Does my head need attention?

[Geoffers71]

My head looked as if it had been worked on at some point as the valves looked as if they had been newly ground in and everything was nicely clean and shiny. However on checking tappet clearances I find that 6 out of 8 are less than the allowable 60 thou, in fact the worst requires a shim of only 39 thou I think I know what some of the options are (shorter valves, thinner cam buckets, grind down shims etc) or go for the complete head refurb with new valve seats and valves. What advice, oh you of the greater knowledge and wisdom than I would be the best option NOT involving the last one. Is there any other option? Or, as I suspect, would I be foolish to do anything else BUT get new seats and valves. Just hadn't budgeted for major work that's all

[rgh0]

New valves and seats is clearly the best option but if your budget does not allow it the other ways you list are possible but need to be very carefully done to avoid other issues that can be even more disastrous to your budget. personally I would not recommend them and I would try to find the money to do the valves and seats properly

The biggest issue you face is that you need to ensure with whatever you do that the bottom face of the bucket does not contact the top face of the spring retainer. All the options make this a possibility especially with the valve with a the 39 thou shim need currently. I am not sure how you measured the need for a 39 thou shim but you need to make sure its a real thickness and not caused by the bucket hitting the top of the retainer during the measurement process

Thinner buckets are probably best next option - they will increase clearance and enable thicker shims but the thinner buckets have a thinnner bearing pad where they contact the shim so you need to check that the thicker shim brings the contact point up high enough so the bucket does not contact the retainer.

Grinding down valve stems - same problem of buckets then contacting the retainers not the shim and you dont want to get to close to the collet groove but say 5 thou off is doable if that helps the setup be achieved

Grinding down shims under 60 thou is not a good idea as even at 60 thou thick they can break ( I have one to prove it) and you also face the same problem of the bucket hitting the retainer but again its possible to go a little thinner by a few thou by grinding the shim if needed to achieve the setup. i have a couple of shims at 55 thou in my collection that I pulled from a engine being rebuilt If you do it grind them only on one side and put this side towards the bucket.

There are also different style valve spring retainers that provide more clearance to the bucket and accomodate thinner shims and the thin pad buckets better but these are really intended for racing applications and need new springs and the setup height may be an issue as they are intended for high lift racing application


Good luck with whatever options you choose but I do recommend you try to find the money for a new valve and seat job
cheers
Rohan

[john.p.clegg]

Win/Win situation here...There is also the option of getting the cams reground to a pokier spec. (which means higher lift/smaller base circle)

John

[Elanintheforest]

What a shame Geoff....the head did look good! I wonder if my early head would be any better

I had new seats and guides, and new valves, popped into an engine a few years ago, and given the stage you're at, it's not a big job. Total cost was under ?500, and that included upping the valves to Sprint spec and a bit of port polishing.

A set of valves now is under ?200, so I doubt that the price has increased by much since then.

It sounds like a lot of work to try and 'make do' with what you have, but I doubt very much if you would be happy with it, every time that tachometer went over 4000 rpm!

Mark

[Geoffers71]

Hi Mark, Are you saying you would still be up for swapping heads?
No saying the other head doesn't still need similar work of course, but if you want to,,,,,,,,,

[Elanintheforest]

I'm happy to swap them Geoff, but of course it would need the same work, and probably more. It was fitted in 1972 to convert the car from Strombergs to Webers. The car ran for another 60,000 miles without further work, and was taken off the road in 1984, 30 years ago.

So it would certainly need valves, seats and guide, and maybe a bit of work to the water channels and face.

But it's a complete unknown currently....how lucky do you feel?!

Mark

[Geoffers71]

Mark, you have a pm

[Geoffers71]

Bit the bullet and dropped my head into my friendly local engine restorer today. On first superficial observation he confirmed my first thoughts about the seats, but he will only give a final verdict when he takes it all apart and measures it up for himself. He does speak with apparent authority about the twincam and has worked on a fair few, so that's reassuring For example he said he needed to check if any valve tips had been ground or if the buckets were standard. He noticed too that 2 cam buckets were marked and would need replacing and one cam stud needs a helicoil and new stud, which I knew about and had already bought a replacement. There was also some evidence of welding near the camshaft front groove which I hadn't noticed. Initial estimate IF it doesn't need 8 new valves is ?500 + VAT. Anybody want to buy a kidney?..... well used and of doubtful quality but hey if you're desperate.