Low Compression on Cylinder #2

FWDan

Seaman Apprentice
Joined
Apr 22, 2016
Messages
32
That sound like a good deal! Is it oversize pistons?
Maybe find a machine shop and have them look at it to determine what oversize you should be ordering.
Maybe have them chamfer the ports at the same time, I know I would do it when in there!
And like Jerry said, try and figure out why it clipped the rings. Chances are when you reassemble it you also fix any leaking gasket it had beforehand.
It could also be due to carbon build up and you just got unlucky.
I'm not sure all will require oversize pistons, until they are measured and cleaned up. Trying to find a machine shop in my area that can do it. Not having much luck so far. Regarding cause, what about water in fuel? I had that problem early this summer. Engine stopped while motoring across the lake. Ended up being water in the tank.
 

las

Petty Officer 2nd Class
Joined
Sep 22, 2014
Messages
154
I'm not sure all will require oversize pistons, until they are measured and cleaned up. Trying to find a machine shop in my area that can do it. Not having much luck so far. Regarding cause, what about water in fuel? I had that problem early this summer. Engine stopped while motoring across the lake. Ended up being water in the tank.
In my experience water doesn't do any damage to cylinder or piston when running. But carbon build up could seize the ring, making it catch the port opening. A piece of carbon could fall of and lodge itself under the ring or the port.
It could even be something else being sucked in.
Could even be that the water helped loosen the carbon! Lot's of possibilities for failures.
Many times these catastrophic ring failures could be avoided with a chamfering of the ports, in my experience and especially if the ports are wide without much ring support.

Edit: with a bore you will need oversize piston!
 

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
17,096
Can't find anyone to do the bore job?
Call the local marine sales/service and ask the service manager who they use??
 

FWDan

Seaman Apprentice
Joined
Apr 22, 2016
Messages
32
I called around last week looking for a place to do the machine work and only found one, so far. They want $75 a hole to bore, $30 to machine hone and $10 to hand hone. Thanks Jerry, I'll be calling sales/service places this week to see who they use.

Until measured, I don't know if 1, 2 or all 3 holes will require oversized bore and oversized pistons. I didn't have time to pull the powerhead this weekend. Once I do though, I plan to take the block to a machine shop along with the bore size limits to see what they say. My Seloc book says for my 1995, 70hp Force motor the standard bore is 3.3750 with a service limit of 3.3762, max taper 0.002 and max cylinder distortion 0.0005. Since I don't have a real service manual, does anyone know if the full up service manual numbers agree? Does anything outside these numbers require an oversize bore?
 

las

Petty Officer 2nd Class
Joined
Sep 22, 2014
Messages
154
When you get it bored it will require oversize pistons! and worn cylinders out of spec will require a bore.
I would recommend you get all barrels measured and then take it from there.
If they are out of spec, have them bored at the same time.
But do change the rings on all cylinders and get a hone on the ones you don't bore if that's the route you go.
But ask the shop what they recommend, always a good idea. They should be the experts after all.
And like I mentioned earlier I would chamfer the ports for better longevity, but others might disagree. It's your choice.
 

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
17,096
Have the shop tell you if it needs a bore or a hone.
The middle piston(if I read right) was the bad hole and needs the bore job.
You don't need to do all 3 holes unless they're damaged.
There are lots of 3 and 4 cyl Forces running around with 1 over sized piston.
On the Eastern Shore of Va. is a 125 I rebuilt 2010 only needed 1 piston.
That said any more than .020 over and then I look into boring the others.
Any more than .020 and you need to look into re-jetting the carbs high speed jets.
I said figure out why it went bad(said nothing about clipping a ring) if the motor EVER backfired or even coughed it could blow a gasket in a couple different places?? The port cover being the first place I'd look. Especially the cover with the fuel pump.
The gaskets are thin and put in with no sealer and blow out easily and sets the motor up for sucking air and running hot on that cyl. causing the rings to fail.
 
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