Classic cars forum & vehicle restoration.

[1935Hillman]

Owing to a blown head gasket I have just had the ally cylinder head (sidevalve flat head) skimmed prior to refitting. Unfortunately we have noticed slight marks in the head created by the valves striking. This leads us to believe that the head has been skimmed too many times in the past. Does anyone have any prior experience of such a situation and is there any way of resurrecting the head? I did think about double gaskets but I can see that this may cause slippage of the head and resultant leaking.
Any ideas at all?
Many thanks,
Tim

[PAUL BEAUMONT]

I guess an indepth investigation is needed to establish if all valves strike and by how much. Do they hit the head square on of is it just a crescent?
Could you locally machine the head to give relief? could you slightly shorten the valve stems to generate clearance without reducing performance?
I guess the real question here is: If the head has been skimmed many times, what is the overriding problem. It sounds a bit as though at some point in the future you will be doing the job again!

Not a lot of help, but no one else seems to have commented!

Paul

[1935Hillman]

Hi Paul,
Thanks for your post. The reason for several skims is simply a 75 year old ally head. Its seen a lot of decokes in its time and probably has a had a trim up each time to straighten it.
I think I may go for the local relieving option. I could get the head bored out a little just to make sure they don't strike and be happy with that.
I'll let everyone know how it turns out

[Rick]

Is it not worth investigating a second gasket, or perhaps having one made to slightly thicker dimensions? I'd be wary of machining into the combustion chamber in the head, for fear of striking a water passage behind (if there is one nearby).

RJ
_________________
Rick - Admin
Home:https://www.oldclassiccar.co.uk
Videos:https://www.youtube.com/user/oldclassiccarRJ/videos
OCC & classic car merchandise (Austin, Ford ++):
https://www.redbubble.com/people/OldClassicCar/shop

[Jim.Walker]

Many old motorcycles use annealed solid copper gaskets. It might be worth experimenting along those lines, cutting a gasket from copper sheet of suitable thickness?
Jim
_________________
Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then!

[1935Hillman]

Thanks all,

Yes, I have had a serious rethink since yesterday and am going to get a thick gasket laser cut by a local firm. They seem to think I can have something cut out for about £100 including the copper which will solve the problem in one fell swoop. Got to be worth a go I think. The difficulty is in not having a new head from which to take measurements. I can only guess at the original valve clearance and keep it tight to maintain compression. It was marketed as a 'high compression' engine in 1935.

I will report back

[Handyman]

£100 for a copper head gasket? That do seem like a lot of money. I make up solid copper gaskets for racing bikes and they come nowhere near that price.

I would suggest measuring the volume of the combustion chamber to see what the current volume is and compare that to what it should be as standard. It would then be possible to calculate the thickness of gasket required to achieve the original volume.

It is quite easy to measure the valve to chamber clearances, to see if the head can be relieved. Stick a bit of plasticene on the valves, bolt down the head and turn it over by hand once. Lift head and see how the plasticene has flattened or distorted. Its then possible to check all the valves to see if the clearances are the same. BTW, shortening the stems is not the answer.

If the head is beyond redemption, contact me as I can probably sandcast you a replica in LM24 or something similar, that wont distort. 1930s alloy tends to be merde as they still had not sorted out the metallurgy and remove many of the impurities. WW2 and the requirement for better materials brought on metallurgy leaps and bounds.

H