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[Ivor]

My 2003 500 ES has blown it`s head gasket for the 2nd time in 1000 miles. I torqued it down after approx. 150 miles 2nd time(forgot 1st time so my fault)I don`t ride it hard so I`m wondering if I should torque the head down more often?
Maybe it would help to have the head skimmed and use a copper gasket instead of the composite ones.
Any thoughts?

[Tim NZ]

It is possible the head has already been skimmed? And THAT is the cause of the blowing?


The Spigot height on the barrel is not sitting into the recess in the head correctly.


Check height of the spigot V's the depth of the recess in the head. You need at least 0.005" crush onto the gasket. AND the same depth & height all around.


I prefer the composite gaskets to the solid copper as they are more compliant to surface irregularities.


In extreme cases it is not unheard of to run two head gaskets as a stop-gap fix-me-up.

[Tim NZ]

(Half my reply vanished?)


Excess carbon build up in the rebate in the head will prevent the head crushing down onto the gasket...


DONT over tighten the head nuts! It will lead to stripped threads and a distorted bore! I frequently encounter barrels where the nut between the pushrods has been way over-tightened in a forlorn attempt to cure oil leakage. Over-tightening that particular stud distorts the barrel and leads to ring blow-by and bore washing if running too rich.

[Alan R]

Hi Guys------TIM, I had the same trouble this morning------Have a look at the different font style for my reply in the heading "CGT535".... It's like that because I phoned our hosts to inform them of the problem and then E-Mailed the whole thing in, and it was thus entered that way..........Re}-- barrel/head "crush"...Personally I tend to go for ten thou ( 0.010" ) and the thinnest copper gasket available properly annealed and cleaned, with a thin ring of gasket sealant around the various holes to prevent oil seepage..To the "Non-Engineers" of you out there if you have an older 6"ruler marked with 1/100's of an inch ( ie 0.010" or Ten thou. ) you'll notice that the gap between each black etched line is almost the same as the thickness of those lines...In other words you can actually see what ten thou looks like.....And yes, both faces flat AND square to the bore axis is just as important..

IVOR, you might want to consider our hosts hardened washers in place of the OE soft ones....

[Ivor]

Thanks for the advice. I have got the hardened washers already installed. When I first took the head off It was a hell of a job and I had to resort to the "Indian rope trick" to force it off.
It is coming apart soon so will check the clearance between barrel spigot and head. I suppose if the clearance is too small then you can`t just machine down the barrel spigot as it will alter the compression ratio.

[simon]

Hardly at all. I had to machine the firelip on my B44 recently. Id had the head rebuilt for a specific barrel that then had its liner slip and when I replaced it with a new NOS barrel the firelip was higher and as a consequence there wasnt sufficient crush on the gasket. Turned off .004" off the lip and the barrel as it was cheaper and far easier than machining the head and problem solved

[Bullet Whisperer]

Skimming the head and / or the liner spigot won't make any great difference to the C.R, - when I tune these engines, I usually remove about 2mm from the barrel height in order to get a worthwhile increase in compression for fast road engines, usually with a higher compression piston fitted as well.

[Ivor]

Interesting comments. Thanks to you all. Will get stuck in next month and see what I find. It was burning a bit of oil as well as leaking so it needs a good seeing to...!