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MG MGB Technical - advice after compression test

Please I need advice. What means follow results for my compressiontest?
I do the test dry (1) and wet (2)

1 2

Cyl 1 110 125
Cyl 2 150 175
Cyl 3 145 175
Cyl 4 125 150

How can I solve the problem(s)? Valve, cylinderhead or pistonrings??? (Engine have 2500 miles after rebuild...)

Thanks to all and sorry for my not so good (bad) english...

Kind regards from Belgium and my MGA (with 18V MGB engine)

Meersman Pol
Meersman Paul

Was engine hot, warm or ambient? Engine rebuild means different things to different people. What was actually done (e.g., to cylinders, pistons, cam, head, valves, ..., etc.)?
Steve Buchina

Engine was hot by the test. Complete rebuild by a engineshop in the UK... (i dont have see it!)
Meersman Paul

It looks like bad rings or that the rings haven't seated fully yet. First call the engine shop and see what they think. If you don't get an answer, you may need to remove the head and see if it really was rebuilt. While this won't let you see the rings you can tell if it was bored and honed. You can also check if the valves were properly ground. Don't like to say this but sometimes you don't get what you payed for.
John H

I understand John what you mean: "Don't like to say this but sometimes you don't get what you payed for" thanks
Meersman Paul

Suggest finding out what was done to engine. Invoice might (should) stipulate. If not, contact shop and request listing of work done (you paid for it) and new parts installed.

Were new pistons installed to match cylinder bore? Was a new cam installed with new lifters?

Check your valve/rocker clearance. Adjust if necessary and recheck compression.

What kind of compression tester are you using (push type or threaded)? Might add, take your readings then do it again. Do readings repeat?
Steve Buchina

Was the Compression tester you used a rubber cone type or a screw in type. There is a little skill in correct use, the smallest leak can upset a reading. it may pay to get a second opinion before deciding a coarse of action.
The screw in type is by far the best.
DENIS4

Paul, I'm curious if your readings are in pounds per square inch or in kilo's ? If it's pounds then the center 150, 145 lb readings would be reasonable. The outer two cylinder readings are not within an acceptable percentage of the two center cylinders. The increase in the wet readings indicates faulty ring seal. Were all the readings taken with the carb plates wide open?

LaVerne
LED DOWNEY

Cylinder 1 looks like very bad rings or bore, or a bad valve/seat. 2 and 3 are fair but should really be the same after that mileage, as long as you haven't been using synthetic oil. Even then a few dozen miles of serious accelleration and speed may bed things in a bit better. Cylinder 4 could also be bad rings or valves. Valves can generally be detected by a beat in the exhaust if it is an exhaust valve or in the inlet if it is an inlet. For an exhaust valve if you remove each plug lead in turn and still get a single exhaust beat but of a different sound then that is the cylinder with the problem. If you get a double beat then it is a different cylinder. In any case if removing some plug leads causes not so much of a drop in idle speed as others, the ones that result in the smaller drop in idle indicate that cylinder isn't doing as much work as the others, i.e. they could have the rings/inlet valve problem.

Your English is fine, dare I say better than some for whom it is a first language. I was in Belgium last month for the 90th Anniversary of the battle of Passchendaele. I see you have an Army email address, there were lots of military at Tyne Cot on Thursday 12th for the visit of our respective Queens, were you there?
Paul Hunt 2

To all:

The values are in PSI. I do the test with a "screw in" type tester. I do the test two times on two different days with the same results. I think to remove the cylinderhead next month. I give you feet back if I have more news about my problem (good or bad). Long live the English Cars any way...
meersp

To P Hunt:

No Paul I was not there at the 90th Anniversary of the battle of Passchendaele. A small delegation from my corps was there, I have duty... Next time we meet each other (maby 100 th Anniversary)and drink a great original Belgian beer together. Kind regards Pol
Meersman Paul

I copied this from Peter Burgess website.

http://www.mgcars.org.uk/peterburgess/page45.html

After 2500 miles the rings and bores may just not be bedded in correctly yet.......


Running in a new engine.

• Do not let the engine labour...cruise up hills in a lower gear.
• Do not hold the engine in higher gears to see what it will rev to.
• Until the engine has bedded in the friction will be high between the rings and the bores.
Excessive heat build up can soften the rings and damage the bores.
• Drive the car fairly spiritedly in the lower gears...this will aid bedding in.
Bursts of 5000 to 6000 rpm will not hurt the engine in the first two gears.
• Keep an eye on your oil level...running in oil is thin!
• Change the running in oil to the correct grade of oil when you have reached the
mileage recommended by your engine builder/oil supplier.

Running in oil

• Modern oils are excellent at preventing engine wear..........
unfortunately!......you need the engine to wear in a controlled manner.
Running in oil is usually a straight 30 weight oil with no additives.
• If the engine is run in using oil with additives there is a good chance it
will burn oil for the rest of it's life! The additives prevent the rings bedding into the bores,
the high spots in the bores bend over and work harden......these little pockets retain
oil which burns when exposed to the burning mixture!

FWIW
Chris Cooper

This thread was discussed between 09/08/2007 and 11/08/2007

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