1985 yes another 170 mercruiser engine question

[mjwellcraft]

Hers the short version I took my head off after checking compression 150 psi or close in first 3 and in # 4 had 35psi. Found a
hole in the piston on the inside wall along the edge facing from the front. ok my question is what might cause this and what can I do if there is some small dimples in the wall? Looking to do this very reasonable. Been told a lot of things about this motor and read a lot on here to but need to here from the experts on this motor its a 3.7L 170hp mercruiser? Thanks

 

[alldodge]

Re: 1985 yes another 170 mercruiser engine question

:welcome: to iboats

Holes in pistons and burned spots are caused by preignition and detonation. The timing or the engine was off enough to cause increased stress. If fuel is ignited while piston is still coming up will damage the engine.

 

[stonyloam]

Re: 1985 yes another 170 mercruiser engine question

That hole and pitting was probably caused by coolant leaking into the #4 cylinder. Was the inside of the head also pitted? Take a look at the #4 sparkplug, bet the insulator will be white. As for the cylinder wall, ya gotta pull engine now anyway, so best take it to a machine shop for an opinion.

 

[Eric 3.7LX Alpha 1]

Re: 1985 yes another 170 mercruiser engine question

If it's needed the bore can be oversized to clean it up, (which will done to all 4)

If boring doesn't work, a sleeve can be pressed in to cover the cylinder and the sleeve can be bored to the correct size.

 

[blkzoe]

Re: 1985 yes another 170 mercruiser engine question

If it's needed the bore can be oversized to clean it up, (which will done to all 4)

If boring doesn't work, a sleeve can be pressed in to cover the cylinder and the sleeve can be bored to the correct size.

470's can be sleeved? If so, source of the sleeves? I don't have a need at the moment. Just another piece of useful info. Thanks!

 

[Eric 3.7LX Alpha 1]

Re: 1985 yes another 170 mercruiser engine question

470's can be sleeved? If so, source of the sleeves? I don't have a need at the moment. Just another piece of useful info. Thanks!

I don't know the source of the sleeve, but if you read this thread from the past, you will see it has been done on one before:
http://forums.iboats.com/mercruiser-i-o-inboard-engines-outdrives/mercruiser-3-7-rebuild-296513.html

his engine machine shop got the sleeve for it.

 

[mjwellcraft]

Re: 1985 yes another 170 mercruiser engine question

Thanks alldodge for the welcome I guess u could say u hit the nail on the head. The timeing must of been off. Well got 5 years out of it before it gave way... Thanks all for the response I took it in and there going to bore it and put new pistons rings ext in it.... Hope to get a another 5 out of it will see ha.... Thanks

 

[Eric 3.7LX Alpha 1]

Re: 1985 yes another 170 mercruiser engine question

Here is the tune up chart and a TSB regarding timing for your engine

 

[stonyloam]

Re: 1985 yes another 170 mercruiser engine question

If the inside of the combustion chamber was also pitted it was not timing. It was coolant intrusion into #4 cylinder, a particular quirk of the 470.

 

[mjwellcraft]

Re: 1985 yes another 170 mercruiser engine question

If the inside of the combustion chamber was also pitted it was not timing. It was coolant intrusion into #4 cylinder, a particular quirk of the 470.

Ok thanks stonyloam Iwill have that investigated to... I hope with all new parts and gaskets it should be right. The guy
that's doing the work as don quite a few of these and wants to go to a different piston and shave the head down also..

 

[stonyloam]

Re: 1985 yes another 170 mercruiser engine question

Yeah the top of my #4 piston and the combustion chamber was pitted, but was still usable.

 

[mjwellcraft]

Re: 1985 yes another 170 mercruiser engine question

I didn't see mine look all that bad on the top clean but not pitted.... I did a leak down to and nothing showed up. But I hear these engines
r very sensitive but if u build them right there bullet prove at least I have heard that some where ha....

 

[dmatthews5000]

...

 

[dmatthews5000]

Posting duplicates sorry...

 

[dmatthews5000]

Saw this old forum and I am new here and couldn't find how to post a new topic so I will piggy back, but any advise to getting mine to turn over. Had it out Friday night and ran pretty good. Filled it with fuel Saturday and put it in the water and wouldn't start. After a while finally started but died 30 seconds later just as I was pulling out of the docking area and wouldn't start back up. Had to get towed back in. Any ideas on where to start and look at? I am not that mechanical so simple is better. Been messing with the carb a little but hasn't helped. Choke plate is real loose but that may be as much as I can tell you at this point until I start messing more with it. Thanks!

 

[GA_Boater]

Saw this old forum and I am new here and couldn't find how to post a new topic so I will piggy back, but any advise to getting mine to turn over. Had it out Friday night and ran pretty good. Filled it with fuel Saturday and put it in the water and wouldn't start. After a while finally started but died 30 seconds later just as I was pulling out of the docking area and wouldn't start back up. Had to get towed back in. Any ideas on where to start and look at? I am not that mechanical so simple is better. Been messing with the carb a little but hasn't helped. Choke plate is real loose but that may be as much as I can tell you at this point until I start messing more with it. Thanks!

Please do not post in topics older than 90 days, thanks. Start a new topic by clicking on "Create + New Topic" at the top of any forum. :closed_2: