cylinder head, can it be saved?

[jeff jackson]

Hi All,
I have just taken my head to a engineering shop to be skimmed.
The chap there reckoned to get the water way corrosion away from the fire ring, (the cause of my water system pressurisation) would need about 5 thou taken off. I did think that this was rather a lot.
On checking the head we discover that is has been skimmed before and at best (more later) it has had about 7 thou taken off.
Reading the manual, only 10 thou is allowed to be taken off a T/C big valve head.
Also the chap says that whoever did the machining previously skimmed it like a "wedge of cheese" in his words. There is 5 thou difference from one side of the head to the other.
Around 10 years ago, I entrusted this head to QED who put hardened valve seats, new valves, springs and camshaft bearings. That little lot cost me 800 pounds. I have only covered around 12K miles since then.
What I'm wondering is this: QED must of machined the head after fitting the seats, because you can see the seat material in the surface of the head. (also the inlet valves sit proud of the head, is this normal?)
Which means they must of not machined the head correctly.
I am in a mess now.
What do I do with a head that is probably toast?
Is there any way, if I put a new head gasket on with shed loads of Wellseal around that waterway it will last?
Can I realistically machine the head flat and true, bearing in mind the amount of material that has to be removed?
If I told my missis how much a new head will cost she will have a fit.

Kind regards
Jeff 72+2

[rgh0]

You can shave lots more off the head than they say. The limit is really the water jacket under the exhaust port if you shave to much off you break into that and then have an expensive welding job to fix !

I have run heads successfully with none of the casting numbers left on the head face and that is a lot more skimming than you have had done

The seat material showing on the face of the head and the valve face edge sticking up above the head is normal in a shaved head especially with bigger valves and oversize seats fitted

I would weld up the waterway, reface the head and check all the rest of the dimensions to make sure its all OK with the head shaved to the degree it is and reassemble and all should be fine. You do however need someone who knows what they are doing to do the welding and check over the total head dimensions and adjust other things as needed to best suit.

cheers
Rohan

cheers
Rohan

[jeff jackson]

Hi Rohan,
Thanks for the encouragement. Boy! do I need some!
Even on a big valve head? At the moment the seat surface is marginal on the inlet. If we take another 10 thou off, these will be razor sharp. How much can we need to cut the valve seats back?
This then affects the compression ratio, valve timing and shims.....ARRRGHHHH!!!!

Kind regards
Jeff 72+2

[Quart Meg Miles]

Don't panic!

Taking 0.01" off the face will increase your compression ratio by 3?% so you'll be approaching 11:1 by now. I haven't noticed any difference after two or three skims. And it won't be the same on all cylinders as it has clearly warped a bit; don't blame QED for not cutting it level, it probably was when you got it but then you tightened it up and ran it a few times....

I assume you were jesting when talking about valve timing but if you are trying to sink your valve seats down a bit you shouldn't have trouble shimming it unless you are already down to .070", then you just grind the valve stems back a little.

[richardcox_lotus]

My cylinder head has been skimmed more than the book says. I'm now running vernier cam wheels to maintain timing.

All seems ok though !!

Regards
R

[rgh0]

Can you post a photo of the head face with a close up of the valve seats and valve position on the seat and the water passage that needs welding. It helps to see the actual thing to confirm the best repair approach. I would really need a bunch of detailed measurements to be able to recommend what is best to do around valves and seat positioning but I can at least give you general direction. But it is definitely repairable at a cost much cheaper than a new or second hand head.

You can see the valves sticking up above the face of the head in the attached picture

cheers
Rohan

[jeff jackson]

Hi Rohan,
I don't think I need the waterway welded. It will take a skim to get the the corroded bit out.
it's just scary because of what is written in the manual and Miles Wilkins book.
If I have already 7 thou taken out, with a 5 thou taper, that will be well over the limit to get it flat and right.
The seat is shown on the left circle, it seems to very close to the head surface, much close than what appears in your picture.
I know its not that clear, but the two circled bits on the right is where I believe I was getting pressure in the water system. the middle circle corrosion is up to and past the fire ring mark made by the head gasket. I had run the car up to hot, and removed the plugs, there was a small amount of steam coming from no.3 cylinder. Also spinning the car over with no plugs, water spots were shown on a card held over the top of no. 3.
I will try to take better photos, my wife has the good camera.
Again, thanks for any help, it's much appreciated.
Kind regards
Jeff

[rgh0]

The valve seat is not a problem. You may need to seat the valve a little lower if the skim cuts into the actual seating area on the valve seat but that should be OK.

What bore diameter head gasket fire ring are you using? The distance between the fire ring impression and the water holes seems closer than normal as the holes appear to not be centred between the 2 cylinders exactly and closer to the left cylinder in the photo.

cheers
Rohan

[billwill]

Valves poking below the level of the head is normal; thats why there are 'notches' in the pistons.

This link shows you how to do a clay test after your machining is done, to make sure that the valves don't hit the pistons.

lotus-twincam-f39/clay-test-checking-clearance-between-valves-pistons-t26441.html?hilit=clay%20test

Note, unlike wot I did you should not put full torque on the head bolts to do this test.
If the clearance is too little or zero, you can use a thicker head gasket or cut the valve deeper into the valve seats and as mentioned above, maybe shorten the valve stem a little.

One pic from the sequence in that topic.

[tonyabacus]

Hi Jeff
Where are you?
Like Rohan I think this can be saved but you definitely need to take some advice from a professional, if only to give you peacer of mind. John Wilcox is a guy who I have used in the past and seen him salvage heads that appear beyond saving, so it may be worth you giving them a call and get the head to him for inspection. They are based at Hinckley by the Triumph motorcycle factory. Take a look at his website, just had an article done on him in one of the mags which was very complimentary.

When you call don't be put off by Rita (John's wife) she is extremely knowledgeable and fields most call as John spends so much time in the workshop, but I don't think you will be wasting your time getting his opinion.
Tony

[jeff jackson]

Hi Tony,
I am in Poole Dorset. Thanks for your advice, and yes, perhaps I should take the head to a professional.
I was thinking about taking it to Miles Wilkins. He is only about a 2 hour drive from me. The worst bit about that would be listening to him moan on for 20 minutes about the cowboys who machined the head in the first place. (He would be right of course)
Hi Rohan,
The head gasket is exactly the same as the replacement bought from Susan Miller. I Can't find my vernier caliper at the moment to give you an exact measurement of the fire ring diameter. Also I will measure the height that the inlet valves stick above the head face. I think the caliper is at work so it would have to wait until tomorrow.

Thanks again for the advice.
Jeff72+2

[pharriso]

Hi Tony,

I was thinking about taking it to Miles Wilkins. He is only about a 2 hour drive from me. The worst bit about that would be listening to him moan on for 20 minutes about the cowboys who machined the head in the first place. (He would be right of course)

Thanks again for the advice.
Jeff72+2

Funny you should say that, I called Miles last Friday to ask about something & had a similar experience...