Valve to guide clearance

[type26owner]

It's entirely possible to weld on enough material to build the head thickness back to stock. I've seen this done this on several occasions to racing engines. The downside is the camshaft bores will have to be line bored true again. I have a well made line boring tool to do just that I inherited from a friend that had a small repair business at one time salvaging blowed up engines. The only downside is you need the services of a true welding artist.

[M100]

I've a spare head I'd like to get up to scratch for my Sprint and its been abused in the past with overtightening but other than that its in quite good condition (a small valve head with plenty of head thickness, no cracks and minimal waterway corrosion)

What's the view on approaching the situation where the head washers have indented the head?

Is spot facing the only way to go?

[type26owner]

IIRC, Rohan and I discussed this situation before and never came to any clear cut conclusion. What should be done minimally is the metal that's plastically flowed into the clearance holes should be reamed out of there. You must use dowel pins to align the head gasket correctly and there are only two clearance holes the right size in the gasket to allow that to happen. The front hole on the exhaust side and it's diagonal farthest opposite one. Not using the dowels virtually guarantees a blown head gasket soon there after particularly if it's a racing engine. Using the old style aluminum and copper faced head gasket is risky at best. There is a much better composite head gasket available now that is almost foolproof for the really high compression engines.

A new set of ARP head bolts would be wise too. Did the check that ARP tells you to do on the block for adequate thread depth and found one was short on mine. Had to drill the hole another 1/8" deeper and bottom tap the thread so be aware it could happen to you too.

[M100]

The holes are ok and full clearance size but its just the top face thats a bit mangled, maybe compressed by around 20 thou and in some places grooved under where the head washer fits.

Are you suggesting machining dowel holes both in the head and the block to ensure gasket location? All I've done in the past (purely for road use on a standard tune Sprint engine) is use the relatively tight fit of the dummy head bolts to hold the gasket in place until the clamping load is on - (then relying on the gasket digging into the soft head to stay put!)

I'm aware of the ARP bolts but wondered if there an easy way to use head studs instead - its always seemed a strange compromise on a performance engine

[type26owner]

20 thou is no big deal. Go ahead and assemble it. I've seen a lot more metal moved then that. I have one boss which is developing radial cracks on my Elan.

Look in the Lotus manual and it shows the removable dowels pins in an illustration in the engine section. Once a couple of head bolts are snugged up the dowels are removed to permit the headbolts to go in those holes. Don't know if the dowels are sold by any parts vendor or not.

Because of the huge difference in the coefficient of expansion between the aluminum head and the cast iron block the headbolts must stretch and store enough clamping energy to accomodate the movement. Do not mess around with any studs. The ARP bolts are tailor made for this application. The head expands by about 1mm more then the block in the long direction when the engine gets up to temperature. It's really a miracle the head gasket can seal this situation up at all. That's why the surface finishes of the head and block must be held to very close tolerances.

[rgh0]

I agree with Keith that 20 tou depression in the head top from the bolts should not be a problem as many heads show this sort of imprint after 30 years.

If it gets a lot worse than the current 20 thou the right repair IMHO is to countersink a hardened steel bush into the head for the head bolts to bear on. The stresses of this boring and then pressing the bush and the relieving of the existing stresses in the head caused by the metal flow may require line boring of the cams if the metal flow has not already affected cam alignment.

The only thing worth checking if your concerned about the heads condition is whether the head aluminium has gone soft through age and overheating. If this is the case then the bolts can continue to sink rapidly into the head each time they are tightened and you loose bolt tension and have continually blowing head gaskets no matter how careful you are with surface finishes and initial bolt tension. its always worth measuring the depth of these depressions before assembly to ensure they have not got deeper the next time you have the head bolts out.

Rohan

[GrUmPyBoDgEr]

I know of someone who tried to salvage an FVA head that was damaged where the cylinder head bolts sit as previously described in this thread. He got the areas built up by welding and the re-spot faced the bolt seating area.
When assembling the engine he was unable to achieve the necessary torque values. The welding had softened all of the material and it just flowed away during the bolt tightening.
An expensive mistake!

[type26owner]

I'd use Ampco 18 aluminum bronze inserts amd glue them into a loose fitting counterbored pocket. The trick is spread the load enough so no plastic deformation takes place in the low modulus aluminum. The AB is my best choice because it resists cold welding even under extreme loading. The grain structure is such that when it fails it does not tend to roll a ball of material along galling the surfaces. Instead it breaks up into a powder. The hardened washer on the bolt stays of course. Going to have give it a try next time around rebuilding my head where the boss is cracking. I may already have a problem because of this since appears I have a small quanity of mystery coolant disappearing now on a regular basis.

When installing the head it's best to cool it as much as possible but not so much it forms condensation.

[Matt7c]

Wow, this has developed into a really interesting thread! Taking the conversation back a few day, having thought it through some more, I've decided on the machine shop option. I don't currently have the tools to do the job myself and also time has now become a factor. Think I'll use Price Brothers Auto Engineering in Bristol who say they are a family firm with 25 yrs experience and have done lots of Lotus TwinCams over the years - anyone out there have experience with these guys?

[SJ Lambert]

20 thou is no big deal. Go ahead and assemble it. I've seen a lot more metal moved then that. I have one boss which is developing radial cracks on my Elan.

Look in the Lotus manual and it shows the removable dowels pins in an illustration in the engine section. Once a couple of head bolts are snugged up the dowels are removed to permit the headbolts to go in those holes. Don't know if the dowels are sold by any parts vendor or not.

Because of the huge difference in the coefficient of expansion between the aluminum head and the cast iron block the headbolts must stretch and store enough clamping energy to accomodate the movement. Do not mess around with any studs. The ARP bolts are tailor made for this application. The head expands by about 1mm more then the block in the long direction when the engine gets up to temperature. It's really a miracle the head gasket can seal this situation up at all. That's why the surface finishes of the head and block must be held to very close tolerances.

G'day Keith

I'm not sure how long ARP head studs have been available, but for a head that one feels might be susceptible to the beginnings of compression do you think that the studs would offer any advantage over their bolts?

Is there any easy (or even not so easy) way of testing whether any cylinder head has begun to soften? I have a standard one that I've just removed from a complete, but long idle engine, the whole engine is in fairly reasonable knick, but has seemingly done a fair bit of work - bores still at 83mm and head gasket wasn't blown. Standard crank has had all the life ground out of it and I don't know the "history" of the engine, so biggest complaint is that there is a bit of cylinder head bolt compression...........

Cheers James

[rgh0]

Hi James

Orgers can do a hardness test for you and we can discuss what the results mean. They routinely do a check on all twin cam heads to avoid complaints from owners with soft heads of blowing head gaskets after they have worked on them, they are somewhat conservative in what hardness they consider acceptable to avoid later claims I think.

A visual check looking for extensive head bolt recession ( a small amount is normal, say less than 1 mm, greater is an indication of maybe a soft head) or indentation in the head face from the fire rings will tell you if the head is maybe soft and a hardness check is needed.

regards
Rohan