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MG TD TF 1500 - Low compression

I am to the point in my restoration to get the motor started. This motor was rebuilt in 2009 and has about 2500 miles on it. It was running fine when it went into storage in 2014.

Prior to the startup, I ran a compression test. Here is what I got
1 = 90
2 = 125
3 = 75
4 = 75

I put a few squirts of oil in each cylinder, put the plugs back in, and turned the motor over a few times.

Next compression test

1 = 110
2 = 170
3 = 120
4 = 135

Valves are fully opening and I don't see any sticking

My thoughts are that 1,3, and 7 were open and developed rust on the valve face and are not closing completely (I did set the valves at 17 prior to the compression test)

I am thinking this will resolve itself with starting the motor, but would appreciate input from others.



Bruce Cunha

I had an XPAG here that had been sitting for 40 years. Had the same thing as you are seeing. I sprayed the hell out of the ports both in and out with WD40 and it didn't take much running to get some decent numbers with doing nothing more. I can't say whether it will remedy your issues Bruce.
L E D LaVerne

Yep/ could be little pieces of carbon or slight rust film on the valve seats
They all came up 'about' the same amount with the oil in there so i'd say the rings are sealing ok, the raised compression is because of the amount of oil added---I'm betting on dirty/contaminated valves/seats
If it's only done 2500ml. on it and was running ok, I'd take the punt on it---It's amazing what a good run will clean up---It'll be ok as is.
willy
William Revit

That was what I was thinking. Bill Chasser suggested something we used to do when I was younger. Spraying Marvel Mystery oil in the carb once running.

I still remember using chemtune on our cars as a teenager. It smoked out the neighborhood when you poured it down the carb.
Bruce Cunha

Wouldn't bother pouring too much 'stuff' into your engine, a good run is the answer.
William Revit

Give it the benefit of the doubt. With oil in the cylinders, it likely has improved just setting. Leave plugs out and roll it over freely a bunch of times (don't stress starter out). Let it take a deep breathe and breathe out.

Old oil sticks rings in the grooves. (I'm dealing with an overheat/low compression rebuild as we speak). With merely 2500 miles on a rebuild, it certainly isn't worn out.

You have enough compression to start it and let it heat up. Valves will clamp shut and rings loosen/expand to the bore. You should be good to go. Every start will be better than the previous.

ENJOY!!!
JIM N

I got the engine started and used Chem Took piston cleaner. Your supposed to pour it into the carb with the engine running. So I used a spray bottle and put it into the SU's with the idle set up.

Compression is now

1 = 139
2 = 150
3 = 146
4 = 150

Bruce Cunha

This thread was discussed between 09/01/2024 and 21/01/2024

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