Lotus Elan

Twincam head machining issues?

PostPost by: Jaylow » Sat Sep 19, 2020 6:11 pm

Just got my head back from the machine shop from having new valve guides and the exhaust cam follower sleeves replaced, and would be grateful for some advice from wiser heads about some aspects of the work done before I go back to the machine shop with some questions,

Firstly, the head appears to have been refaced; it is clean and shiny, (a lot more so that when I gave it to the machine shop) and appears to have some machining marks. I didn't ask for the head to be skimmed, and the invoice didn't include a charge for it. I'm concerned that the machine shop may have warped the head during their work and skimmed to correct. The tops of the raised lettering on the underside of the head have just begun to be skimmed as well. Should I be concerned?

Secondly, the old cam follower sleeves were returned to me intact. I was expecting them to have been cut or machined to remove the tension before being extracted (and hence my concern about cooking the head to extract them). Is it possible to extract the sleeves without relieving the tension or cooking the head?

Thirdly, the cam followers rock in the new sleeves; almost as much as the old exhaust sleeves, and noticeably more than the inlet sleeves (which were not replaced). Is this usual, and is it likely that the new sleeves have been over machined?

Fourthly, the new valves stick slightly in the closed position, which I understand is generally a sign that the valve seats need to be refaced. This has supposedly been done (and invoiced for). Will it go once the guides have been lubricated and with a bit of lapping, or is this something that needs to be fixed by the machine shop.

I was planning to ask the machine shop if they have skimmed the head, and why, and to what tolerances they had machined the cam follower sleeves to. Is there anything else I should ask?

I'm also thinking of getting a second opinion on the clearance of the exhaust cam follower sleeves, and wondered if there was somewhere in the South Oxfordshire / Berkshire / Buckinghamshire region that could be recommended?

Any advice would be gratefully received.
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PostPost by: 69S4 » Sun Sep 20, 2020 10:14 am

I'm not qualified to comment on whether the work you've had done is up to scratch or not but I'm sure others who know these engines better than me will be able to. Hopefully they'll be along shortly. I'm also in the South Oxon area - Thame - so now I'm wondering who you used. :) The last time I had work done on both the head and block I used FJ Payne in Eynsham. They did a perfectly satisfactory job and the engine's been running well for the last 10yrs or so.
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PostPost by: Foxie » Sun Sep 20, 2020 10:41 am

It is normal for machine shops to do what they call a "service skim" on all heads they get for work, as every head can develop a minimal warp after being in service. They remove the very minimum to give a level surface, as opposed to removing a calculated thickness of metal to increase compression ratio.

Valves sticking to to seats are a good sign, indicating that they are well lapped.

I would, however, get the cam buckets checked. Also see here:
viewtopic.php?f=15&t=19293&start=

:)
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PostPost by: 512BB » Sun Sep 20, 2020 10:46 am

Good morning Jaylow,

Not sure if that is your name or if you are just a fan of the woman with the fat arse? Perhaps you could enlighten us.

Anyway, welcome to the forum. Its a shame your first post is with what I see as quite a few problems. You did not want to come here to ask for references first, before entrusting your valuable head to someone?

You wrote 'Firstly, the head appears to have been refaced; it is clean and shiny, (a lot more so that when I gave it to the machine shop) and appears to have some machining marks. I didn't ask for the head to be skimmed, and the invoice didn't include a charge for it. I'm concerned that the machine shop may have warped the head during their work and skimmed to correct. The tops of the raised lettering on the underside of the head have just begun to be skimmed as well. Should I be concerned?

I think it is unlikely that they warped the head. Unless you took measurements of the head before you gave it to them, you will never know how much they skimmed off it, something I always do before leaving my heads with anyone, including taking good pictures. They may have skimmed just to clean or true it up, you will have to ask them.

You wrote 'Secondly, the old cam follower sleeves were returned to me intact. I was expecting them to have been cut or machined to remove the tension before being extracted (and hence my concern about cooking the head to extract them). Is it possible to extract the sleeves without relieving the tension or cooking the head?

I do not know the definitive answer to this question, and different companies will have different methods of removing follower sleeves, but I would have thought that heating the head to a certain correct temperature, whatever that might be, was the way to go. And the same for replacement of new sleeves. Obviously the head should not be overheated, or the head may go soft.

You wrote 'Thirdly, the cam followers rock in the new sleeves; almost as much as the old exhaust sleeves, and noticeably more than the inlet sleeves (which were not replaced). Is this usual, and is it likely that the new sleeves have been over machined?

Eer, no, this is NOT usual. Your new buckets, you should have new buckets if you have new sleeves, should ALMOST be an interference fit in the new sleeve. Some years ago, a mate of mine had his head overhauled by George Robinson of Twincam Techniques and this was how the new followers fitted in the new sleeves. The tollerances were amazing and runs like the proverbial sewing machine.

If I was you, I would not ask the company who carried out the work anything for now. I would find another firm who come recommended. Just a short while ago, someone asked for a recommendation in the same area you are seeking. Search the WANTED ads or the ENGINE forum and you may find it, or someone will be along shortly to help you. Take the head to them and explain the situation. Ask them for a report in writing. You may have to pay them for their time. Never divulge the company who carried out the original work, to anyone, FOR NOW. I made that mistake years ago.

Then act on the report and write to the company who carried out the work, enclosing a copy of the report. As a matter of fact, you DO NOT have to give the original company the opportunity to correct their work, if you have lost confidence in their ability to carry out the work to a good standard.

Look forward to reading other peoples views. Best of luck.

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PostPost by: nmauduit » Sun Sep 20, 2020 10:51 am

just my 2c

1) are you 100% that the head has indeed been machined and not just tank cleaned (e.g. via head thickness measurement)? if only very lightly skinned (say 10-15 thou or less) that would not be a concern, though doing it without telling about it (before, or at least after) would be in my book (ps. had the head been surfaced a lot prio to this time? the cast lettering are quite low so that means total thickness is likely well below 4.6" now - were chambers volume balanced prior to this intervention?)

2) the sleeves possibly could have been liquid nitrogen shrunk to help taking them out : again, a word from the machine shop when picking up the part or on the phone would be good practice (in the line of we've found this, done that, recommend this or that etc)

3) I would be wary about this the most of your list, and would try to document actual play quantitatively (bore vs. bucket size at various heights and in various angles) - again a word of the machinist may help clear up the issue...

4) are you using new valves ? this may not be a main concern (depending on the amount and actual cause of stickiness) - also, iI undestand many modern machine shops cut seats in a way the should not (or minimally) be lapped for best seal (you may check actual ring seal thickness, location and appearance with some machinist blue or equivalent)

in doubt, a second opinion would help to regain peace of mind before reassembly (if need be after additionnal or corrective work)
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PostPost by: steveh » Sun Sep 20, 2020 11:16 am

Hi Jaylow,

I think most of us have been there having spend good money on machining and parts to end up with a shoddy job,sometimes with a bit of dishonesty thrown in.
I concur with Leslie's comments .
Issue 4 -- the seats have not been cut concentrically to the guide and lapping is not the solution, they need cutting.
Get some engineers blue on the valves to check the contact with the seat ,it will show whats occurring.
Their same standard of workmanship is what you will receive if you go back , i would'nt go back ! .

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PostPost by: 2cams70 » Sun Sep 20, 2020 2:39 pm

It's important that the guide to valve stem clearance is correct. If the valves are sticking they could be too tight.
I once had the experience on a crossflow engine where the guides had been machined with not enough clearance.
The engine started and ran fine until I started to drive around 500m down the road. First there was a light tap, then a louder tap, then a bang bang! Stopped the car at that point and walked home. Pulling the head off later revealed that one of the exhaust valves had started to stick in it's guide due to stem expansion from normal engine heat. The valve had been bouncing off a piston. Luckily no serious engine damage occurred. It could have proved fatal.
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PostPost by: wobblyweb » Sun Sep 20, 2020 3:10 pm

Just had my head done by Exon Engineering and very happy. He pointed out a broken guide, replaced them and found a cracked seat. Skimmed the head after and supplied photos to show the work and problems.
One guide was oversized O/D but he said they sometimes came from Lotus like this?
The head was severely warped the result of overheating.
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PostPost by: mark030358 » Sun Sep 20, 2020 4:09 pm

Who did it first of all...
Some posts on here reference people not to use. I have used QED (before they stopped machine work) then Paul Exon, who did a good job for me, but others have different opinions.

regards
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PostPost by: alanr » Sun Sep 20, 2020 4:37 pm

Sorry to hear about your cylinder head concerns following work being done.
After a bit of research I used Knight Engine Services, aka Cylinder Head Services, Nether Heyford, Northants. earlier this year for valve guides, valve seat replacements and light skim (4thou skim and no machine marks whatsoever!).
I was very pleased with the work they did to my head and they did exactly what I asked for even though they were a little bit slow in doing it. David Knight (owner) is a friendly guy, and knows his stuff with Lotus twincams.

Alan.
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PostPost by: Jaylow » Sun Sep 20, 2020 9:06 pm

Thank you for all your comments. I didn't expect nearly so much help.

Stuart (69S4), I'm half way between Wallingford and Henley. My machinist wasn't FJ Payne though.

Foxie, thank you for the link on cam buckets. I can put the buckets into the newly machined sleeves with a 1.5 thou feeler gauge down the side. Looks like the sleeves are machined too loose.

Leslie, thank you for all your very helpful comments. Replying to a few; a colleague at work came up with the nick name J-Lo based on my initials, and it stuck, possibly because there are too many Jonathans in the business. Nothing to do with my name sake, although I do have a generously proportioned back side. As far as asking for references, I did get as far as composing a piece on getting help with what work I needed, but couldn't work out how to make a new post. It doesn't help that I don't generally use social media. I probably should have tried a bit harder! Deck height measured with some digital callipers is now 4.575 inches, whereas before I had measured it as 4.588. That's not to say I haven't make a mistake, either time. Cam follower buckets are new from Burton.

Nmauduit, thanks for the advice. Skim appears to be 13 thou to 4.575 inches, so not too bad, but like you said, they should have told me. This is the first work that I've had done to this engine, and the previous work for which I've records is gas flow, port and polish (about 40k miles ago in 1987). No idea if that includes balancing the chambers. Valves are new.

Steve, Thanks. I will try some engineer's blue to check the seal, or maybe see how water tight they are.

2cams70, sounds like you had a lucky escape. I'll get my second opinion to check the valve - guide clearance.

Wobblyweb and Mark, thanks. I think that is Exon Race Engines in Coalville, Leicestershire?

Alan, thanks.

Thank you all for your support. I think I'll contact the machinist and ask why they skimmed the head and to what tolerance they machined the cam follower sleeves. I'll try to find someone for a second opinion and report on the cam follower sleeves and the fit of the valves to guides and seats. Has anyone had experience of Oselli towards Milton Keynes or Classic and Modern Engine Services in Bracknell?
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PostPost by: alanr » Mon Sep 21, 2020 4:21 am

There are plenty of machine shops out there with a lot of experience but I would look for one with lots of Lotus Twincam experience.The rough alloy casting of the twincam head need specific and careful attention IMHO to get machine work done on it properly. Just because an engine shop has a good reputation for Classic BMC engines of the period, which are a totally different ball game, they may or may not be the right choice for working on a Lotus twincam.

Be prepared to travel would be my advice.

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PostPost by: 1owner69Elan » Mon Sep 21, 2020 6:07 pm

I understand the stock head height dimensions to be:

Small valve - 4.638 / 4.643
Big valve - 4.598 / 4.603

For example, the head height on my new SAS Weber head is 4.64.

So, if your measurement is correct at 4.575, it would appear that the head may have been resurfaced more than once. May have a further effect on compression ratio depending if other elements not changed (pistons, gasket). Also, valve - piston clearance will have been reduced with a "thin" head - not sure if that is a problem in your case.

Maybe some of the experienced engine builders on here can provide a better perspective.
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PostPost by: Famous Frank » Mon Sep 21, 2020 11:19 pm

Jaylow,

I certainly hope your head and engine are okay and that it gives you years of trouble free service. There are not many engines that can put a smile on your face more than a good running Twincam!

If I may, I would like to use your thread as a reminder or learning experience for anyone contemplating having machine work done on their Twincam. Ask for references before hiring someone. Here in the states, I can count on one hand the people I would let touch one of my Twincams. I remember 40 years ago having head work done. The shop was very reputable and honest but all their years of experience was on American V8’s and 6 cylinders. They had never seen a Lotus or Jaguar head before. By the time they gave it back to me it was trash. Luckily that was at a time you could still buy a used head for a reasonable amount of money. When they returned the head to me, they said they would reimburse me for the amount of me buying another used head but they also said they would never touch another one. They knew they screwed up.

Today is a different story. It’s not easy or inexpensive to find good used cylinder heads. Many have been machined to within an inch of their life. New ones are available but your kids may not be able to attend college.

Best of Luck! Happy motoring!
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PostPost by: Jaylow » Tue Sep 22, 2020 8:24 pm

Famous Frank, by all means. I hope something positive comes from my experience.
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