1988 yamaha 175 low compression

[dodgeram082500]

Hey all, new to the forum here and found it in my search for answers with my issue with my motor.

I believe what happened is the oiler went out one of the middle cylinders and stuck or broke a ring (will find out for sure later today when we pull a head to see how bad the damage is. My question is if the cylinder wall isn't hurt is it acceptable to change one piston (assuming all others are still ok) or do we need to change all in the powerhead?

Also I'm a decent mechanic ,but how hard is it to rebuild these compared with the inline motors.

Thanks for any help

[boscoe99]

There is no reason that just one piston cannot be changed and for the motor to run just fine. Even if an over sized piston is needed.

Be prepared for all kinds of answers. Some will say just fix the one hole. Some will say that all six must be opened up to the same diameter.

The street value of a 1988 175 Yamaha is not going to be much. I suspect that you might not want to be putting thousands of dollars into a repair. Maybe so though.

Why do you suspect the oil pump? If five cylinders got lubed why would one not get lubed? Until you remove the head and piston it will be tough to make any calls as to what needs to be done, and whether to do it or not.

[dodgeram082500]

There is no reason that just one piston cannot be changed and for the motor to run just fine. Even if an over sized piston is needed.

Be prepared for all kinds of answers. Some will say just fix the one hole. Some will say that all six must be opened up to the same diameter.

The street value of a 1988 175 Yamaha is not going to be much. I suspect that you might not want to be putting thousands of dollars into a repair. Maybe so though.

Why do you suspect the oil pump? If five cylinders got lubed why would one not get lubed? Until you remove the head and piston it will be tough to make any calls as to what needs to be done, and whether to do it or not.

Just a hunch running low compression on 1 cylinder is something I've seen on other 2 strokes (not outboard)
It has individual oil feed lines to each cylinder if one of these had an issue it would starve a single cylinder of lube likely causing scored piston and stuck or broken ring. Or at least that's my perception but I'm no outboard expert. This engine only has 250 hours on it.

Best case senerio I'm thinking hone and new piston ring and gasket set. I'll post a vid of it running soon

[ausnoelm]

Just make sure you fix the lean burn on that cylinder, or buy 2 lots of parts to be prepared for the second rebuild.

[dodgeram082500]

There is no reason that just one piston cannot be changed and for the motor to run just fine. Even if an over sized piston is needed.

Be prepared for all kinds of answers. Some will say just fix the one hole. Some will say that all six must be opened up to the same diameter.

The street value of a 1988 175 Yamaha is not going to be much. I suspect that you might not want to be putting thousands of dollars into a repair. Maybe so though.

Why do you suspect the oil pump? If five cylinders got lubed why would one not get lubed? Until you remove the head and piston it will be tough to make any calls as to what needs to be done, and whether to do it or not.

Yamaha 175: Yamaha 175 - YouTube

[boscoe99]

A bit premature to be discussing a lean cylinder isn't it? We don't even know what the damage consists of let alone what caused it.

[rodbolt17]

doesn't take much oil to almost none to lube a piston.
oil issues typically show up as rod bearing big end failures.

piston analyisis will tell the story, however most techs have no clue how to read the skirt,lands or cyl walls to figure out why it failed.

[dodgeram082500]

doesn't take much oil to almost none to lube a piston.
oil issues typically show up as rod bearing big end failures.

piston analyisis will tell the story, however most techs have no clue how to read the skirt,lands or cyl walls to figure out why it failed.

First pic..........

[dodgeram082500]

First pic..........

it does look like lack of lubrication caused the issues left bank center cylinder is the one that had an issue the other on the other side also has some very faint marks. all other cylinders look fine. I don't see it being a lean issue because theres no evidence of it on the top side of the pistons. my guess is when it comes the rest of the way apart my guess is it will have gaulding on the piston skirts and stuck or broken rings the cylinder looks as though they'll clean up with a couple thousandths hone either way looks like a set of pistons.
I think I'll mix my own fuel/oil ratio from now on regardless.

[ausnoelm]

You think that it looks like the two centre cylinders did not get oil?

[dodgeram082500]

You think that it looks like the two centre cylinders did not get oil?

That's my perception

[ausnoelm]

I think you might be just s tiny bit optimistic on your "couple of thou hone" those are pretty deep scores, looks like you might have tried some sand paper on the bore already?

[dodgeram082500]

I think you might be just s tiny bit optimistic on your "couple of thou hone" those are pretty deep scores, looks like you might have tried some sand paper on the bore already?

Most of what your seeing is gaulded aluminum on the walls. Yes I hit it very lightly with 320 fine grit a couple of strokes and they seem to come right out. On a different note is anyone familiar with the similarities between the 175, 150, and 200 yamaha of this year as far as powerhead is concerned

[boscoe99]

Remove the oil pump and spin it with a drill motor. You will be able to see if it is oiling all six cylinders or not. I am betting that it is.

You can use muriatic acid to remove aluminum from the cylinder walls.

Go to the parts catalog and look at the block part numbers for the various models. If the part number is the same then the same block is being used to get ********g HP's. Quite common.

[boscoe99]

Remove the oil pump and spin it with a drill motor. You will be able to see if it is oiling all six cylinders or not. I am betting that it is.

You can use muriatic acid to remove aluminum from the cylinder walls.

Go to the parts catalog and look at the block part numbers for the various models. If the part number is the same then the same block is being used to get various HP's. Quite common.