Lotus Elan

Camshaft Timing

PostPost by: Rowge » Thu Dec 21, 2023 6:32 pm

Hi All, long story, head rebuilt, cam timing exhaust now MOP 110, Inlet MOP 105, car was running rough exhaust cam was 2 teeth out prior to head rebuild, is one tooth on the camshaft 5 or 10 degrees.
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PostPost by: Hawksfield » Thu Dec 21, 2023 6:47 pm

Rowge

Are those mop settings at present and is it running ok
What did the timing marks look like when the exhaust was two teeth out.

John
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PostPost by: Rowge » Thu Dec 21, 2023 7:39 pm

I won the car from Bridge Classic cars, Car was running rough on idle, and smoking badly, the car is lovely apart from the head had been badly rebuilt in South Africa , wrong valve valve seals etc and exhaust valves deep into the head with very thin shims. Rebuilt the head using standard parts from QED, valve guides, seats etc, set up cams as before and the exhaust valves hit the pistons when turning by hand. Another set of exhaust valves fitted, D spec cams but non original sprockets, now have 110Mop on exhaust and 105MOP on Inlet, no 4 as in Miles Wilkins book, not sure how to get 110 on Inlet ?
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PostPost by: ncm » Fri Dec 22, 2023 10:13 pm

To alter the camshaft timing you will need to use either a set of vernier gears (£££) or offset dowels :- https://qedmotorsport.co.uk/product/cam ... s-offsets/

Brian.
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PostPost by: rgh0 » Fri Dec 22, 2023 11:54 pm

There are 34 teeth on the cam sprockets and 17 on the crank sprocket. So each cam sprocket tooth represent 10.6 cam degrees or 21.12 crank degrees.

It is strange for the inlet to differ that much from the exhaust as their relative postion is set by the distance between them wihich is a fixed number of chain links. I would start by double checking everything to confirm the parts are correct and you actually have a true 5 degrees MOP difference. One or both of your cam sprockets may be incorrect or worn.

Machining of the head and block and changing the distance from the crank to the exhaust cam sprocket is the normal cause of the need for offset dowels or adjustable sprockets and then you need to adjust the inlet to match the adjustment done on the exhaust sprocket.

Offset dowels are normally sold from 1 degree to 10 crank degrees which covers the full range of 20 degrees needed to offset the 21 crank degrees range between teeth by setting them in a forward or back ward direction as needed.

I used offset dowels for many years but found them difficult to use and slow to set accurately. You also need to be careful not to drop them down the chain cover when fitting and removing !. I use adjustable sprocket these days as much easier and quicker to set up.

cheers
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PostPost by: Rowge » Sat Dec 23, 2023 9:33 am

Blimey thanks for the information, using a copper 0.030 thou gasket, had ex 110 MOP, and Inlet 105 MOP, just fitted the head using a new 0.061 thou Cometic gasket, had to trim it and remove a rivet around the breather pipe/o ring, now have ex 115 MOP and Inlet 101 MOP, so am going to order some vernier pulleys from QED, once again thanks for the reply, Merry Christmas
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