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MG MGB Technical - Compression iisue?

The adventure continues......I decided to do a compression test for a benchmark and found puzzling results. #1-210, #2-200, #3-170, #4-170. Should I be concerned? Is not 170 ideal? All of the plugs wer/are a nice brownish color. Should I be concerned? Thanks, Tom
Tom

200 is way too high. Perhaps you have several cc's of carbon deposit, or the head /block has been skimmed, or even the valve timing is off ....
Art Pearse

Thanks Art, if I pull the head, what type of head gasket is best? Tom
Tom in gloomy upstate NY

Hello Tom,

Payen previously Halls CK664 Hi-comp with head gasket AK660 in it or consider copper gasket,

Cheers,

Jean Guy Catford

I see that Moss' price is less for copper than it is for the Payen brand. Which i sbetter? Thanks. Tom
Tom

Hi Tom

We have had the most success with Payen composite black head gaskets, copper ones are less well known make perhaps and also need careful retorqueing whereas the composite one is single torque.

Peter
peter burgess

Hey Guys, I got the head off and found that the headgasket had given up between # 3 & # 4 in addition to leaking into the water jacket. The head measures 78.24mm and the book calls for 80.25 minimum. That accounts for high compression readings on 1 & 2 and only 170 on 3 & 4. That being said, can a standard motor put up with higher compression? Should a copper head gasket br used? Should I seek a new head? Thanks, Tom

Oh yeah, whar is the best way to clean the mating surfaces? Tom
Tom

Hello,


Yes a motor can have higher comp. but it must be in good order with h-quality parts to support that. As the head seems to be skinned you dont have a margin now. In such case I would select copper gasket.

Cleaning surface. Be careful as cast iron is a soft material. I used often a putty knife( metal type) to remove most of old gasket and 120 sand paper to finish cleaning. Be careful to avoid any debris in water circulatiing passages and inside cylinder.

Cheers,

Jean G.
Jean Guy Catford

I forgot,

There is this co. that could make thicker gasket to correct things

http://www.headgasket.com/index.html
Jean Guy Catford

Tom-
Because of these differing coefficients of expansion, a copper cylinder head gasket should never be used in combination with a cast iron engine block and an aluminum alloy cylinder head. Racers like copper cylinder head gaskets for two reasons: First, because they have high crush resistance, thus permitting the application of higher levels of torque onto the cylinder head stud nuts in order to deal with higher pressure levels of both compression and combustion. Second, because they frequently tear down their engines for inspection. This being the case, they do not want to have to spend time scraping bits of torn fiber gasket from the mating surfaces. Beyond those two advantages, copper cylinder head gaskets are obsolete. Certainly the break-in procedure for them can be challenging. Many of these copper gaskets have the letters ‘DV’ stamped onto them which stands for ‘Double Varnish’. These varnished gaskets require that run the engine be run without coolant until the cylinder head becomes hot enough for the varnish to soften and form a seal, then left to cool down for several hours, or, ideally, overnight. Of course, the trick is to reach the appropriate temperature without exceeding it and risking damage to the valve seats or the seizure of a piston.

While today’s sealants are excellent and today’s modern cylinder head gaskets possess greater compressibility than those of the past, they can compensate for warped mating surfaces only to a very limited degree. Instead, use either a Payen or a Fel-Pro cylinder head gasket or one that is marked FRONT/TOP, so installation is a straightforward affair. These gaskets are resin-impregnated, have copper sealing rings to better resist excessive crush pressures, and require no additional sealing coatings as they are surface-coated for microsealing. Best of all, they provide a clean release upon removal. They are also particularly appropriate for use on engines that have been converted to aluminum alloy heads as they handle the differing coefficients of expansion of a cast iron engine block and an aluminum alloy cylinder head quite well. These gaskets seal by heat-bonding to the mating surfaces of the cylinder head and the engine block. The resin softens when it gets hot and makes a better seal. If the mating surfaces are not scrupulously clean, or if you allow the coolant to pressurize before the bonding has fully taken place, then the resin-impregnated gasket will not bond properly to the mating surfaces and subsequent leaks will be more likely. Consequently, you should run the engine without any coolant in it until the engine gets hot so that a good bond can be achieved. While doing so, the V-belt that drives the coolant pump should be removed so that the seal of the coolant pump will not be damaged by its shaft running against it without the benefit of the lubricants contained in the coolant.
Steve S.

Steve ,

I missed something here. Tom spoke about a "standard motor", which have cast iron block and head. In such case copper willl be a good choice.
If you consult web site I mentioned earlier you will find installation procedure are not so demanding.

Cheers,

Jean G.
Jean Guy Catford

OK guys, thanks for the input. I am going with a "dry" Payen gasket. Do I need to re-torque after the initial run in? 9 With NO coolant?)
Tom in springy upstate NY

Tom,

I installed a Payen gasket on my standard 69 18GG.

I did the initial seating-in running the car with clear water as the coolant for 500 miles then replaced it with anti-freeze/coolant. That to avoid/lessen the risk of the glycol-based "slip" factor defeating the sealing of the gasket surfaces to the block/head.

I have not needed to re-torque the head so have not done so. I believe Payen gaskets are designed to not need it.

Regards
Roger
Roger T

Tom, you need to figure out your compression ratio. There has been removal from the head. Maybe the block too - do the pistons stick up at all? If you know the original head volume and piston style, it is simple math to re calculate it. Over 10:1 will require high test gas and maybe retiming ign. Or correct it with a special gasket. Or go from flat top to dished pistons, or carve out thr combustion chamber.
Art Pearse

Hey folks, again thanks for all of the advice. The pistons are concave. Here is the latest wrinkle. I noticed that the # 1 push rod looked different from the rest. It seams that the pushrods are hollow with an "insert" in each end. On # 1 the lower insert was missing! I removed the exhaust manifold in order to remove the side cover and found the insert resting on the tappet. A magnet pulled it out. It appears that the insert is knurled to prevent this from happening. Would it be safe to use a little epoxy to hold it in place? I got the original pushrods with the engine and they are a solid shaft. Should I reuse one of the originals? Should I just buy another new one from Moss? In over my head, Tom
Tom in beautiful upstate NY

Tom,

I would not glue a push tube. I would get a new one that matches the others, a used one that matches the others, or a new set.

With respect to the pistons, at least two concave depths are available. I think they are something around 6 and 11 cc dishes.

Charley
C R Huff

This thread was discussed between 30/03/2009 and 06/04/2009

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