low compression on 85hp force

[boatermarquis]

I believe its a late 80's like 88model on maxum 16ft boat.Middle cylinder reads 60,and read 90 with oil in cylinder then leaked straight down to 85-80.Top and bottom reading 130.I can;t get the numbers off it or anything right now,but wondering you guys thoughts on if it could be rings,cylinder walls,can a liner be put in cylinder if scratched bad.It don't sound like no rubbing.Just wondering worst case senario,and best.My dad has a boring kit for like kohler motor he did once.didn't know if maybe just hone job if ring bad,any thought please.This guy wants boat gone,and pretty cheap trade.

 

[boatermarquis]

 

[boatermarquis]

another thing i noticed like head part just had work done,had gasket sealer gray color,but didn't see a gasket,maybe i didn't know what i was looking at

 

[Frank Acampora]

First remove the head and see what the cylinder liner looks like. At 90 PSI, it could be lightly scored and a simple honing would do the trick. The piston MAY have a broken ring. Post a couple of good close up photos of the cylinder walls.

Inspect the head gasket and replace if anything looks damaged. The head is two pieces consisting of the head itself and a water jacket cover (finned. The jacket cover can be sealed with silicone but the head to block must have a gasket. To remove the head back out the (14) 1/2 head bolts. Do not remove the three 7/16 bolts next to the spark plugs. Do not remove the four slotted bolts retaining the thermostat cover unless you want to replace the thermostat.

It is not worth the money to replace the cylinder liner and you do need special tools. However, at 60-90 PSI, the cylinder definitely will not need replacement.

Once you remove the head you can also remove the piston by removing the carbs and manifold. Using a 1/4 inch drive 12 point, 1/4 inch socket with a 6 inch extension and remove the rod cap bolts. Then push the piston and rod out the head end. Since it is a job to reassemble the piston to the crankshaft, do this only if you suspect a broken ring.

 

[boatermarquis]

Ok so 60-90 means probaly not bad cylinder walls,i was going to get boat for around 350 trade,for some reason looks like they used silocone on head gasket on block,so maybe thats the problem

 

[robert graham]

You could inspect the inside of the cylinders with a bore scope....save you from having to remove the head. I expect the motor will run as it is and if the low compression readings are caused by piston rings stuck in their grooves by carbon then you might try to do a de-carb procedure with a product like Yamaha Ringfree.....The bore scope would be the first thing to try, just for an idea of what you have there....But Frank is a real expert on these motors!

 

[jerryjerry05]

At 60# you'll need to do some repairs.
Bought a 125 with 145# comp on all 4, removed the head to check(gonna sell)
Found scoring bad enough it needed a bore job.
Like the others suggested remove the head and post pics.
Being it has 3 carbs they will need to be gone through too.
I'll have a whole bunch of 85parts soon.

 

[Frank Acampora]

From the photo, the boat and engine appear to be in decent shape for their age. That said, $350 is not a lot to pay for the package (as long as the interior is not completely trashed) even considering the engine may need some repairs. These engines are dirt simple to work on so almost any repair can be done by yourself. At $350 that's a gamble I would take---spent 300 for a 150 engine with two bad cylinders.