Rebore cylinder? Or not?

westjr8

Seaman Apprentice
Joined
Mar 13, 2011
Messages
35
1984 70hp Mercury
SN 6230127

Question. I burned out a piston and am in the process of replacing it. Earlier today I pulled out the crankshaft to expose the bad piston and cylinder. The Piston and rings were shot, but I think the cylinder will make it. There is no "scratch" in the cylinder wall, however, there is a slight, smooth groove on the wall. It doesnt catch my finger nail but i can feel the imperfection. About 90% of this groove on the wall behind where the piston would rub against it. Does this call for a re-bore and an over-sized piston? I can post pics if it helps!
 

ONERCBOATER

Chief Petty Officer
Joined
Oct 11, 2010
Messages
536
Re: Rebore cylinder? Or not?

post a few pics please.... preferably from dif angles and lighting ...

Sean
 

westjr8

Seaman Apprentice
Joined
Mar 13, 2011
Messages
35
Re: Rebore cylinder? Or not?

IMG_0070.jpg

IMG_0069.jpg

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Here are 4 pics of the bad cylinder. Notice the melted aluminum at the bottom (the head) of the cylinder.

I talked to the machine shop today and they said the cylinders have already been rebored previously. They would not just resleeve the one bad cylinder, they would do all three. Is it possible to resleeve just my bad cylinder and not the others?

Can I drop a new piston/rings in the bad cylinder as is and get a few more years out of it? Or am i doomed for failure in the very near future if I decide not to fix the bad cylinder?
 

James R

Commander
Joined
Feb 1, 2007
Messages
2,678
Re: Rebore cylinder? Or not?

From the pics that cylinder is done. Wasting money trying new rings and piston, Measuring the bore will show. If the bore has enough meat it can be rebored and new piston and rings fitted.
It depends on how much you are prepared to spend but I expect it can be resleeved. Frankly if it has been bored before I would be looking for another power head.
 

westjr8

Seaman Apprentice
Joined
Mar 13, 2011
Messages
35
Re: Rebore cylinder? Or not?

How much does it cost to resleeve a cylinder? And, can you resleeve just one cylinder, or is the machine shop going to want to do all 3 cylinders?
 

James R

Commander
Joined
Feb 1, 2007
Messages
2,678
Re: Rebore cylinder? Or not?

You can resleeve one cylinder. Cost varies but $150 to $250 is common.
 

sschefer

Rear Admiral
Joined
Nov 13, 2008
Messages
4,530
Re: Rebore cylinder? Or not?

That cylinder looks like it will clean up with a .030 bore. I've seen worse but you first need to run a bore gauge through it and see how deep the scoring is. Strip it down to the bare block and then find someone who can bore a blind hole and get some advice. If it needs a sleeve 150-200 will get you a new sleeve but revoving the old one and installing and porting the new one is a shop job and must be done by a truly qualified shop. You may be able to find a used sleeve out of another engine and that will cut the cost significantly. A good source for new sleeves it LA Sleeve.
 
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