1989 Force 125hp outboard & its rookie owner :)

[theoldwizard1]

Re: 1989 Force 125hp outboard & its rookie owner

NO! Let the shop "Mike " the cylinders first before buying pistons. Let them tell you how much the cylinders need to be bored then buy the correct sized pistons. The pistons are made in .010, .020, .030, and .040 oversized and are made to tolerances to provide correct clearance in an overbored cylinder. The machine shop bores to the correct size plus or minus about .0002 for tolerance.

You are correct. It the machine shops call on boring and what size pistons to order.

My point was, what are the tolerances from the factory on pistons ? If you get a piston that is 0.0005 over and the bore is 0.0005 under you could have an interference or at a least rings that are too tight.

 

[Frank Acampora]

Re: 1989 Force 125hp outboard & its rookie owner

Pistons are cam ground, not perfectly circular, and tapered to account for uneven heating when running. As far as I know, NO piston manufacturer will supply its tolerance specifications. I don't think the engine manufacturers do either. Suffice to say that today, they (tolerances) are so tightly controlled that if the cylinder is correctly bored, the piston will fit correctly. Note that Wiseco does recommend a little extra ring gap or piston clearance (I forget which because it is not important to me) in engines which are modified (for racing) or have aftermarket reeds. However, I simply slam in the stock Wiseco pistons in the correct overbore in my ported engines and forget about any extra clearance. I have yet to have a problem because of insufficient clearance.

Also note that wear, out of round, and barrel shape tolerance for Force engines is .002 (extrapolated from Chrysler specs) and for OMC it used to be .005. A couple of 0001 difference from nominal on each part will not cause slop or interference.

 

[adamjoelmusic]

Re: 1989 Force 125hp outboard & its rookie owner

Frank, once again I really appreciate your time here & all the advice! Like I said before, I am fairly mechanically minded but never having wandered into this part of the engine world, the unknown is a bit overwhelming ... So I definitely appreciate the counsel

I plan to locate a machine shop today to get the ball rolling ... Essentially, what I hear you saying is to let them start the process with a micrometer, from there they'll determine how much boring needs to be done & give me the tolerances for the pistons?

Should I plan to completely remove the power head for this? Also... Do you have a goto place for ordering these parts?

Rookie questions, I know

But I appreciate you all bearing with me!

Ps, I'm in east texas - I'll update my profile once I'm on my Mac

 

[Jiggz]

Re: 1989 Force 125hp outboard & its rookie owner

So have you removed the head and inspect the gasket and cylinders? At least on those two low compression ones? If you did, can you post pics of the cylinders? The open and inspect step for diagnosing is very critical at this point before going any further.

 

[adamjoelmusic]

Re: 1989 Force 125hp outboard & its rookie owner

So have you removed the head and inspect the gasket and cylinders? At least on those two low compression ones? If you did, can you post pics of the cylinders? The open and inspect step for diagnosing is very critical at this point before going any further.

Here's a quick video with the cover off

1989 force 125hp low compression - bad cylinders - YouTube

 

[MickLovin]

Re: 1989 Force 125hp outboard & its rookie owner

thanks for the video, you Americans always make good commentators :joyous:

 

[Jiggz]

Re: 1989 Force 125hp outboard & its rookie owner

Wow, those two pistons are really in bad shape. However, it was really hard to see how bad the cylinder scoring was. From the shaking you did with the pistons, it is most likely you will have to rebore which means taking the entire powerhead off and disassembling it. However, if the cylinder scoring is not that deep, you can do honing and piston replacement without having to remove and disassemble the powerhead. Of course, you will have to measure the bore after honing to order the correct size pistons. From the look of the #2 it seems the ring got caught on the ports but not really sure about #4. You will need to do a further investigation on what caused the piston ring failures, i.e. lean running, water intrusion, etc.

 

[MickLovin]

Re: 1989 Force 125hp outboard & its rookie owner

All looks like to much work for this little black duck.

 

[Jiggz]

Re: 1989 Force 125hp outboard & its rookie owner

If there is anything that really makes me enjoy this forum is in its ability to train and educate its members self-sustaining in the maintenance of their Force/Chrysler engines, including those with zero experience on O/B engines. It may seem the main purpose of this forum is for troubleshooting and diagnosing, but that is because those are always the two first steps required to do corrective maintenance. I've seen people who are so naive that they cannot even describe or name the parts they hold in their hands and yet with great help from forum members like Frank, Jerry, PNW, etc and some visual aids were able to replace pistons, reeds, head gaskets, etc. Or something that others may perceived to be very complex work and would not even think about doing it in the first place. Of course, this does not always work for everyone.