't know if that will weaken the top rings?

 

[ShoestringMariner]

I’m just trying to save you some money. What about checking on some racing forums?

 

[ct1762@gmail.com]

i appreciate it. i asked an old OMC tech about this and he laughed at me for worrying just like you said haha. he said if you are really paranoid, take some modelling clay or nephew's play-doh and put a ball on top of the piston to see if its hitting the head, but he said forget it you are fine.

 

[Faztbullet]

Put gasket on it and go. Might have raised compression 2-4 psi. If under .020 oversize go up maybe .001 on main