Compression test - 1 cyclinder lower on 50hp - what's next?

Motor is a 1983 Chrylser 50hp, model# 507H3D

Ok, so once I got my shift linkage fixed and could put the motor in neutral,
I decided to do a compression test. Went to Harbor Freight and bought a cheap, $10.00 test, followed the instructions by removing both plugs, threaded tester into top cyclinder 1st, let it turn over 7-8 times and got 125-130 lbs. Proceeded to the bottom and got 100 lbs. Little odd thing here, but to verify the top cylinder, I went back to it and this time got over 130lbs, closer to 140.

Assuming I did this right, and it read that there was only one way to do it, what's next? I'm about to order a manual (any tips there appreciated), and
I don't might tearing it apart, if I know what to do. Guide me oh wise ones.
And thanks in advance, as this forum has already proven priceless on my 1st repair!

Re: Compression test - 1 cyclinder lower on 50hp - what's next?

Was the engine warmed up? Was the throttle closed?

I would give her a good decarbing and check compression again.

Re: Compression test - 1 cyclinder lower on 50hp - what's next?

Has it been sitting for a while? If so tilt the motor up and add a capfull of 2 cycle oil in the plug holes. Rotate the engine clockwise for a while and recheck compression. I had one that read 110...after adding oil it read 130.

Re: Compression test - 1 cyclinder lower on 50hp - what's next?

You know, it may not have been warm enough. I had ran the thing about1 1/2 , 2 hours prior to doing test for probably 10 minutes then decided to charge the battery. The fact that I'm getting 100 on the lower one seems a little 'off', doesn't it?

Where does one buy this "decarb"? Gotta go to a Westmarine or similar or is that an "auto parts store" purchase?

I'll add the oil too, because I don't know how long it had been sitting prior to me. So you're saying just take the plugs out, pour it in there, right? As for the "closed throttle", it was in neutral, is that not where it should be?

Re: Compression test - 1 cyclinder lower on 50hp - what's next?

The help is getting confusing to me when you move to another matter before present matters are not completed or reported completed. I understand multi-tasking to save time. I?m not a supporter and d/n advise it if you d/n have the personal experience to support it. Good Luck With your experiences. JOW

Re: Compression test - 1 cyclinder lower on 50hp - what's next?

"Decarb" is engine treatment to remove any carbon that may be causing rings to stick, Emoney. I suggest it because a bit of carbon might be lowering the compression in the bottom cylinder. There are several products on the market to do this. "Seafoam" is probably the most popular, but not the only one that works.

Pouring oil into the cylinders will certainly increase the readings, but it will tell you nothing about the health of your engine. A waste of time in my book.

"The help is getting confusing to me when you move to another matter before present matters are not completed or reported completed. I understand multi-tasking to save time. I?m not a supporter and d/n advise it if you d/n have the personal experience to support it. Good Luck With your experiences." JOW

What in the world are you talking about, wickware??

Re: Compression test - 1 cyclinder lower on 50hp - what's next?

Wickware, if you're talking about the shift linkage issue, I thought I made that clear that it was fixed, in that thread and then again in this one. If you're referring to the 'steering issue' then I thought it wiser to check the compression and make sure I didn't need to tear the whole thing apart, before coming up with a way to remove the motor. If not, then I'm a little lost, but will be glad to clarify anything?

Jb, I'll try to find the 'decarb' tomorrow and go through that process and then I'll try and do the compression test again. Since this motor doesn't have a telltale (yet...but it will thanks to that 'sticky' at the top), how can you tell if the water pump is pumping. I see what looks to be a water line running from the top cylinder head that's I'm assuming, coming from the thermostat, but mine is solid black, looks like it's been changed. Is it a major "no-no" to remove that line while it's running to verify the water pump is in fact working? If not, any other suggestions. Also, on the compression test, are you saying I need to the have the Throttle in WOT and if so, that means in gear, correct? My little 50 has a neutral throttle limiter, of course.

I'm ordering a manual tomorrow (want to make sure I get the right one) and I"m assuming a lot of these questions are in there. Sorry to be such a bother, but I'm new at this.:redface:

Re: Compression test - 1 cyclinder lower on 50hp - what's next?

At wallyworld you can get sea foam.It will decarb the cylinders.
Yes remove the hose at the top of the head to check for water.
A comp test can be done with a cold or hot motor.
Remove the plugs,throttle full forward,install tester.Then turn the motor over till the tester wont go any higher.Then do the other piston.
Get a jumper box or remote starter(see pic).That will bypass the neutral safety switch.Watch out for the prop.J

Re: Compression test - 1 cyclinder lower on 50hp - what's next?

Many people advise to put the throttle at WOT for compression testing. I do not. On multi-carburetor engines turned over when cold it is not uncommon for one carb to be choked, putting extra fuel into the flow for one cylinder, which might improve the compression in that cylinder only and produce an error in the balance.

Throttle at idle, gearcase in neutral.

Re: Compression test - 1 cyclinder lower on 50hp - what's next?

I was confused in thinking there were no motor issues due to the quote below in an early post. I?m still interested in the project and would suggest using a 2nd brand of compression gauge if compression seems to be an issue. JOW

Help with Chrysler 50 shift linkage (thread 8/25/10 7:45 AM)


?The little motor runs great and is, in my opinion, rather quiet for an ob of this year. ?

Re: Compression test - 1 cyclinder lower on 50hp - what's next?

Cold/hot,throttle all the way or not.Everyone has their way of doing a compression test.
The readings should be within 5-10# of each other.Any real big difference could be a bad head gasket,scored cylinder,siezed rings,hole in the piston.
Do a good comp test and then follow the diagnostic steps.
Do a de-carb,if that don't help then remove the head gasket and check for damage.J

Re: Compression test - 1 cyclinder lower on 50hp - what's next?

Ok, I'm going to Wally world and getting the seafoam then I will do another compression test. I know for a fact I did it wrong because I had the engine in Neutral the whole time with no throttle. My neutral safety switch has been bypassed by the PO so it shouldn't be an issue. I'll post the new results later this afternoon. The I'll start it and make sure there's water going through that hose. I'm going to do the "telltale conversion" once I figure out how to get that plug off (mines the square head).

It doesn't look as if the motor has ever been apart, so I'm sure the headgasket is the original. I can tell there's a 'newer' gasket on the carberator, but that's about the only one that looks fresh. I'll think I'll order a gasket set regardless as I'm sure the Gulf of Mexico hasn't been the kindest to the seals & gaskets in this thing. By looking under the cover, I don't think maintanence was a high priority in the PO's life. Let's say the compression test comes back normal this time, does everyone agree that I'd be better to tear it down and replace the gaskets anyway? I've been down the "just enough" route years ago with an outboard and it wasn't a fun experience. I'm definitely going to change the impeller once I get my manual. That part I know salt water is notorious for eating.

Thanks again for the help from everybody. And, Wickware, I thought all was ok then I noticed that most everybody's advice on any issue was, "Do a Compression Test" so I figured I had better do one and that's where we are today. Don't worry, I'm pretty simple-minded so we'll have no choice but to go "One Step At A Time", LOL.

Re: Compression test - 1 cyclinder lower on 50hp - what's next?

Ok, now I'm really needing my hand held. So I picked up a bottle of the "Seafoam". From using the 'search' feature it looks like the ideal application is to use a bottle to 1 gallon of gas, kinda like a 'shock treatment'. Problem is, I only have the one tank and it's almost full (10 gallons at least). I've seen someone use a spray bottle (here on the forum) and spray some into the carb. Is this a smart thing or should I pour the bottle into the tank and just let it run?

Re: Compression test - 1 cyclinder lower on 50hp - what's next?

So I haven't done the Seafoam "decarb" yet. Waiting for a little direction there (hint, hint). If I have to, I'll try to find another fuel tank and do the whole, "can to a gallon" trick. I've got the spray bottle standing by.

I did a "Cold motor" compression test, this time with WOT and I got practically the same #s. 135 on the top cylinder and 100 on the bottom. Both cylinders might've had 5 more psi in them, but if one did, they both did. Now I know that a 30+lb difference between the two is bad, and like I said earlier, I'm pretty sure the head gasket is original. And, of course, I'm not doing anything at all until I get the seafoam through there and see what happens. But, my question is, is it normal for a cylinder with a problem to read 100lbs? I ask because most of the "help bad compression test" threads that I've read have all had the problem cylinder between 30-60lbs PSI.
Just curious?

Re: Compression test - 1 cyclinder lower on 50hp - what's next?

Take your fuel hose off behind the bulb, mix up your recipe in a one gallon container - put in your hose in the container ( jug or whatever) squeeze the bulb and do your trick.
jim

Re: Compression test - 1 cyclinder lower on 50hp - what's next?

I have the compression gauges from my 60s ? 90s automotive repair and diagnostic days but I have not run a compression test once on my 1970, 35 HP Chrysler. The engine has never given me an indication since my 1985 purchase that it needed a compression test. It has always idled, powered out of the hole and planned (with 2 and gear or me at about 33 mph). Plus, the seller took me for at least 30 minute + ride on the lake related to the motor and boat. Very unusual for me not to run a comp test for the records at the least. I w/n attempt to tune a car/truck/ etc back then w/o a comp test first if a lack of power or etc dictated the test. I?ll do one at the end of this season to see what I have been missing. I feel I looked at the small engine as I did smaller combustion engines. I only ran a compression test if there was a lack of power/etc as a reason for the test vs a natural on unknown cars/trucks before a major tuning.

Any lack of power or etc that has been noticeable has been cured with cleaning the points vs any plug problems. I agree the compression test can tell you if you have problems a tune-up w/n cure.

Re: Compression test - 1 cyclinder lower on 50hp - what's next?

Thanks, Jam. I thought about that but wanted someone to
'reassure' me, just in case. I'll be seafoaming this evening then!

Wickware, I've been paranoid ever since I did a compression test, so
I'm not sure you should do one...lol. I didn't think I had any problems
until I did mine! But, in my case, I'm sure the issue would've come up once
I was a mile or so away from the house. And, that, is something I
don't want to experience. I've been there years before and it's not a
fun time. My goal this time is to take my time and make absolutely
sure the kinks are ironed out. Now, I'm not naive and don't think anything
can happen. But, for the most part, an ounce of prevention...etc, etc.

Re: Compression test - 1 cyclinder lower on 50hp - what's next?

As I'm at work (avoiding the same, of course) it occured to me that I hadn't mentioned this. When I removed the spark plugs, the top cyclinder plug was very 'black' and the bottom not so much. Does this indicate anything.

Also, may have found a parts motor locally, but I'm torn as to trying to buy it or ordering a complete gastket/seal kit for mine. The one I found has a bad lower unit and I don't know enough about everything else at this point, although I hope to go and see it after work. It seems like if the lower unit
was all that was bad, then a person would be better off having it for all the other parts should something happen, right?

Re: Compression test - 1 cyclinder lower on 50hp - what's next?

Is it essential to run the boat, in the water WOT after using the Seafoam?
I'm assuming I'm to let the boat run through a gallon of gas with the seafoam
mixture, while spraying a small amount right into carberator? I gathered
this from reading other posters & advice they received. Will the plugs be
fouled and should I have new ones ready before the 'on the water blow-out'?

Re: Compression test - 1 cyclinder lower on 50hp - what's next?

You know, Money: You are jumping to confusions. Oil this, Sea-Foam that, compression low etc.--- You have an old engine that has not been run much recently.

It is no secret that I don't think much of Sea-Foam and feel that while it may have some use it also can cause more problems.

Don't go crazy. Water testing will tell you more in one minute than hours in the driveway will.

Devote a day that you will not expect anything good to happen. Don't take the kids or wife.

Assuming it starts in the driveway: Take the thing and put it in the water! Run it but stay close to the dock. See if it gives you any indication of problems like loss of power, lack of idle, or very rough idling. If it runs halfway decently, then run a couple of tanks of 25 to 1 through it. Then recheck compression. Betcha it comes up and is more equal.

If it doesn't run well, THEN get excited.