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Double Cylinder Head Gasket Horror !

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ianh

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Hi
Having just come thru' a range of horrors to get my 1954 BN1 back on the road I was replacing the cylinder head gasket.

On removing the head I found not one but two head gaskets sandwiched together.

Is this normal ? Should I replace with 2 new ones or try a single and see if the seal is ok.

It would be pretty tough to put it all back together only to find it was leaking badly.

I could splash out for a new composite gasket but they seem madly expensive (around ÂŁ200). Does anyone know a cheaper source ?

Any input greatly appreciated as usual

Kind Regards

Ian
 
I can think of a couple of reasons why someone may have used two gaskets.

1- The head or block surfaces are very warped or uneven.

2- The compression ratio may have been too high.

Using two gaskets would be unlikely to solve either problem reliably.

With regard to 2, if the head has not been milled, the distance from valve cover sealing surface to gasket surface on the cylinder head should measure around 3.670". Any less would mean a higher compression ratio. The standard pistons should come about .062" short of the top of the cylinder block, & have a noticeable dish in the center, around 24cc for standard pistons & 14cc to 20cc for the optional "M" pistons. Cylinder head combustion chamber volume should be about 62cc.

The head gasket should be about .060" thick. If any of these measurements have been altered, the compression ratio may be too high. The "M" pistons with .060" gasket would give a compression ratio of around 8.2 to 1. Standard pistons would be about 7.5 to 1.

If the head or block surfaces are uneven, more than .001" to .002", milling the minimum required to flatten them will be the only real solution. I wouldn't go much over 8.5 to 1 ratio for use with standard fuel, or 9 to 1 for higher octane fuel.

Compression ratio calculation requires that the below deck volume including piston dish, the head gasket volume, & the combustion chamber volume be known. This combined chamber volume, which is the actual combustion chamber volume, plus cylinder volume all divided by the combined chamber volume is the compression ratio.

It is anybody's guess what may have been done to the engine via machining, or what pistons may have been installed. There were/are many options available. You will just have to measure everything & see what you have.

The Hundred Four heads are notable for cracking, so don't go too far on this before having the head checked for cracks.

If by chance everything is ok but the compression ratio is just too high, there are special copper spacers available that can reliably lower the compression ratio when used with appropriate gaskets.

I would also suggest that you get new cylinder hold down studs, nuts, & hardened washers.

Sorry that I don't have an easier answer.
D
 
HI Ianh, one question.Why were you replacing the cylinder head gasket?.-Keoke
 
Hi
Having gently seeped for several years it blew
It may have been partialy disturbed when I put a new exhaust system on (straight thru 1 piece so lots of weight on side of engine) but this seems unlikely
Ian
 
No I do not think the exhaust systyem had any affect on it either Ianh.The four cylinder cars had inadequate number of head studs and were subject to leak. I would prolly use monkey engineering here { You Know monkey see monkey Do} /ubbthreads/images/graemlins/grin.gif. However, I was taking to a UK lister a while back he has had good luck coating the gasket with a non hardening sealer [Halomar] thinned with thinners and then allowing it dry before reassembly.Daves suggestion to replace the the studs nuts and washers is a good idea too. Those old studs just may be stretched a bit.---Fwiw--Keoke
 
I had a head gasket fail recently, the gasket supplier felt that the gasket had not been sufficiently torqued down, but supplied a replacement at no cost, anyway.
When refitting the head I replaced the head studs, nuts and washers. On close inspection,I found that the old washers were binding on the studs. I feel this may have led to an inaccurate reading at the tension wrench. I have recently completed a 3,000+ mile round trip from Brisbane to the Australian National Meet in the Barossa Valley in South Australia with no problems.
 
Well Pan, you can't argue with success so, Ianh : Bob's Your Uncle.---Keoke- /ubbthreads/images/graemlins/thumbsup.gif
 
Mine had the same, with a calculated comp ratio of about 12.5:1, kept blowing gaskets (2 off), when I rebuilt, had the head tested, first was the welding up of all the cracks (13), guy doing this heated up the head redhot and then using sticks of old crushed up metal from same age fixed them up, next step was putting the 0.125 thou back on the head face, this was done with a "spray on" material, so far some 3000 miles all is still ok, also took out the hi comp pistons and put in low comp pistons, also using a big bore gasket as the head chambers had been heavily modified, result is probably around 6.5:1 comp now, helps now that gasoline is now lower octane
 
Hi Guys,
Thanks for all your wise words.
I got the head measured & it was slightly over 3.67 inches
So I got a Welch steel gasket (ouch! that hurt the wallet) and new studs and washers/bolts.

Had great 50 mile run and leak seems to have stopped although now seems to pink/pre ignite. Had previously used 95 octane fuel so filled up with 98 and will wait to see if it stops once old fuel has run through.

It was a great run right up until the carbs float chambers started spewing fuel eveywhere and when I finally got to the bottom of that the battery warning light came on !!! Just to top off a great day, while pushing to the garage the screen cracked from a previous chip
anyone wanna buy a Healey ? just kidding (or should that be kidding just?)
Please see latest posting how to overhaul 100m carbs !!!
 
Ianh. Thats enought to leave one gutted.---Keoke- /ubbthreads/images/graemlins/laugh.gif- /ubbthreads/images/graemlins/patriot.gif
 
The carb problem may be as simple as cleaning the float valve needles & seats & correctly setting the float levels. At worst, replace the needles & seats & set the float levels. A good inline fuel filter at the carbs could go far to prevent future flooding problems.

Since you still don't know the piston dish volumes, the compression ratio may quite high. Be conservative with the ignition advance settings.

You could get a "rough" idea of the compression ratio with a compression gage check. Anything over 160 psi would be cause for caution.
D
 
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