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Triumph Repair/compression


QUESTION: hi i have a 79 spitfire that has set for about 3 years .had to clean webbers up from old gas . got it running but it ran lean in cyl 3&4 . checked compression  and only had 25 to 30 lbs .pulled head and did valve job and check pistons. reinstalled head and now it will not start at all checked compression and all cylinders are low . it has good fire and valve lash is good . valves were seating good on seats so the only thing that i can think is bad rings. just not sure why the compression is low in all cylinders now . what do you think .

ANSWER: Hi Bobby,

It sounds like the compression tests were not done correctly. Do this, Remove all 4 plugs and remove the wires off of the (+) side of the coil. Run the compression tests with the throttle WIDE OPEN. Be sure that on each cylinder test you spin the engine over so that you hit compression at least 6 or 7 times. Any cylinder that is down close to or below 100 PSI will not run. Something is wrong. To determin if that low cylinder is a "Ring" problem run the test again but this time add about 5 sqirts of engine oil in the plug hole just before the test. The compression reading will be higher then the "Dry" test but it should not be more then 10% to 20% higher. If it is a lot higher then that cylinder has a ring problem.
All 4 cylinders should have close to the same compression.

Only when the compression shows good should you proceed to Ignition tests. Fuel tests are always last.

Let me know the results.

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QUESTION: hi  thats the way i did the test. and the wet test did not seem to help much . i am going to get another compression tester and check it again .also the starter is dragging very bad . i have a new starter. i am going to put it on and test with a another compression tester i will let you know what i come up with . thanks for your help

ANSWER: Yes, with a bad compression test dry and wet and after a valve job too makes the compression gauge suspect. Let me know.


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QUESTION: hi howard  tryed the other compression guage and had just about 50lbs on all cylinders car fires but will not run . not sure what to try next car was running before valve job .but now it will not even start on starter fluid . i set valve lash at 010 all valves were checked with valve grinding compound and looked very good . i just cant think that the rings are that bad it was running before and when i pulled the head i put some oil around the piston and it did not drain down .what should i try next ?   thanks /bobby

Hi Bobby,

If you are opening the throttle while runing the compression test and only getting 50 PSI on two different compression gauges there is somethnig drasticly wrong.

Question, was the top of the block "Fly Cut"? (Groove around the top edge of each cylinder bore) If so, you need to be very careful about the head gasket as it should then have an extra thick ring around each cylinder bore and the gasket must me installed with that extra thick ring pointed down.

If however the top of your block is not grooved then you need to be careful NOT to install a gasket with a thick ring. Several of the vendors that sold head gaskets got them mixed up.
To add to the problem some blocks were "Decked" (top of the block resurfaced) and that eliminated the "Fly cut".

All of this does not even count the number of cars that had an engine or block replaced. Either type of block can be installed in any Spitfire and late model MG Midget.

The last and final sure test is to get one of those fittings that screws into the sprak plug hole that has a shop air hose fitting. Then put that piston on TDC of the compression stroke and apply shop air pressure to that cylinder with the car in 4th gear and brakes on. Then open the throttle and listen in the carburetor for any hissing and listen at the tail pipe too. Open the radeator cap and look for any sign of the fluid level raising. This is a 100% test of valves and cooling system head gasket leak. It is no use listening in the oil filler cap because even the best rings in the world will Hiss.

The true ring test is the "Wet" compression test I had gone over before.

The only other thing left is a completely stopped up exhaust system or the cam is radically out of time.

Let me know,


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Howard M. Fitzcharles III


Triumph TR-4 up & Spitfire, and Engine theory


Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

Associate member SAE EAA member

Import Car magazine

ASE Master Auto with L-1 certification up to 2000

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