Markings on Pistons

The Cub Club -- Questions and answers to all of your Cub related issues.
Forum rules
Notice: For sale and wanted posts are not allowed in this forum. Please use our free classifieds or one of our site sponsors for your tractor and parts needs.
aball36
Posts: 25
Joined: Wed Jan 15, 2020 9:36 pm
Zip Code: 48609
Tractors Owned: 1949 Farmall Cub
1951 Farmall Cub

Markings on Pistons

Postby aball36 » Wed Oct 06, 2021 10:14 pm

On the 49 cub, after cleaning off the top of the pistons, the markings became visible. There is a ".040-S" marking which I am assuming means one of the previous owners put in pistons that are 0.040 oversized. There is also another stamp that appears to say "97B", what might that mean?

Thanks,

Adam
Attachments
cub5.JPG

inairam
5+ Years
5+ Years
Posts: 2098
Joined: Wed Jul 08, 2015 10:24 am
Zip Code: 19342
Tractors Owned: 1948 6v - Dozer
1949 with kub klipper belly mower. mag 6v - Mom
1950 with plow, 54 blade, mott mag 6v - Roxanne
1953 54 blade, c22, wood 42 6v
1957 6v - barn Queen
1965 lo-boy with c-3 mower 12 v - Loboy
1974 Horse II 12 v c-2
1975 with woods 42-6 12 v - Horse
1979 long strip 12 v stuck engine
130 with international 1000 loader 6 v
1969 140 with bush hog tow behind mower 12 v
Memberships: Rough and Tumble Engineers Historical Association;Chapter 8 IH Collectors; IH Collectors Worldwide
Circle of Safety: Y
Location: Glen Mills PA

Re: Markings on Pistons

Postby inairam » Thu Oct 07, 2021 7:57 pm

The engine looks good. If it has oversized pistons it was rebuilt. Did you do a compression test before you pulled the head? That just may need a new gasket and the replacement head and you are in business.
When you only have 9 horsepower you need to know the names of all of the ponies!

aball36
Posts: 25
Joined: Wed Jan 15, 2020 9:36 pm
Zip Code: 48609
Tractors Owned: 1949 Farmall Cub
1951 Farmall Cub

Re: Markings on Pistons

Postby aball36 » Fri Oct 08, 2021 5:09 am

Thanks for the reply. I did run a compression test first. It ranged from. 50psi to 67psi on the 4 cylinders. Based on some posts I read on this forum, it sounded like compression should have been up around 100psi. I was thinking of pulling the valves out just to look at them as long as I have gone this far.

inairam
5+ Years
5+ Years
Posts: 2098
Joined: Wed Jul 08, 2015 10:24 am
Zip Code: 19342
Tractors Owned: 1948 6v - Dozer
1949 with kub klipper belly mower. mag 6v - Mom
1950 with plow, 54 blade, mott mag 6v - Roxanne
1953 54 blade, c22, wood 42 6v
1957 6v - barn Queen
1965 lo-boy with c-3 mower 12 v - Loboy
1974 Horse II 12 v c-2
1975 with woods 42-6 12 v - Horse
1979 long strip 12 v stuck engine
130 with international 1000 loader 6 v
1969 140 with bush hog tow behind mower 12 v
Memberships: Rough and Tumble Engineers Historical Association;Chapter 8 IH Collectors; IH Collectors Worldwide
Circle of Safety: Y
Location: Glen Mills PA

Re: Markings on Pistons

Postby inairam » Fri Oct 08, 2021 5:40 am

Did it run? At those numbers I do not think it would start. The block does not look that bad.

Did you adjust the valves before the compression test?
Did you remove all of the spark plugs and open or remove the carb?
When you only have 9 horsepower you need to know the names of all of the ponies!

tst
10+ Years
10+ Years
Posts: 4425
Joined: Tue Jan 12, 2010 2:08 pm
Zip Code: 12514
Circle of Safety: Y

Re: Markings on Pistons

Postby tst » Fri Oct 08, 2021 8:02 am

engine is .040 oversize pistons, suspect 97B is may be a production date ? make sure your compression gauge is good, that engine does not look that bad for those low a readings

User avatar
ricky racer
10+ Years
10+ Years
Posts: 5383
Joined: Wed Sep 12, 2007 8:40 pm
Zip Code: 49120
Circle of Safety: Y
Location: Niles / Buchanan, Michigan

Re: Markings on Pistons

Postby ricky racer » Fri Oct 08, 2021 12:30 pm

It doesn't matter what the engine looks like. With the low compression numbers, either the valves weren't seating or the rings or cylinders are worn. I'd measure the bores or drop a piston out, pull a ring off and put it in the bore to measure the end gap if the valves look like they've been seating.
Check the valve clearance and adjust as needed. If the valves were out of adjustment enough that they weren't fully closing, you can rest assured that's where the low numbers are coming from.
1929 Farmall Regular
1935 John Deere B
1937 John Deere A
1941 John Deere H
1952 John Deere B
1953 Farmall Cub

aball36
Posts: 25
Joined: Wed Jan 15, 2020 9:36 pm
Zip Code: 48609
Tractors Owned: 1949 Farmall Cub
1951 Farmall Cub

Re: Markings on Pistons

Postby aball36 » Sat Oct 09, 2021 7:03 am

Thanks for the messages and confirmation on the oversize pistons.

For background, the tractor was gradually starting to run worse and worse over the last year and I thought I would check compression as long as I was starting to get deeper under the hood. When I gave up on it about 6 months ago, I could not get it started and got sick of charging the battery attempting to start it.

Unfortunately I did not read up on the compression test topic very much before doing the test and based on some of the responses, I am starting realize the test values may not have told the whole story without doing it the proper way. Live and learn the hard way. I went to Harbor Freight, bought one of their tester gizmos and starting popping one plug at a time testing each cylinder dry. I did not do any wet testing and didn't take the carb off as the one inariam had asked. Once I finally managed to get the head off, the block was rough looking, charred black, etc. before I wire wheeled it. I am surprised at how nice it did clean up however and was also surprised that one of the previous owners had put in oversize pistons.

Adam

User avatar
Glen
5+ Years
5+ Years
Posts: 5109
Joined: Mon Mar 19, 2012 7:33 pm
Zip Code: 00000
Tractors Owned: 1956 Farmall Cub with Fast Hitch, F-11 plow, Disc, Cultivator, Cub-22 mower
Circle of Safety: Y
Location: Wa.

Re: Markings on Pistons

Postby Glen » Sat Oct 09, 2021 8:45 pm

Hi,
You don't have to remove the carburetor to do a compression test, just open the throttle fully, so the engine can get air.
Have all 4 spark plugs out of the engine at the same time.
Charge the battery fully for the test, and use the starter.

The Cub service manual says a Cub engine has 120 lbs of compression.
That is probably for a new engine. 90 lbs or more is ok, they have said on here.

I'm not sure if the engine ran while you have owned the Cub, or if it smoked when running.
Blue smoke is usually from burning oil.

Since the head is off, you could try moving the pistons side to side in the cylinders and see if they move, or are loose fitting in the cylinders.

You could also measure the clearance of the pistons in the cylinders, that will give us some idea of the wear it has.
Use a flat feeler gauge set, and push them gently down between each piston and cylinder wall.
Use as thick a feeler gauge as will go in the gap.

Do that with the pistons slightly down from the top of the cylinders, then turn the engine so they are down farther, and measure again.
Write down the measurements, so there is a record.

If it did run, and the results of the clearance measuring are good, and the engine has been rebored in the past, you could try putting on another head, and run the engine, and put in an oil additive, and see if the compression improves over time.
It is easier than rebuilding the engine.

They say on here to put Seafoam oil additive in the engine oil.
They sell it at auto parts stores.
Several people on here that used it said that it helped a lot.
They say on here to make the engine work while using the additive.
If the piston rings are stuck, it can help free them.

One of the experts on here said to use the additive for 2 oil change periods.
The 1955 Cub operator's manual says to change the oil every 150 hours of use.
If the rings are wornout, the seafoam won't help much. :)

Clemsonfor
501 Club
501 Club
Posts: 707
Joined: Sun Nov 10, 2019 5:14 pm
Zip Code: 29848
Tractors Owned: Yanmar YM2000
Yanmar YM186 (non running)
1952 Farmall Cub
Circle of Safety: Y
Location: Greenwood County SC

Re: Markings on Pistons

Postby Clemsonfor » Sun Oct 10, 2021 8:52 pm

As good as that engine looks at least I would make sure the valves are free. Put a new head on it and run it if it will start and put a load on it for a few hours to see if it comes around. As bad as you said it was I wouldn't be surprised but it has stuck rings.

User avatar
Glen
5+ Years
5+ Years
Posts: 5109
Joined: Mon Mar 19, 2012 7:33 pm
Zip Code: 00000
Tractors Owned: 1956 Farmall Cub with Fast Hitch, F-11 plow, Disc, Cultivator, Cub-22 mower
Circle of Safety: Y
Location: Wa.

Re: Markings on Pistons

Postby Glen » Sun Oct 10, 2021 11:15 pm

Hi,
Below is a page from the Cub and LoBoy service manual showing the piston clearance in the cylinders.
When new the clearances are less than .003", so you would be using feeler gauges that can bend to fit in the curved cylinder.
It says skirt clearance bottom, so there's no way to measure the lower part of the pistons from the top, with the rings in place.
The top of the pistons that you can get to might be a different size than down farther, so maybe the only check you can do is moving the pistons side to side in the cylinders.


http://www.farmallcub.info/manuals/gss- ... 001-05.jpg


  • Similar Topics
    Replies
    Views
    Last post
  • Pistons
    by jsfarmall » Mon Jun 29, 2020 4:57 am » in Farmall Cub
    2
    276
    by jsfarmall
    Mon Jun 29, 2020 4:33 pm
  • Pistons
    by john2189 » Sat Dec 07, 2019 2:11 pm » in Farmall Cub
    3
    346
    by tst
    Sun Dec 08, 2019 5:12 pm

Return to “Farmall Cub”

Who is online

Users browsing this forum: Glen and 4 guests