1989 Force 125 blown cylinder

[FlightsRin]

Well, after much research on here and asking questions, I got this motor revived and running great for two weeks. Last week Thursday, I had my wife and kids out for a little joy ride and we were idling along at about 3-4 mph when the motor locked up and stopped immediately. Motor wouldn't restart without choke, finally started and limped to the launch. Re-timed, re-synced, etc, and nothing would get it going again. Finally grabbed the compression tester and all cylinders tested 135-141, however cylinder 4 was at 75 lbs. Pulled head and found this........ Looks like ring grenaded and killed my cylinder/piston. Now what do I do? Not sure where i go with it. Only ran this motor for two weeks and loved it, was running great because of all the help I recieved. Do I repower and move on? Thanks for help.

 

[FlightsRin]

more pics........

 

[flyingscott]

Were you running a 25-1 mix in it? Were you doing the break in procedure?

 

[Jiggz]

I had the same issue back in 2011. Yup, what happened is the rings got caught with the exhaust ports. From the pic, it doesn't look like the gouges are too deep (doesn't catch with a finger nail) that you cannot try fixing it. Your next move should be:
- Remove the head and try to save the head gasket if possible (order a replacement head gasket)
- Remove the bottom carb, inlet adapter and Reed V block (make sure you order gaskets)
- You will need 12 point 1/4 socket and extension to remove the piston rod caps, watch out for the roller bearings. To ensure you do not lose any, stuff the lower part of the motor head with rags to catch any roller bearings falling of the cavity.
- Push out the piston and rod out of the top end. Check what size is the piston (if it's oversized or standard). Usually, there is a stamped on the piston crown, "1" means it is still standard size.
- Order a replacement piston and rings according to size.
- De-glaze the cylinder and if possible file (chamfer) the edges of the intake and exhaust ports using a conical grindstone to avoid this from happening again.
Re-install new piston and rings. Post again for further steps.

 

[jerryjerry05]

The first pic shows a 1/2" gouge in the bore.
If you can feel the edge, it needs to be bored out.
Find a machine shop that works on outboard blocks(not all do) and show them and see
how deep the bore's gotta go??
Usually .020 is enough to clean it up.

It's not a hard job just a big job.


You need to figure out why it let loose??
Get hot? no oil? recirc system clogged?

 

[craigcharles]

Jiggz, when reinstalling the new piston, how do you keep the roller bearings and cage all together on the piston rod? Same with the rod cap side when working through the reed block.

Thanks

 

[racerone]

Entire block needs to come apart for this kind of work.-----I do not believe you can line up a rod cap properly by working through the reed block opening.----Grease is one way to keep needle bearings in place if you insist on a short cut.

 

[Jiggz]

Jiggz, when reinstalling the new piston, how do you keep the roller bearings and cage all together on the piston rod? Same with the rod cap side when working through the reed block.

Thanks

I used triple guard grease which is thick enough to hold both in place.

 

[jerryjerry05]

They recommend using assembly grease on the bearings.
The triple guard is actually too thick and won't wash away like the assy. grease.
Can actually burn the bearings, or so the book says.

 

[craigcharles]

Thanks! will give it a try. Pistons are ordered and on the way.

 

[racerone]

Rod caps nave to be carefully lined up.-----Not sure how you would do that working through reed block openings ??

 

[craigcharles]

I have read on another thread where it has been done through the reed block opening..... easy enough to disassemble through it.. guess I will see how hard it is to assemble!

 

[racerone]

These have roller / needle bearings.----You have to make sure there is NO STEP to catch the roller at the joints on the cap !

 

[Nordin]

I have done it at a couple of Chrysler 70/75Hp and the design at the Force is the same.
Disassemble is no problem just do as jiggz says, put rags in the bottom of the crank case/intake of the cylinder you suppose to change piston.
There are 16 rollers at the rod and they are loose in the cages.

The assemble can be a PITA but it is possible with patient and maybe a couple of tries.
I used a smal amount of grease to hold the rollers in place.

As racerone mention it is important to line up the caps with the rod and when you do it with a split power head as the service manual describe, you check the line up by drawing a pencil tip over the cap/rod crack and you should not feel it.

I performed this with one of my nails when I did the change at the Chryslers.

You can search at this form for more advise, Frank A has explained how to do it.