piston hitting?

I pulled the head on my 90hp 1985 rudet to find<br />the is little scuff marks and little nicks in a good part of the starboard side lower piston these marks or nicks are in direct proportion to the roughed up area on the top of the piston! The mechanic told me a pice of ring must of broke off but there is no scoring of the cylinder at least in the area above the piston that you can see when the piston is moved from top to bottom by moving the flywheel .It almost looks like the piston was hitting the top of the head, but how is that possible? but like i said the the rough spots on the piston and head line up! Also I just did a compression check last yr and i had between130 and 115 all the way around now after this they do a test again and they are all around 100 with the affected cylinder being 75! my question is how in the hell did the other 3 unaffected cylinders drop? the hole thing is screwy does anybody have any ideas on this/<br /><br /><br />thnx<br />mark

Re: piston hitting?

Mark, compression can change with ambient temp, amount of residual oil on cylinder wall...several things may affect a comp test.<br />You may have a piece of ring that caught on a port on the way up or down, and was pulled on top of the piston on the next stroke, being pushed to the top.<br />Are there any dings or nicks in the head??

Re: piston hitting?

ya kenny there are nicks in the head that are in direct line with the rough scuffed areas on the top of the piston<br /><br /><br />mark

Re: piston hitting?

Well, my suggestion would be to pull it down and find out what the problem area is, or what exactly has broken and got on top of the piston.

Re: piston hitting?

could the piston of hit the top of the head?<br /><br /><br />mark

Re: piston hitting?

Mark, Kenny has you on the right path. I dont think the piston has hit the head. Small pieces of broken ring got between the piston and the head. Go ahead and pull her apart.<br /><br />Starboard side broken rings (from coking) are not uncommon on those motors. I'll bet its propped in the low 5000 range. I'd also bet its been a while since the deflectors were changed. How often do you decarb?

Re: piston hitting?

DH and kenny thnx for replying, if a small piece of ring had gotten up there wouldn't it have scored the cylinder wall?.It looks smooth to my eye and feel. I wish I was good enough to pull her apart but that is way over my head. Is a total rebuild my only option? Can I not replace the head and bore and replace that cylinder? there is no way i can afford a $2500.00 rebuild. DH what do you mean propped? 5200rpm was about the top end at least with my prop.I am just hoping and grabbing for straws that i can stay awat from a total rebuild.<br /><br /><br />thnx<br />mark

Re: piston hitting?

Very typical to see a motor propped that low coke up the rings rather quickly. Eventually as the ring sticks in the groove more and more the piston loses support and will finally rock enough to shear off one end of the ring. <br /><br />You can continue to run it as is but its only gonna get worse (IE - more $$). The thing to do is get it apart and measure it up to see what it needs.

Re: piston hitting?

dh how can it get any worse than a total rebuild? at least that is what the mechanic said that pulled the head and ran the comp test. Does it sound like i have any option other than a total rebuild? and if so at what cost.<br /><br /><br />thnx<br />mark

Re: piston hitting?

pro What made you think there was a problem to start with? It could have been as simple as a piece of carbon breaking loose and getting smashed in that particular spot.<br /><br />Paul

Re: piston hitting?

If its run long enough it could start to have an effect on the rod bearing. We dont want that. Cranks are expensive. <br /><br />Right now I'd bet the crank and rods are good and the block is boreable. You'll need another head but I'd take the opportunity to find a set of late model heads and run those. Used heads shouldnt be a big deal.