Re: Compression problem

Sat Nov 05, 2011 11:33 pm

Pull the head, makes everything easier

Re: Compression problem

Sun Nov 06, 2011 4:54 am

As everyone has pointed out it is most likely a valve problem.
However, if you did your compression test with ALL the plugs out, you may want to take another compression test with the other plugs in. this test may show a head gasket failure or not. In my experience, if you have a cylinder with the same compression as its companion , install a plug on the companion and retest, if the cylinder pressure rises you most likely have a head gasket issue.

Re: Compression problem

Sun Nov 06, 2011 5:15 am

Thanks for all the information, I will redo the test with plugs installed and working on the valves this coming week. I have a product called KROIL that I will try on the valves to loosen them. Hopefully that is the problem not the head gasket. I have used this penetrating oil on a lot of old machinery. I have a 1946 Model FB 13-7 grain drill that I used three to make one that I use to plant wheat every year and it worked great on the old rusty bolts. The two donors had set in the weeds for years. I will try to get some pics and post up what I find. Thanks again :thumbsup:

Re: Compression problem

Mon Nov 07, 2011 10:46 pm


I never thought of using the dowel :idea: Now that makes sense and I think I will do that on the next valve I come across. I was constantly in fear of damaging the valve :!:

Re: Compression problem

Wed Nov 09, 2011 6:20 pm

Worked on the little red tractor this week. It now has good compression in 1-2-3 but only about 50 lb on 4. It has a hiss through the carb when turning it over. I have worked the intake valve on #4 up and down for a while with no real change. Sprayed with Kroil and put Marvel Mystery oil in gas and in the cylinder. Have adjusted the valves and rechecked twice.

I don't have a timing light so I did the static setting. The setting was about 1/2" before the first mark. The crank pulley has two notches and I let it pass the first notch and set it on the second. Is this correct? When I go to town again I will see if the parts store has a timing light. The engine sounds solid if I can just get number 4 compression up. I try to fix one problem at a time but it seems that I have had more than one thing going on at a time. I ran the engine for about 15 minutes the other day and it died. It would try to start but die, maybe run 5 to 10 seconds, so today I pulled the distributor again, cleaned the points and reset checked with continuity meter and all worked fine. Put the distributor back on and she cranked. I let her run for 15-20 minutes not very smooth but ran.

Re: Compression problem

Wed Nov 09, 2011 6:34 pm

The 2nd notch on the pulley is the TDC mark. Static timing is usually good enough for the engine. Timing light will tell you if the distributor's mechanical advance is working properly.

My guess is that you will need to remove the head and check the valve and valve seat condition in order to get the compression up on #4.

Order of work.
1) compression.
2) ignition and ignition timing.
3) carburetion / fuel related.

Re: Compression problem

Fri Nov 25, 2011 6:32 pm

Had a little over a week that I was sick! Feeling better now and I worked on my Cub today. Good therapy! I removed the hood and redid the compression check, I have never seen and engine change so much. I checked the last time I worked on it and it averaged 105 lb compression on 1, 2 and 3. 4 had between 30 to 50. Checked again today and lost compression on 2 and had 115 on 1. I am going to the tractor parts store tomorrow and get a head set. Gotta get a valve cover gasket for one of my 861's too, it's got a noisy valve in it!

What type of tool do you guy's recommend to get the valve spring retainers out of the Cub?

Re: Compression problem

Fri Nov 25, 2011 7:22 pm

K-D Tools has one that should work part # KD-379,
I have one just like it that should work.

Bruce T.

Re: Compression problem

Fri Nov 25, 2011 7:34 pm

Bob McCarty wrote:I got one of the C-clamp style spring compressors from SEARS for about $20. You probably know someone you can borrow one from though. Bob
Yup. Sears with adjustable jaws and height.

Search function to of page - - "sears valve spring compressor".

Re: Compression problem

Fri Nov 25, 2011 7:50 pm

Compressor ordered! Thanks guys, I am really looking forward to getting this little tractor running! My Mom has a picture of my with my head stuck in the steering wheel of a '51 Cub that belonged to my Uncle. That was over 55 years ago. If she can find it I will post. :oops:

Re: Compression problem

Sat Nov 26, 2011 7:21 pm

I have the head off and cleaned the tops and all the surface area with a drill and wire brush. Used and old valve tool to get the valves out but because the way it was made it took two of us to manage. I have the valves stuck in a piece of card board to make sure to put them back in the correct guide. The guy that I got this tractor came by today and said that he had owned it for about 30 years. He has kept reasonable maintenance on it, the inside of the engine is remarkably clean.

I jsut checked and the new valve spring compressor should be here the middle or end of next week.

How do you guy's clean the valve stems and guides?

Re: Compression problem

Mon Dec 12, 2011 7:24 pm

I have the engine back together, with a little tinkering I had her running. It was a rough start but after running for a while she smoothed out with a little carb adjustment. The only thing that I didn't like was when I would turn up the throttle she would put out black smoke and run a little rough at fast speed. I am hoping tomorrow to run her some more and maybe she will start to clear up. The longer she ran this evening the better she sounded. :D :D :D :{_}: :{_}: :{_}:

Re: Compression problem

Mon Dec 12, 2011 9:07 pm

BTDT ! After all the things suggested, finally pulled the head - one valve had a chunck out of it! BD to the rescue, did a valve job while I had it opened up and it's good to go!! Just have to keep chasing it down. Dusty B

Re: Compression problem

Thu Dec 15, 2011 6:06 pm

Can't get the cub to run smooth. It will run fairly good at below half throttle and will not adjust. Above half it sputters and blows black smoke. I have changed the float level from book specs to low and it still does the same thing. the guy that had owned it put a kit in the carb. he is mechanically challenged! I made a cardboard cutout for the float adjustment but decied to change the level to get it to run leaner. I also have used the clear hose check for the gas level in the carb. I am going to the tractor parts store again tomorrow for another new set of points and I have put a new set of Champion plugs in today. Static timing set (second notch using ohm meter and turning distributor), plug gap at .25 after valve grind .15, double checked. pLeAsE :help: :lost:

Re: Compression problem

Thu Dec 15, 2011 9:32 pm


Is the the right one from Sears? Craftsman Valve Spring Compressor - Model# 47627