bore one or both?

[oldcatamount]

I have a 1990 4hp Johnson with a scored cylinder wall. Bottom cylinder has 138lbs. and the top cylinder has 90lbs. I took the head off and I can feel the scoring (cracked ring from carbon build up I think). Can I have just that cylinder re-bored and leave the other one alone or do I need to re-bore both?

 

[Bifflefan]

Re: bore one or both?

I have never done just one in any kind of motor. I have and do hand fit each piston to each hole, but thats a different story.

That being said,
I took a car engine apart once that had one of cylinders bored over size by 010. In a different engine I found one of the rod journels had been turned 010 and the rest at standard.
Both of these had been done at the factory, I found this odd. The man that tought me to build engines had seen this many times in his decades of building and said that was normal practice for the times, when there was no reason to fix what was not broken.

So, yes it can be done, but you may as well do both.

 

[F_R]

Re: bore one or both?

I've rebuilt many, many motors, boring just one or more cylinders. Can't tell the difference. Boring a perfectly good cylinder is a waste of time and money, not to mention the waste of good metal that can never be replaced in the future, should another rebuild be required for some reason.

 

[kenmyfam]

Re: bore one or both?

I'm with F_R. If there is nothing wrong with the other one then leave it alone. If it is suspect then do that one as well.

 

[oldcatamount]

Re: bore one or both?

Thank you for the expert advice! I will bore the one bad cylinder and leave the other alone.