The Triumph Dolomite Club - Discussion Forum

More woes I'm afraid. Took the head to the local specialist to get the head checked to ensure it was flat and the report back was literally "your head is as soft as a slab of butter in the midday sun". When he pointed out the grooves in the head from the metal edges of the Payen gasket, I could see what he meant. Couple that with the fact that about 2mm has already been machined off the surface over time and it looks very much like cylinder head RIP. Problem is that I had acquired it many years ago as a 'ported and polished' head with STR139 cam.

I have two spare heads, both reportedly 'standard' and both seem to have lost about 40 thou off the face. I now have to get these tested, pick one and then decide on how to modify and to what spec. I have compared both of these to the Leyland ' Specification for International Group 1 Race/Rally' papers I have and they seem to meet that exactly. Mistakenly it seems I had thought the Group 1 specs to be modifications. The 'soft as butter' head is still at the workshop so unfortunately I can't measure that at this moment.

I am mating this to twin 45 Dellortos on a manifold that has a 45mm wide opening to mate to the head, which is in fact smaller than the 48mm inlet opening on both spare heads. I am also using the standard Sprint exhaust manifold. Given the limitations imposed by in and out gas flow, what, if anything should I do to the chosen replacement head? (Currently it will rev easily to 7-7500 and appears to want to go higher, which I can't do with just a standard bottom end). Given this type of work is well beyond my capabilities, I am going to be paying commercial rates for any work done so, while I don't want to spend more than I need to, neither do I want to end up with a car that is slower than in it's current spec. Ideally I would like it to go faster still!

Appreciate any thoughts and advise.

Geoff

The only thing to have the same specs is to copy the old head. I would not skim the "new" head 2mm. If anything happens with it it's a rip too. You can skim 1mm to have a more compressio and skim the engine deck to have the rest. You have to measure the combustion chamber and then calculate what the original compressio was. After skimming the new head 1mm measure that too and you know how much the deck has to be skimmed to have the old ratio. This way you can use your new head longer. To have the deck skimmed is less expensive than another head porting again and agian. Copy porting a new head with the right tools is not that much work because you can copy and don't have to experiment. It's alloy so easy porting with a alloy grind.

Jeroen

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Just took the two spare heads to the specialist and while they are marginally harder, he says neither is good enough. This is all new to me but his comments were:
He would expect a good head to measure around 120 on the equipment he uses and he wouldn't recommend using anything that measured below 70. Both spare heads did register about the 120 around the casing surface in front of the cam chain. By comparison, the old race head was down in the low 30s between the bores and only in high 30s next to the bores on the sides. Both spare heads measured in the 50s in these areas, with one dipping into the 40s and the other up into the low 60s. The better of the two was off an engine I know had done about 185,000km and the other is one I bought as is.

Plan is to keep the better one as a spare and try to reharden the other one. Apparently that is not a guaranteed process, but hopefully will work. That will mean stripping all steel off the head, including seats and guides which will be done tonight and Saturday morning. He agrees with you Jeroen that the porting is a minor issue by comparison. We all agreed that the current head is best scrapped as it would require a further skim and that would just about remove the two fixing holes on the casting in front of the camchain aperture! The one we are going to try hardening has been skimmed 1mm already so that will be okay with just a light skim hopefully.

Will let you know how I get on.

Geoff

Hi Geoff,

Sorry to hear of your problems, but I am sorry but I don't agree with your engine reconditioner. I have heard of this problem so often, ie "my cylinder was head tested and it is too soft". My answer is so what. You must remember that these are are very old technology alloy heads. In the early 1970's how many cars were using alloy heads? I am no casting expert but my guess is that Sprint heads were sand cast, or gravity cast and modern heads are more than likely pressure die cast.

The chap who does my engine machining is now 70+ years of age and been doing machining for over 50 years. When I spoke to him a about this so called "problem" his answer was so what is the problem? He never tests the head for hardness. Does not feel it necessary. As long as the head is not distorted and does not leak, just use it. The impressions in the head face from the head gasket, between cylinders, is normal if you are pulling the head down ad bit more than normal torque. 2mm of the head face is a lot, but I have used thinner, but personally I would not scrap the head. If you don't want to use it send it my way, because I will.

It is your decision, but I personally would not spend money on having the head heat treated, is it the correct material to be heat treated? More than likely if it is heat treated the valve seats and guides may need to be replaced. Now that is VERY expensive. I would leak check head, skim and refit and I would bet your money that is will be OK or no different to spending a lot of money having a head heat treated.

Good luck

Mark

Haven't you thought of having the head face re welded and then skimmed
I have seen a lot of heads at my machine shop that are done this way
I know of a Cosworth engine that had his re welded as it had been skimmed
To death
700 hp and no problems at all
May be worth considering !

On another note
The gasket biting into the soft alum may help you with
Head gasket sealing just have to check the head bolts a little more often

I concur......
Loads of Heads are binned without people looking into other options of saving them.

I agree. My cylinder head is "o ringed" to improve sealing. When I pulled a motor apart I found a head gasket that had failed but the leak was stopped by the wire ring that was set into the head face.

I really don't think that a soft head is a problem, because I believe that all Sprint and probably 8 valve heads were made that way, and maybe Stag. It would be interesting to have all tested. As I mentioned earlier I am sure that they are softer than any of the modern day cylinder heads. I would be talking to a someone who knows more about modern casting process before believing an engine reconditioner.

Mark

i too had my engine wire ringed but it was done on the cyl block

I think they call it Wills rings and was standard practice on Hillman imp engines when tuning them.

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The lunatic is out................heres Jonny!

Geoff

My tuppence worth – for what it is worth.

I spent ten or more years heat treating high speed steels, making precision hand tools and all that tells me is that my metallurgy knowledge is extremely limited! However I think Mark is offering comment that if it was me I would accept. Yes the casting of metals is an art which is changing all the time but I would be inclined to seek another opinion before either abandoning your ported head and certainly before sending it off to Mark to use.

It is as “soft as a slab of butter in the midday sun” and there is some variation in hardness across the head itself.

What is the hardness figure that you have been quoted? Relative to what scale of hardness? (There are several scales). Is it still within the manufacturer’s tolerances? (I would be surprised if someone can provide us with that information).

Mark’s statement that if the head is not distorted and does not leak, just use it, seems a pretty fair option to consider. If it does leak sometime later, then decide later what to do.

You have had your other heads checked, for hardness but until we know what hardness scale the local specialist is using I am not sure that it is telling us a great deal. My specialist checked my head for hardness against a couple of Stag heads and based on his 40 plus years of experience said it was what he would expect. No problems at all.

I have fitted Wills rings to my block – rather than my head, and I would expect to see some marking on my head in due course simply because there will be much higher point loadings above the rings – which is why they have been fitted, to provide better sealing.

Unfortunately my local expert at Impwerks, he had a business tuning Imp engines and sending them all over the world, is on an extended sabbatical so I cannot ask for his comment but I feel pretty sure he would concur with Mark.

I can only summarise by saying that metallurgy is a bit of a black art, there are so many variables. And that if it aint broke then don’t change anything.

You want to go faster still? Fifteen years ago I would have suggested buying a ticket on the Concorde. The ultimate way to experience speed for us mere mortals.

Three out of three too soft ? That would seem to be how they are meant to be as per Mark's comments. This was the norm in the 70's it would seem.

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Mike

1980 Vermillion Sprint - 174bhp

Being new to the SPRINT saga of alu heads and the over skimming issues, which no doubt have in the past been chewed over on a number of occasions..

I was informed by my local 'old n very experienced non bullshitting engine man' when I asked him about sprints n heads when i was thinking about buying another that overskimming wasnt a problem as 'metal' gaskets to make up the amount of metal removed are available! I'll inquire over the softness issue too if this would clear it up as this chap will know, and will give his honest opinion

Sorry to revive an old thread, but just wanted to add a little of my experiences.
For the new Sprint engine I am currently building I had two old Sprint heads checked last year.
And the verdict (by an old school engine builder specialising in Ford) was that,
compared to the alloy heads he usually works on, the castings and quality of the alloy weren't bad at all.

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