Replace Piston Force 1251X9D

[gregmsr]

Well, time to crap or get off the pot, bite the bullet, take the dive and get started on "trying" to replace the bottom piston as was described in my ancient thread "Force 1251X9D Bottom Cylinder Issues". For those interested (the old post has been dormant for over 90 days) if I could find some info here on swapping out that piston without removing the entire head. I have rebuilt car engines so I think I can do this with some help here and my Clymer Manual.
I will keep searching posts but if anyone can chime in with some general step by step instructions I would greatly appreciate that.

Thank you

I'll try and post a link to my old thread.

 

[Frank Acampora]

Re: Replace Piston Force 1251X9D

Greg: There are quite a few old posts on this.

Simply put, if the cylinder is not scored you can remove the head and remove the bottom carb and manifold. Then through the reed opening remove 1/4 inch 12 point bolts and the bottom of the rod. Push out the piston through the top of the block. Count and account for all 16 rollers. Replace with a good piston and compress the rings so it can be pushed all the way in. Insert rollers and cages with grease to hold them and finess the rod cap back on. Remember it is different than autos and only goes on one way. Then check to be sure the cap is aligned correctly. Tighten the 12 point bolts to 180 inch pounds or whatever your manual calls for.

 

[jerryjerry05]

Re: Replace Piston Force 1251X9D

You know if your gonna do only one cylinder, what are you leaving in the other 3.
It's 20+ and should be taken all the way down.New rings at least.
I've never been a fan of just doing one cylinder. It's done, but I don't like doing it.
How bad is the scoring??

 

[gregmsr]

Re: Replace Piston Force 1251X9D

The scoring don't look or feel very bad, I don't think. I have good compression in the other three (132 +-, the one with the problem is around 120+-psi)). I really haven't given much thought to going further into it. Maybe that's the right thing to do while i'm at it. (My wife got her hardwood floors now it's my turn .
Can I get a good bore measurement with the pistons still installed? If this is good, maybe just a hone to de-glaze and new rings.
I like the idea of total overhaul but right now not sure. Let me dig into it. Thanks.

 

[gregmsr]

Re: Replace Piston Force 1251X9D

Can I get a good bore measurement with the pistons in?
The reason I ask this is I have read to measure in three levels, top, mid, and below exhaust port?
If the pistons are still in, I cannot measure below them.
Do I even need to measure below them?

 

[Frank Acampora]

Re: Replace Piston Force 1251X9D

At 120 PSI, you don't have a major damage condition. I would not bother to measure the bore or even replace the piston unless the piston itself shows damage. You may have a stuck ring or POSSIBLY a broken ring. But at 120 PSI, I doubt a ring is broken. Broken rings USUALLY bring compression down to around 60 PSI.

Try a decarb first unless your problem prevents you from starting the engine.(I don't remember your last thread--I don't remember what I had for breakfast)

Since the piston and rings travel below the exhaust ports, you must measure below the ports for accuracy. Tolerance is tight: MAX .002 for wear, taper, or barrel shape. However, OMC uses .005 so If it were my engine I might just make a judgement call if I were close.

 

[gregmsr]

Re: Replace Piston Force 1251X9D



Trying to attach pictures of the top of the piston showing damage.

 

[gregmsr]

Re: Replace Piston Force 1251X9D

It worked. As you can see the damage.
The old thread shows at the bottom of the page (Bottom Cylinder Issues).

 

[Frank Acampora]

Re: Replace Piston Force 1251X9D



Ahh, yes! Broken ring for sure! I am surprised that you are still getting 120 PSI but that shows that there is not much damage to the cylinder. Remove the piston and rod by taking off the rod cap through the reed opening and push out the piston. Simply do a light hone on the cylinder (assuming no deep scoring) and insert a new/used standard sized piston (again, assuming the block has never been bored.

Tools: 3/8 drive inch-pound torque wrench, adapter from 3/8 to 1/4 inch drive, six inch long 1/4 inch drive extension, 12 point 1/4 inch drive -1/4 inch size socket.

Re-torque rod cap bolts to 180 inch pounds. Look up other posts that detail how to replace bearings and check for correct alignment.

 

[gregmsr]

Re: Replace Piston Force 1251X9D

I think the pistons have the number 1 stamped on the top but I don't think it's been bored out. All right, off to find parts. I'm the slowest mechanic around but i'll post results soon as I get going. Thanks to all.

 

[gregmsr]

Re: Replace Piston Force 1251X9D

A couple things;
1. Is it better to remove the mid section for better access to the bottom cylinder (for honing, and I want to remove the exhaust plate also and install new gaskets because i think that's how the water is getting in the bottom cylinder)?
2. I don't mean to be lazy finding all the parts I need to replace this piston Frank's way, but just looking on-line there are several sites to order from. It's mind boggling to me wading thru all the diagrams and searching for just the couple gaskets i will need.
Is there any way I can get a parts list from someone with part numbers from the simplest web site? Maybe someone has them memorized! Never hurts to ask!
Thanks.

 

[Jiggz]

Re: Replace Piston Force 1251X9D

Exactly the same problem I had with my #3 piston, the ring caught on one of the ports. Replacing it is very doable and even better replace it with those Wiseco Pistons kits that comes with their own wrist bearings and rings. However, you might want to disassemble first de-glazed and then measure before ordering the piston kit. You will also need those gaskets for the intake manifold and adapters. Re-installing the rollers to the journal was my hardest portion of the job. I used triple duty grease which is really thick to hold them in place to install. This was my first too so I made sure I can put it back together accordingly by taking a lot of pics before and after. I mean its digital cam anyways.

 

[gregmsr]

Re: Replace Piston Force 1251X9D

I suddenly got busy at work but i am trying to find parts and save time when I get started. You know how many times a person orders the wrong parts or orders the right parts and gets the wrong ones, etc.
Also do as much research as possible before tearing into it! Any and all help is appreciated! Thanks.

 

[Frank Acampora]

Re: Replace Piston Force 1251X9D



Just to avoid confusion in the PM: here are a couple of photos of the reed plate and manifold assembly. First photo is reed plate only last photo shows an assembly remove as a unit. If possible remove the manifold with the reed plate attached to save one gasket. These gaskets need not be ordered--they can be made with regular gasket paper, a good sharp xacto knife and scissors, and a child's hole punch.

Typically the original gaskets will be self-glued to the block. You will need to use a long screwdriver or punch and hammer at one corner to break free the reed plate.

 

[gregmsr]

Re: Replace Piston Force 1251X9D

Classic water intrusion. Can you guess which cylinder?

Question; What does the number 1 stamped on top my pistons mean?

 

[jerryjerry05]

Re: Replace Piston Force 1251X9D

That 1 is probably just a manufacturers casting mark.
If it was bored out and resized it would have someting like this. .010 or .01 something like that.
From the water and the rings.you need to do a complete rebuild.
FG1026-1 This is the part# for the factory gasket set.About $125
There are cheaper set out there.
E-bay is a good bet for a cheaper set.

 

[gregmsr]

Re: Replace Piston Force 1251X9D

You think?
A complete rebuild due to water? (did water damage bearings or something else?) Where is the water coming from? I replaced head gasket, still have water. I just removed the exhaust plate but did not see obvious leakage although I am not finished cleaning it up. So, where is the water coming from? Remember, I have a crack in the block outer water jacket. Is the block cracked somewhere else, like on the intake side? Who knows.

 

[pnwboat]

Re: Replace Piston Force 1251X9D

Seen many engines with water intrusion in the lower cylinder cause by a bad exhaust cover gasket. Not saying that's necessarily the case in your situation, but it's a good possibility.

I did have one motor, a 1988 125HP that had water intrusion issues. Replaced the exhaust cover gaskets, head gasket, no good. Had the block decked and head trued up, still no good. Had to replace the block to fix the problem. Never did find out where the leak was.

I did have to replace the crank and rod on the cylinder that was getting water. The rod itself was pitted on the big end where the needle bearings ride, and the crank journal and needle bearings were all blue from excessive heat. Machine shop said it was not unusual to see this type of damage from water intrusion. Water on the bearings caused the needle bearings to "stick" rather than roll or something like that.

 

[gregmsr]

Re: Replace Piston Force 1251X9D

Ugh, don't sound too good.
I believe what I'll do is go ahead and install new exhaust plate gaskets and see if that cures the water problem. Then seek more advice!
Thanks.

 

[pnwboat]

Re: Replace Piston Force 1251X9D

I would agree with your approach. Take a close look at the rod journal on the crank, and rod bearings. If nothing is "blued" from excessive heat, and the bearing surface on the rod itself is smooth and not pitted, go ahead with replacing the exhaust plate gasket and see how that works.