CAMSHAFT GEAR MARKINGS

[redskatejbf]

Can someone tell me which gear is the inlet & which is exhaust?
I have two new unused gears that I bought some years ago, one has the alignment mark corresponding to the root (bottom) of the gear tooth, the other gear has the alignment mark inline with the middle of the tooth.
Neither of these gears are marked Ex. or IN. so I do not know which camshaft to fit them on.
Many thanks, John.

[neilsjuke]

If you get the cams in No1 firing at TDC you should be able line up the marks to sort it out.

[bcmc33]

The Miles Wilkins book shows the inlet mark on the tooth and th exhaust mark on the root.

[redskatejbf]

Thanks for the info.

John.

[Gra-ham]

Hi John
Lucky you. I've never got the marks to line up even though the gears are marked IN and EX. There's always been a half tooth out. And this is on two motors (+2 and 7s4)! Thus it seems one cam is either ahead or behind of where it should be. Now I know why. Looks like it's covers off to check where the markings are. And yes the chains have the right number of links and new ones match the originals.
Cheers
Gra-ham

[redskatejbf]

Hi Gra-ham, If / when you take the cam cover off could you let me know which marking is at the root of the gear or through the centre of the tooth, or if they are both marked the same. I took the cam cover off my engine to check the markings ( to compare them with my spare new ones), broke the gasket, and then had the thought as I`ve got this far I will check the valve clearence!. All the inlets were a bit tight and two exhaust also on the limit, so a quick simple job turned into a pain in the rectum. Be warned!!!!

Regards John.

[Gra-ham]

My +2 cam sprockets are both marked at the bottom/root of the tooth! The reference earlier in this topic to the Miles Wilkins book should be used. It seems I have two exhaust sprockets and perhaps the inlet sprocket may be driving the jackshaft. I'm not removing the front cover to find out!
The spigot on the end of the camshafts on my engine locates in the middle hole of three in the sprocket.
With TDC on No 1 cylinder the markings should line up with the head top surface. Both lobes for number 1 cyl would then be pointing outwards and for No 4 cyl they are pointing inwards towards each other.
I have checked the inlet opening (26 degrees BTDC - standard cam for my motor) and the exhaust closing (26 degrees ATDC) settings on number 4 cylinder when number 1 cylinder was on the compression stroke. By using my smallest feeler gauge and testing where the opening (or closing) of the valve occurs and then checking the position of the TDC mark on the crankshaft pulley relative to the TDC mark on the front cover, I can verify the approximate correctness or otherwise of the camshaft position. Rotation of the camshaft by one space between teeth is equal to 20 crankshaft degrees so one sprocket tooth out is very obvious.
I hope this helps.
Gra-ham

[redskatejbf]

Thanks Gra-ham for your reply.

[alan]

All Exhaust sprockets are marked EX. If the sprocket is not marked, it is an inlet sprocket. It's as simple as that. It's nothing to do with if the line is at the bottom of the teeth or the point of the teeth.
The EX is etched with a hand engraver.
I hope it's been of some help
Alan

[john.p.clegg]

What is the difference between the exhaust ,inlet and idler shaft sprockets....or is all snake-oil?

John

[CBUEB1771]

What is the difference between the exhaust ,inlet and idler shaft sprockets....or is all snake-oil?

John,
The two sprockets are subtly different. I just placed an exhaust sprocket on top of an inlet (both with alignment marks up) and rotated them until the bolt and dowel holes lined up. The teeth also ended being exactly in phase. The difference is that the alignment mark on the exhaust sprocket is rotated exactly one tooth clockwise with respect to the timing mark on the inlet sprocket. Both timing marks are right in the middle of the "valley" between two teeth. In other words the sprockets are identical except for the placement of the alignment marks. As Alan points out the exhaust sprocket is marked with a hand engraving. Lotus would not incur that expense if the sprockets were the same. The jackshaft sprocket has no timing mark at all, not needed in the Twin Cam application.