Low compression on #1 Cylinder (Updated 7/30/08 w/Pics)

[GrindKore]

I just did a compression test on my 1990 FORCE 90 and got following readouts:

Cylinder #1 (top): 56psi
Cylinder #2: 127psi
Cylinder #3: 125psi

The thing is, this motor starts easy, idles well, and gives me descent WOT speed (about 34MPH). The only reason I started poking around with compression was after I installed the tach gage and realized the RPM at WOT is only 3900RPM.

Currently I'm running sea-foam through it hoping carbon buildup on the rings is causing this. However, I'm sure that will not solve my problem. My question is, can a motor with a blown piston perform so good that otherwise I would never suspected any problems?

Also If I take off the cylinder head bolts and remove the plate to inspect cylinders, will I need to replace the gasket?

 

[jerryjerry05]

Re: Low compression on #1 Cylinder

Re: Low compression on #1 Cylinder

Any info would help.How big is your boat? Completely loaded?
Did you do the test more than once?(I'm sure you did)
Spray a heavy oil in the cylinder and do the test again,on all 3 cyl.
Comp sould be 145-150# Your guage might be off.
Two cyl with good comp and one with about 1/2 comp will run.You maybe caught it before you ruined it.
Try Seafoam or Merc Power Tune to remove the carbon.
You will need to buy a new gasket.Make sure to torque the head 20Ft#
Try to decarbon before you remove the head.
Use a piece of wire to inspect the cylinder for grooves in the cylinder walls.
Luck, Jerry

 

[GrindKore]

Re: Low compression on #1 Cylinder

Re: Low compression on #1 Cylinder

I just finished decarbing this motor using 1 can of SeaFoam, the compression readings are as follows:

#1- 67 psi
#2- 115 psi
#3- 127 psi

I repeated the compression test several times and readings were repeatable. I guess the head will have to come off today, I'll post updates with pictures once I get everything removed.

Also, the spark plug do not appear to have any abnormal ammount of deposits or dry. All three plugs look nearly identical with healthy ammount of fuel/oil.

 

[GrindKore]

Re: Low compression on #1 Cylinder

Re: Low compression on #1 Cylinder

Well, unfortunately the pistons are damaged, the #2 piston is heavily pitted from what looks like a piece of ring or other metal debree that has made it's way in to a combustion chamber.

Please look at the pics I have included and let me know what is the best plan of action here.

 

[tjello327]

Re: Low compression on #1 Cylinder (Updated w/Pics)

Re: Low compression on #1 Cylinder (Updated w/Pics)

Looks like it could be a ring but dont overlook your reeds. One could have broke. The pits on the one piston do look like a smaller piece of metal like a broken ring.

Good luck.
I know I need it with my ignition!

 

[Frank Acampora]

Re: Low compression on #1 Cylinder (Updated w/Pics)

Re: Low compression on #1 Cylinder (Updated w/Pics)

Agree---pull the carbs, manifold, and reed plates. See if it ate a reed retaining screw or a reed. Remove all the screws completely and re-install with locktite. Use loctite on the Vee block retaining screws too even though they are outside the manifold and can easily be retightened.

You are going to need to replace at least two pistons. The rough ports can be chamfered and dressed with no ill effects. You will probably need to remove the exhaust chest cover to access them though. Buy yourself a dremel and a carbide bit; some of those cylinder liners are hard as glass.I can not see the center cylinder liner but the other two don't appear to have major scoring. Maybe a simple honing will suffice.

So, assuming that the cylinders only need honing, you will not need to disassemble the engine to repair it. You are going to need say, two pistons, three vee block and manifold combination gaskets, at least one exhaust cover gasket, and for good measure, a head gasket.

If the engine has never been rebuilt, those would be stock 3.375 bore pistons. I recommend Wiseco pistons as they are much easier to install than stock.--Better rings too.

 

[GrindKore]

Re: Low compression on #1 Cylinder (Updated w/Pics)

Re: Low compression on #1 Cylinder (Updated w/Pics)

I appreciate the feedback. The cylinder walls feel smooth to touch, I do not see any deep groves. Can you guys point me to a thread or perhaps describe the honing process? Also, what special tools will I need for this job?

 

[Frank Acampora]

Re: Low compression on #1 Cylinder (Updated w/Pics)

Re: Low compression on #1 Cylinder (Updated w/Pics)

Buy a three stone hone at Sears. Chuck it in a hand drill, compress the legs and set in in the cylinder. Then tighten the top pressure nut to press the stoned against the cylinder walls. Use plenty of oil. Now, at SLOW drill speed move the hone fully up and down in the bore. The object is to have the cross-hatch marks at about 60 degrees to each other. It takes a bit of experience to get it right-- but don't worry, you will learn. Be careful not to hit the land at the bottom of the cylinder.

Do not remove too much material. The object of honing is to "Break the glaze" and allow the new rings to "seat" properly. You are also leveling the surface and removing light scoring and deposits. If there is any rubbed-off aluminum in the cylinder, use a heavy duty razor and scrape out most of it before honing. After honing, very carefully clean the cylinders paying special attention to the bypass and exhaust ports where oil and grit will accumulate and then blow through the engine when running. Wipe until no black comes off on a clean white cloth. Since you will be generating metal chips while dressing the exhaust ports and grit when honing, be very fastidious about cleaning. When dressing the exhaust ports (prior to honing) stuff rags in the bottom of the cylinders to keep chips from going down by the crankshaft.

You will need hand tools, a 1/4 inch drive 12 point 1/4 inch socket (for the con-rod big end bolts), a torque wrench, access to a bench press (to press out the wrist pins), and patience.

Within the past two weeks or so, I have posted instructions for replacing a piston without disassembling the engine. Use the search function for those threads.

 

[GrindKore]

Re: Low compression on #1 Cylinder (Updated w/Pics)

Re: Low compression on #1 Cylinder (Updated w/Pics)

Thanks Frank, I have read your threads and will follow directions you have there. Interesting enough both Clymer and SELOC examples are suggesting to detach the power-head and perform this procedure on the bench. Do you have any comments as to why they choose that route?

 

[GrindKore]

Re: Low compression on #1 Cylinder (Updated w/Pics)

Re: Low compression on #1 Cylinder (Updated w/Pics)

So far I sourced following replacement parts on outboardparts.com

3x CHRSYLER / FORCE STANDARD SIZE PISTON
3x CHRYSLER / FORCE WRIST PIN BEARING WITH WASHERS
1x CHRYSLER / FORCE GASKET KIT 3 CYLINDER WITH HEAD GASKET

Total: $336.40

Tomorrow I will take apart the exhaust manifold, carbs, crank case cover, and will attempt to remove all three pistons. I'm hoping the damage is contained, hopefully no more surprises are waiting for me.

 

[Frank Acampora]

Re: Low compression on #1 Cylinder (Updated w/Pics)

Re: Low compression on #1 Cylinder (Updated w/Pics)

Both seloc and Clymers do it on the bench because if you need to bore a cylinder, the engine must be disassembled. Also, remember that you are going to generate a bit of grit and metal from the operations you will be doing. On the bench with the engine disassembled, it is quite easy to clean the block. But notice that both these manuals are not in the real world. They use new engines as examples so disassembly is easy--Not so easy on an engine that has seen water for 20 years.

Doing it with the block assembled means you MUST be fanatic about not letting grit get to the crank area and about cleaning by hand afterwards.

It is a big pain to get the block off the leg because almost all the time, the mounting studs are corroded into the holes in the leg. But if you have the time it is preferable from a cleanliness standpoint to disassemble the block.

Also. Clymers does not show a procedure for reassembling the roller bearings and big end of the rod while the block is still assembled. That can be a bit frustrating--it is way easier with the block disassembled. However, from a time standpoint, if you really need the engine, then that is the way to go.

For example: I recently replaced a piston in a 4 cylinder block for a fellow. He came at 9 am on Saturday. I replaced the piston, found he had a bad lower motor mount and replaced that, found all his reed blocks and stop plate screws were loose so I also tightened them. Even though the engine did not cooperate --rollers just didn't want to go in properly, corroded screws snapped and needed to be drilled, etc.--I had the engine back together and running before 5 pm. by 5:30 we were on the water testing the engine. And I felt bad because I told him the piston replacement would be about 3 hours.

Now, Wiseco pistons with rings and wrist poins are about 125 each and the required bearing kit for the rod small end is another 14 bucks. Head gasket is around 27 bucks. Then add some shipping and cost is similar but it might pay you to investigate them. As I said, they are much easier to install than stock pistons. The local distribution warehouse is in Mentor, Ohio. 800 321-1364

Now, you have some of the pros and cons. After this, if you do decide to invest the 10-15 hours to disassemble the engine to do the work and reassemble, then think about using your dremel to square and streamline the ports in the cylinders. Takes about 2 hours per cylinder. You will need to chamfer them anyway to correct ring damage and prevent rings from catching again. This way you will pick up a few more ponies. Maybe up to 5 MPH more.

If you want to see an example of porting on an old 90 Chrysler, go to The Chrysler Crew. Join. Scroll down to the questions forum and click on it. Then at the left side click on photo albums and search for Frank's boats.

 

[GrindKore]

Re: Low compression on #1 Cylinder (Updated w/Pics)

Re: Low compression on #1 Cylinder (Updated w/Pics)

What tool do you use to reach bottom bolts on exhaust manifold? My standard 7/16 socket and wrench do not fit between cowling wall and there is no room for regular wrench to turn.

 

[GrindKore]

Re: Low compression on #1 Cylinder (Updated w/Pics)

Re: Low compression on #1 Cylinder (Updated w/Pics)

Well, I have removed the carburetors and reed valve assemblies. The good news all reed valve screws are in place, looks like the damage on #2 cylinder was caused by something else.

Can anyone tell me the name of the socket that will work on the connecting rod end cap bolts? When I call NAPA I have no way of explaining what I need.
Frank has mentioned "12 point 1/4 inch socket ", however the guy on the phone had no clue what it was. Perhaps there is a brand name of sockets that would be more familiar to auto parts clerks.

 

[Reboot11133]

Re: Low compression on #1 Cylinder (Updated 7/28/08 w/Pics)

Re: Low compression on #1 Cylinder (Updated 7/28/08 w/Pics)

Frank is correct. It is a 12 point 1/4 inch socket and I had a hell of a time finding one. I ended up borrowing from a friend because I couldn't buy it anywhere. I am sure Snap On or Mac or some other specialty tool company will have it.

 

[Daphne444]

Re: Low compression on #1 Cylinder (Updated 7/28/08 w/Pics)

Re: Low compression on #1 Cylinder (Updated 7/28/08 w/Pics)

You can find a 12-point 1/4in with 1/4in drive at sears. (I just got one the other day to replace a couple of pistons.) I had the same damage at the exhaust ports, lower rings were broken.

Heed Franks advice on slightly chamfering the exhaust ports, I did a little on mine but probably not enough. I'm praying that they will not catch on the new pistons.

When you go to remove the rod big end cap and recover the cages and rollers I found it easier to stuff a couple of clean rags around the rod end in the reed openings. This prevented the rollers from falling down around the crank and having to try a fish them out through the cylinders. The rags kept them all in the reed opening where I could easily retrieve all 16.

 

[GrindKore]

Re: Low compression on #1 Cylinder (Updated 7/28/08 w/Pics)

Re: Low compression on #1 Cylinder (Updated 7/28/08 w/Pics)

I have successfully removed all pistons and can account for all pin rollers. Thanks to everyone for your suggestions. I did find 1/4" 12 point socket at Sears.

As you can see from the picture, the rings are shot on all three pistons. I still do not understand how this motor kept working with such extensive ring and piston damage.

My next question is; What is the best way to remove piston pin? I do not have a bench press or know anyone who has one.

By the way, per Frank's advice I have ordered three new WISECO pistons and bearing kits along with the gasket kit. Hopefully replacement pistons will get here by Friday. On a brighter side the cylinder walls are surprisingly in good shape, hopefully light honing will do the trick.

 

[Frank Acampora]

Re: Low compression on #1 Cylinder (Updated 7/28/08 w/Pics)

Re: Low compression on #1 Cylinder (Updated 7/28/08 w/Pics)

Since you ordered Wiseco pistons and are not going to use the wrist pins, needles, or keepers, Just take a fine adjustment tool and beat them out with a drift. It won't damage the small end of the rods and you don't care about the needles. Just hold the drift with a vise-grips. If you slip with 3 pound psychology, you are going to sing a lot of nasty lyrics like a rapper.

If you have a 2 ton bottle jack and can brace it in some sort of frame, that will usually suffice to press out the pins---Or, call in a favor at the local Pep Boys. Slip the guy some beer money to press 'em out for you.

I think you will be pleasantly surprised at the quality of the Wiseco pistons.

 

[GrindKore]

Re: Low compression on #1 Cylinder (Updated 7/28/08 w/Pics)

Re: Low compression on #1 Cylinder (Updated 7/28/08 w/Pics)

I'm setting up to do the cylinder honing job today. I have searched the forum threads regarding the honing process and have derived the following knowledge:

1) Do not pull honing stones out more than 1/4 way out.
2) Use low RPM on the drill while maintaining constant in-out motion to archive 45 to 60 degree cross thatch.
3) Use oil to catch grit.
4) Clean everything religiously.

Is there anything else I should or should not do? Also, can I use regular 2 stroke TCW-3 oil as honing lubricant?

 

[GrindKore]

Re: Low compression on #1 Cylinder (Updated 7/28/08 w/Pics)

Re: Low compression on #1 Cylinder (Updated 7/28/08 w/Pics)

The honing job has been completed. I have also dressed the sharp edges on all intake and exhaust ports prior to honing. I ended up using the 10-W90 (gear lube oil), it is just the right consistency to stick to the cylinder walls and catch the grit that comes off during the honing process.

Here is the result (this is my first time, so I'm a noob when it comes to engine rebuilds):

After honing and cleaning up, I have applied liberal amount of WD40 to prevent atmospheric moisture from attacking freshly exposed steel. New pistons are on the way, hopefully I'll have them here in couple of days.

I have another problem now. My wife is accusing me of caressing my other woman (the boat) more then her, I don't know what to do now.

 

[GrindKore]

Re: Low compression on #1 Cylinder (Updated 7/30/08 w/Pics)

I'm happy to report that the motor works very well now. I finished assembly last night, and ran her on the muffs if the driveway for about 45 minutes at 1200 RPM and rich fuel mixture. Once fuel pump was primed with fuel, she started right up after about 3 seconds of choke. Initially I set the carbs to 1-1/2 turns from seated to give her extra rich fuel/air. After about 30 minute idle on rich mixture, I leaned the carbs back to normal (about 1-1/8 from seated) and she is idling and throttling up beautifully. She also starts up with less than 1/2 second of ignition after motor has warmed up.

The new compression reading are as follows:

#1 - 118psi
#2 - 122psi
#3 - 125psi

I do realize these are not ideal compression readings, however compared to what it was before this will do. It is likely to get all the power back from this motor, I will need to bore it and use next size .010 pistons. This is not something I want to do on a 18 year old motor, so this should be good enough.

Later today I'm going to take her out on the lake for a more thorough test, I'll let you guys know what happened.

BTW, thank you all for your feedback and help. Frank, I owe you a 6 pack.