98' 50 hp Force Low Compression on #1

[dfris2003]

Hey Guys, Need some help here. Iv got this Force 50 hp motor 2 cycle. I checked the compression, #1 is 27 and #2 is 130 psi. Thing runs pretty good. Was just working on timing today and was reading my manual and it suggested to start with a compression test. I have tested this a couple times, to make sure. Same results. This motor did over heat a while back, and had to replace the water pump propellor. Bad Head gasket? It idles a little rough, thats why i was working on it today.


Thanks
Daryl

 

[tater76]

Re: 98' 50 hp Force Low Compression on #1

Sounds like you need to remove the head and inspect #1 for damage. If you remove it carefully the gasket can be saved unless it is the culprit. This is the only easy way to find the reason for the low compression. Have you messed with the carb lately?

 

[dfris2003]

Re: 98' 50 hp Force Low Compression on #1

Thanks tater76. I have messed with the carb. I had an spare and i switch them out. I did have the carb off the motor when i took the compression test. However, After i put the new carb on, and timed my motor, I rechecked the compression. Still Low in #1

 

[tater76]

Re: 98' 50 hp Force Low Compression on #1

The only reason I mention the carb is because there is a chance that it was not adjusted properly. If it was not, you may have run lean on the top cylinder and melted the piston. Pull the head and let us know what you find, and some pics are always helpful.

 

[dfris2003]

Re: 98' 50 hp Force Low Compression on #1

tater76, I got a change to take the head off the motor today. The gasket looked good, but it looks as if the piston has a hole in it and is bent on the edges a bit. The chamber is still nice and smooth, so i think i lucked out some. I added some pics too.

Can i access the piston bolts for the top cylender from the carb side of the motor with out taking off the flywheel?

 

[tater76]

Re: 98' 50 hp Force Low Compression on #1

Looks like a broken ring or rings. If the cylinder is indeed smooth, passes the fingernail test, and has no aluminum rubboff from the piston then you can just replace it. If memory serves me right???? I think it "may" be possible to pull the rod caps from the carb side??? don't quote me on that. I think its only like six bolts to pull of the intake and reed plates so its worth the effort. I have not had a fifty apart for some time now so forgive me on the info. If you need a replacement piston I may have a few? I will look.

 

[dfris2003]

Re: 98' 50 hp Force Low Compression on #1

Thanks tater76,

The cylinder is smooth, not sure what the fingernail test is, you can actually still see the honing? marks on the cylinder walls. What would happen if i missed a small grove or something, in the walls, and put in the new cylinder? Got me a bit worried now. lol

I found a guy on ebay that sells the piston and rings for $124, is this a good value?

 

[tater76]

Re: 98' 50 hp Force Low Compression on #1

The fingernail test is performed simply by dragging your fingernail across the surface of the cylinder. If there are any scores or scratches deep enough that your nail catches in them, it might need oversized. However, if its very minimal scoring a hone job usually cleans up any issues.
If the scoring is too deep and you just replace the piston, it will likely be low on compression. If it were me... I would hone the cylinder lightly, find a good used piston, buy a new set of rings, and install.

$124 is about right for the piston kit, but remember that you will need a press and a special tool to remove and install the wrist pin. That is unless, you go with a Wiseco piston that has a floating wrist pin. You will still need to remove the old piston from the rod with a press, but the install is way easier.

A better option is to find a good used piston and rod combo, replace the rings and install. This could all be easily done in a day. If you want to go the used route I may have a good one.

 

[dfris2003]

Re: 98' 50 hp Force Low Compression on #1

Thanks, its I think used would be easier route. Let me pull the piston and Mic it so I know what size and ill post it.

 

[dfris2003]

Re: 98' 50 hp Force Low Compression on #1

Tater76,

Well I finally got that dang motor apart, hahah. Anyway the rings are shot and melted on the side of the piston. I measured the piston at the end, out side to out side, at the connecting rod end. It measuered 3.366 Inch or 85.49mm

I have looked online and it seems that the standard size is 3.374 so i either measure it wrong, or my device is not as accurate as factory.

Anyway, if you got a piston and rod, give me a price.

Thanks
Daryl

 

[Frank Acampora]

Re: 98' 50 hp Force Low Compression on #1

Daryl: The 98 40 and 50 horse all have 3.375 bore. Pistons are sized to provide adequate clearance for the standard bore so they are slightly undersized. In addition they are cam ground with a major and minor diameter to account for uneven heating in the marine 2 cycle engine.

$124 is expensive. You can get Wiseco pistons from the factory for less and Seirra pistons from NAPA for even less than Wiseco.

 

[tater76]

Re: 98' 50 hp Force Low Compression on #1

Well, turns out my 3.375 piston stock is completely depleted Sorry about that, but if Frank can guide you to a piston kit for less than $124 I would do it. I don't know where he's getting them, but the cheapest I have ever paid is $98+ shipping. That includes the piston, pin, and rings. Maybe he will chime in, as this would be a great resource.

 

[pnwboat]

Re: 98' 50 hp Force Low Compression on #1

Here's a site that has'em for $88.02 + flat rate $15.00 shipping UPS ground.

http://www.outboardparts.com/chrysler/mall/forcepistons.htm

I've used them many times.

This site has'em for $90.00 + $8.75 shipping.

http://www.maxrules.com/fixforcepiston.html

Never ordered from them.

 

[dfris2003]

Re: 98' 50 hp Force Low Compression on #1

Wow, thanks for the info. I do have a couple of questions.

How many gaskets do i need to replace? Head gasket, and ?

Also does anyone have a towershaft for a 98 force 50hp? Mine looks deformed at the top bushings, and has worn them out. Part # 826284.

Last, can i use locktight on bolts? And any special grease or process putting the motor back together?

I do have a manual, just getting field advice.

Thanks
Daryl

 

[dfris2003]

Re: 98' 50 hp Force Low Compression on #1

Bump.....

 

[tater76]

Re: 98' 50 hp Force Low Compression on #1

If the headgasket is free from damage then reuse it, as they are like $40 bucks! If you pulled the intake to remove the piston you will need a new gasket there. If you seperated the case then you may as well buy a powerhead gasket kit $40-$60 bucks. I have a towershaft, but its from an 1985 so not positive on the compatability. As for the locktight and grease on bolts, just follow the manual. If I remember correctly, just the rod cap bolts get locktight, maybe a drop on the top crank bearing where it meets the case.