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HEAD QUESTION (valve protrusion) - Engine/Ancilliaries - The Lotus Forums Jump to content
giorgio67

HEAD QUESTION (valve protrusion)

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Hi all guys,

can't find anything about that so i would like to ask you if there is a reference measure for the valves protusion on the head for the 912 engine.

Just had a look on my freshly rebuilt head and they seems a little bit too protruding for me, (the inlet only).

The head has been skimmed and fitted with new seats, springs, guides and the Garry Kemp bigger set of inlet/exhaust valves set.

Thanks for your help, I'd like to check them.

Giorgio

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Giorgio, you should be OK, but never leave anything to chance - to measure piston to valve clearance you will need to carry out a trial build.

Basically install everything, pistons/valves/head etc, but put a small strip of plasticene in the piston cut outs (don't forget to lightly oil the plasticene to stop it sticking to the valves), before you fit the head, and set cam timing.

If you've kept the old headgasket, and it's serviceable for this task, it will save you sacrificing a brand new one.

Turn the engine over gently a couple of times by hand - stop if it meets resistance.

Remove the head and you'll see valve marks in the plasticene. To find out how close the pistons/valves got, slice the plasticene in half at the mid way point with a sharp knife. Remove one portion, and measure the depth of the portion remaining on the piston crown cut-out, with a depth micrometer.

Can't recall off-hand what min clearance should be, but if it's less than spec, you'll need the cut-outs re-worked to suit.

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Hi guys,

here some pics of the head/valves protrusion.

I will check piston/valves clearance for sure but take a look and tell me what you think about, I think it's quite common in a head fitted with oversize valves?

Fast checking with a straight rule shows protrusion of about 1,49mm.

Giorgio

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post-3419-0-12343500-1348751825.jpg

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Hi guys,

I'm very disappointed now.

I've sent some pics of the head to Garry Kemp, he sold to me the bigger valves set and I've just got his answer.

The inlet seats have been badly machined, so now the seats are sitting on the 30° angle and not on the proper 45° cut angle as they should be.

I've spent a lot of money for parts and labour on my head and now it needs to be re-worked...

I don't like the idea to ask at the men who did the job as I not trust him anymore, I'm think to send the head to Garry to have it properly checked and to have the problem solved.

Not a good notice, as every parts of the car is causing a problem in these days....the heads it's heavy and postage cost plus labour would be expensive I think :thumbdown:

sadly I'm not living near Maranello... and in my town there are not good specialist for the job.

I'm tired.

Giorgio

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Giorgio,

Go back to the guy that did the work with the information you have from Garry Kemp. Getting the seats recut from 30 deg to 45 deg is not difficult. It is done by machine. It is not so much a matter of 'badly machined' as you have put it as 'incorrectly machined'. The rest of the machining work etc on the head looks quite good so it may have just been an error of not checking the valve face angle prior to work.

If too much material is gone and the seats need to be replaced (unlikely, I would think as the excess material will be at the bottom of the seat) then that will be at his cost as he made the error.

As you are now armed with the correct information, going back and asking for the error to be rectified should not be an issue.

Best of luck. Keep us informed.

Michael.

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I'm tired.

Giorgio

That's why restoration projects are rarely finished by the guy that started them & those that do take years & deserve respect. :respect:

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Michael,

.... so it may have just been an error of not checking the valve face angle prior to work.

These are things I never understood sorry.

How it's possible?

It's his job, his job is to do engine heads, just heads no other, I don't trust a person that is not able too see what he's doing.

I'm a little bit harsh sorry but if I need to tell him how the job must be done...I think my head is not in good hands anyway...

Giorgio

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The issue of familiarity. Assuming he 'knows' the angle 'will' be 30 deg, 'because they all are' or perhaps he deals with heads that are mostly the same angle on both exhaust and intake.

Take the head back, armed with your information and see what he says. If you decide the head will be in 'bad' hands, ask for a discount on the work as he has made a mistake.

You may find, he is oblivious to the error initially and may well be sincere.

You have nothing to lose other than some time and everything to gain.

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Chin up Giorgio.

Like said above just because the man got it wrong doesn't make him bad. Engineering is never a straight job and you will find out how good he is when you explain your issues with him.

Dont despair yet!

Buddsy

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Have a look at this, Giorgio...it's about American V8s but the principles still apply....

http://www.enginebuildermag.com/Article/2586/high_performance_valve_jobs.aspx

Multi angle machining....ought to be able to do that to your head, adding the 45 deg and 70 deg angles to the existing 30 deg one.

NOTHING is ever simple, is it? But we press on regardless....

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Giorgiou, do not lose heart my friend, having seen your pics, my first thoughts were that your valve seats hadn't been cut to match the valves. This would be more evident when you come to lap the valves in a there would be a v narrow grey band as the contact point. As has been suggested go back to your builder and get him to sort it.

If it is any consolation at every turn my engine build has given me grief. I've nearly chucked the towel in several times, but I'm now resolved to complete it. As they say nothing worth having was easily had

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