Cylinder head refurb..

PostPost by: djb222 » Wed Jun 06, 2018 3:10 pm

I've just dismantled the cylinder head from my engine...and have a few questions....

The valves and the head have fairly heavy deposits of carbon...what is the best method of cleaning off the deposits?

The diameter of the valve stems are uniform along their length, however there is a slight lateral wobble when located in the guides.

The inlet valve seats are good, the exhaust not so good...see pics.

I would certainly like to rebuild the head myself...any advice greatly received. David

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PostPost by: ericbushby » Wed Jun 06, 2018 4:07 pm

David,
My advice is to obtain a copy of Miles Wilkins book,---Lotus Twin-Cam Engine.
Brookland Books are showing it in stock.
I am inexperienced with engines,but found this to be a great help and it guided me through the process giving me some confidence that I was doing it correctly.
I have the skills but you need knowledge as well to be successful.
Best of luck
Eric in Burnley
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PostPost by: bill308 » Wed Jun 06, 2018 4:20 pm

Hi David,

I admire your willingness to rebuild your head, yourself. However, if you can wobble your valves, the guides need to be replaced and honed for proper clearance. This requires special tools. If the guides are replaced, the valve seats will need to be recut to make them concentric with the new valve axis. Again, this requires special tools. The other things to be checked are the head gasket surface, which may need to be skimmed, cam follower bores, and a leak check. Almost all tasks require special tools not normally found in the DIY tool chest.

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PostPost by: djb222 » Wed Jun 06, 2018 4:37 pm

Yes, that's what I was thinking, replacing the guides is a little beyond diy. I'm happy to reassemble and send the head for refurb.
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PostPost by: StressCraxx » Thu Jun 07, 2018 1:12 am

It's possible both the guides and valve stems are worn. New stems may not provide the desired clearance. The seats will require grinding to the new guides.

A good shop with Lotus twincam experience is invaluable. There are lots of other things for the machinist to check when you refresh a head.
There is no cure for Lotus, only treatment.
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PostPost by: Bigbaldybloke » Fri Jun 08, 2018 1:03 am

As a reasonable amateur mechanic, I?d say get a specialist machine shop to replace the valve guides, recut the seats and if necessary a small skim on the head, then do all the reassembly work yourself. Take your time, read the manual and if you have it the Miles Wilkins book on twin cams, and stand back and admire your finished work!
Change is inevitable, except from a vending machine!
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PostPost by: djb222 » Fri Jun 08, 2018 8:25 am

That's what I was thinking. I've got a copy of the Wilkins book and the manual. I have two good engine workshops relatively close, Wilcox engines and John Smithiwaites.

I can see from an examination of the head that it has been worked on before, it now has big valves fitted and at least the inlet ports have been gas flowed ( even the inlet valve guides have been cut back inline with the port. The exhaust ports are covered in carbon, but most likely have been gas flowed too.
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PostPost by: elanman999 » Fri Jun 08, 2018 10:14 am

In Wilcox and JS you have named two good shops. Do not be tempted to use anyone cheaper.
Cheers
John
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PostPost by: djb222 » Fri Jun 08, 2018 10:20 am

I had a good chat with JS this morning and he actually offered to pop over this weekend an have a look at the head and the block.
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PostPost by: 2cams70 » Fri Jun 08, 2018 11:35 am

You really won't save much money doing the assembly yourself. As has been said the main work is in the machining. There's nothing to it once everything is correctly machined - just popping the valve springs on and setting the clearances. Better for them to do the whole lot and provide it complete and ready to bolt on. That way should anything go wrong it will save arguments as to whose fault it was. The stuff that Wilkins describes - removing and replacing valve seats, removing and replacing tappet sleeves, etc. is best left to professionals. It will all require final machining in any case. The last thing you want is to drop a valve seat and totally destroy the engine. Make sure they check the sleeve to tappet clearance and the valve spring tension also.
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PostPost by: Chancer » Fri Jun 08, 2018 2:48 pm

It can be done by hand, without machinery and with only one special hand tool and I did several back in the day but given todays value of a cylinder head, the superb precision tooling that the pros use I would never again knock guides out and in with a stepped pin punch drift and recut the seats with my trusty Sykes Pickavant universal valve seat cutter.
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