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+--- Thread: Replacing cylinderhead (/showthread.php?tid=3556)
RE: Replacing cylinderhead - Steve Bryant - 10-12-2019
At our shop we have had a number of head gasket related issues with Austin Healeys , MG Bs, Minis and other classic British cars which seem to be related to the type of head gaskets that are currently being sold as the replacements for the original OEM type. Some are better than others at sealing but those that don't have caused no end of issues with sealing. All of the engines in question were rebuilt with both the heads and cylinder top faces having been machined flat, new studs and nuts installed and the torquing of all the nuts done to spec.
What did work for us was a spray on gasket sealer designed for this type of application. A light coat applied on both surfaces as per directions and everything assembled with all mating surfaces absolutely clean and dry.
A talk with your knowledgeable motor factor supplier should be able to advise you on the best product available in your country for this application.
Stephen
RE: Replacing cylinderhead - "Slack Alice" Simon - 10-12-2019
How do you apply the silicon?
If I use the nozzle I cannot control the output very well.
If I spread it, it isn't very even.
And, if left to cure, doesn't that make the uneven-ness permanent?
Details please, Mr. Wizard!
RE: Replacing cylinderhead - JonE - 10-12-2019
I'm glad you posted that, Simon! - I was thinking I wasn't sufficiently learned to comment, but Steve's comment really brought it home to me that a directed aerosol spray would be the ideal thing. I wish I had photographed the gasket I did have to remove with Loctite silicone on, to observe the pattern of what occurred from finger spreading. (No problems with the joint, just removed the head for other reasons)
I'm presuming Ruairidh meant that 'leaving to cure' is not starting up the engine till the next day.
How long do others feel that the working time for the 'spreading' stage is?
RE: Replacing cylinderhead - Ruairidh Dunford - 10-12-2019
Simon,
I have just spoken to Jon and I will now give you a buzz too.
RE: Replacing cylinderhead - John Mason - 10-12-2019
I have read this thread with interest. Could it be possible that the problems with head Gaskets not sealing and allowing water seepage into the bores could be caused by how the head is replaced. I have been involved with seven for the last 20 years and in that time done 6 head replacements and only one case caused leakage problems (that being caused by uneven mating surfaces). I only use a smear of GP grease to both side of the gasket then tighten down in the sequence shown in Woodrow. I never use a torque wrench just a normal length spanner to hand tight. I then run the engine up to hot and again tighten again in sequence to hand tight whilst still hot. I think when hot the studs expand greater than the head thus allowing space to tighten again sealing all water, oil and gas passages between block and head. This is so what different to a lot of mechanics who let the head cool again before re tightening. This is of course only with cast iron heads. Ally heads only to be rightened cold.
John Mason
RE: Replacing cylinderhead - Paul Nott - 10-12-2019
Didn't realise what I'd unleash when I started this thread, great thing about this forum is you never know where it will lead, many opinions all given to the benifit of all.
Anyway the head is on, finger spread a light covering of Loctite 5920, tighten head and finally started her up two days later.
Only reason I waited so long is that once fitted the original plug leads were to short and a carburettor fuel leak need rectification.
Dare I ask should i retighten after a few miles?
A little bit more fetilling and we should be ready for next years Measham rally.
RE: Replacing cylinderhead - Renaud - 10-12-2019
Hello Paul,
I don't know if it will leak (hope not!) but hell, how great this all looks!
RE: Replacing cylinderhead - JonE - 11-12-2019
Paul - as per John's post above. Remember xmas lore
if iron head you got -
re-tighten hot
aluminium? less bold!
re-tighten cold
RE: Replacing cylinderhead - John Mason - 11-12-2019
Jon E I like the rhyme to aid remembering which head is which.
John Mason
RE: Replacing cylinderhead - Paul Nott - 11-12-2019
Well it's not gone quite to plan today.
Added fresh anti freeze and ran up to temperature, only to find water running from header tank on to fan assembly.
Investigations found a poor previous repair with a large amount of putty covering damaged area.
It looks like the area where the filler kneck joins the header is cracked.
In your experience is this a simple repair or a job for a specialist.