Piston damage

[The Force power]

I have two spare ('89)Force 85 HP motors and both have one cylinder damage/low compression (70 psi)
The cylinder-wall are okay & I can Hone them.

please let me know if this piston damage is referred to as; melted piston

 

[Scott Danforth]

those pistons look like the rings broke and caught the port.

either way.... the pistons are junk.

you will need to mic the bores to determine if you can get away with just a hone, most likely you will need to bore them.

 

[The Force power]

those pistons look like the rings broke and caught the port.

either way.... the pistons are junk.

you will need to mic the bores to determine if you can get away with just a hone, most likely you will need to bore them.

The reason I'm asking;
My plan is to make out of two power heads one working one.
the Cylinder-walls are not bad (can barely catch the grooves with my nails)

I have worked on many Compressors & diesel engines as far as Piston/connection-rods/cranks are concern

Just to confirm, these are not "melted" pistons?

 

[Scott Danforth]

if you can catch a groove, its 0.01" deep.

however you have to measure the bore to see what the dimension is, and if the cylinders are round.

 

[alldodge]

Doesn't appear to be melted to me but maybe jerryjerry05 can weight in
I'm thinking not enough lube on the cylinder walls caused ring to catch

 

[Jiggz]

I'll say go for it. The only cost is your time and effort since you are just moving one set of piston from one to the other. And if you already have a cylinder honing kit, probably the only cost will be the new set of piston rings. There's a stamped on the piston crown to indicate if it's still a standard size or an over sized one. "1" means it's still standard size.

Highly recommend to at least replace the piston rings and de-glazed the affected cylinder. Put it back together and test for compression. You will still need to do a break in to properly seat the new rings.

 

[Nordin]

From what I see that is not a melted piston, as ScottDanforth says a ring caught at port.

I would go for Jiggz suggest, new piston with rings and hone the cylinder bore.
Go for a "small" run in procedure, with no WOT for a longer time and some "richer" oil ratio. such as 25:1.

This is not so unusual for the later Force with semikeystone ring at top and to little land at the piston.
Older Chrysler with regular rings did not fail for this from my experience.

Maybe as AllDodge says, lack of lube.

 

[jerryjerry05]

IF??? you can "catch a nail" on ANY groove, it needs a bore job.
If it's not absolutely smooth?? you'll be redoing the job again.

Your best bet is dismantle and find a machine shop that works on outboard blocks.
Have them check the groove and see how much needs to be removed??

The piston in the pic is a standard piston.

.010 -020 is pretty much what you can look for.

Once you get past .040 then you get into rejetting the carbs etc.

 

[The Force power]

Thanks all of you that tuned in & is giving me the advice, this will be my "winter project"
I like to have running "spare" for; just in case I needed in the Summer months

 

[jerryjerry05]

I had a rebuilt 87/85hp block in my shed for YEARS!!
Luckily I never needed it.
Have fun with the project.
Get a camera and use it and keep a journal of the job and this winter post
it as you do the job.

One thing that gave me fits!! The 3cyl has 3 locating pins on the crank journals (??)
Aligning these and getting the rest to fit was at time a PITA!!

God luck and keep us posted. LOT'S of pics.
Disassembly and assembly.

 

[The Force power]

I had a rebuilt 87/85hp block in my shed for YEARS!!
Luckily I never needed it.
Have fun with the project.
Get a camera and use it and keep a journal of the job and this winter post
it as you do the job.

One thing that gave me fits!! The 3cyl has 3 locating pins on the crank journals (??)
Aligning these and getting the rest to fit was at time a PITA!!

God luck and keep us posted. LOT'S of pics.
Disassembly and assembly.

Hey thanks Jerry for the encouragement, I'm not starting as of yet but now I'm curious about "the 3 locating-pins on the crank-journals align" part.

I'v only once done a Piston swap on A '73 Merc. 3 Cylinder and I'm not sure what you meant by the above?

 

[jerryjerry05]

You can see the pin and hole on the bearing.
The pin fits in a corresponding hole on the block.
The pin's already pressed in and the bearing needs to be turned until
the holes line up.
If its not aligned the crank turns slowly or not at all.

Find the parts diagram.
Open the piston/crank.
Look for the bearing and pin.

Unfortunately this site doesn't have actual parts diagrams, so look at boatsdonets
Force parts diagrams.

 

[The Force power]

Thanks Jerry,
when the day comes, I'll see & luckily I have the tear down Manual

 

[The Force power]

Another Piston question;

I could not contain my urge to start disassembling a block for the piston-swap.

So far these ones look better then the once posted earlier, however.....with these I noticed a difference between the three;
#1 has a B stamped in the center / #2 has a D stamped at the edge / #3 has "something" stamped at the edge of the piston.

I suspecting this motor has been taken apart before/pistons swapped

please spare me some of of your time and see the attached pics. and let me know your thoughts

 

[Jiggz]

I can only surmised that the standard Force/Chrysler pistons have been replaced with after market ones. And the only way to find out what over sized piston/standard is each is to do the micrometer reading. It could also be that the standard crown stamped of 1-2-3-4 could be directly correlate to A-B-C-D, just a suggestion.

Std - 3.312
.020 - 3.332
.030 - 3.342
.040 - 3.352

 

[The Force power]

I can only surmised that the standard Force/Chrysler pistons have been replaced with after market ones. And the only way to find out what over sized piston/standard is each is to do the micrometer reading. It could also be that the standard crown stamped of 1-2-3-4 could be directly correlate to A-B-C-D, just a suggestion.

Std - 3.312
.020 - 3.332
.030 - 3.342
.040 - 3.352

thank you Jiggz,

It sounds logical enough, in that case these Pistons may not be a candidate. In the other block all three pistons are stamped with a 1
I may have to re-think my plans

 

[jerryjerry05]

Usually an oversized piston is stamped with the oversize.
The standard pistons I have seen do have letters stamped on them, no idea what they mean?

Take them apart and see how the wrist pin is attached.
If it has a circlip holding it in? then it's aftermarket.
Pull a piston from the "bad" motor and compare it to the "good"

OR?? measure them??
Take to a machine shop.

 

[The Force power]

You can see the pin and hole on the bearing.
The pin fits in a corresponding hole on the block.
The pin's already pressed in and the bearing needs to be turned until
the holes line up.
If its not aligned the crank turns slowly or not at all.

Hi Jerryjerry,

I see what you meant (it's a similar to Merc. set up that have the valve-plates attached)
however these locating-pins are in the block

I noticed some scars/grooves in the block (intake side) this must be old and the reason the block has been opened before.
how else could that be there without any damage to the crank-bearings?

in the pic. (with the tip of the screwdriver pointing) initially I thought his this was a thrust-washer but upon closer inspection i saw it could not be one as it's actually on the crank & not in between.

after reading the tear down manual a little closer; I discovered there called crank-seals and need to be replaced.

I thinking these keep the pressures in the cylinder from escaping to the adjacent cylinders, finally my question;

If they are not cracked do they really need to be replaced?

 

[racerone]

Yes they are seals.-----Your motor has 3 separate crankcases..----Inspect them before deciding on replacement.

 

[The Force power]

Yes they are seals.-----Your motor has 3 separate crankcases..----Inspect them before deciding on replacement.

yes, I should of been a little more precised saying; keeping the pressures inside each crankcase.

I just found a guy that's selling two(1990) 90 hp force motors (with low compression & lower-units gone) for $250 Canadian
that's like $190 US.
I'm thinking to buy them so I have a few more options to put a Spare motor together