Cams?

[Grizzly]

Hi all.

Just a little confused about which Cam is Inlet and which is Exhaust

I know it sounds daft but the engine bits where in a box all mixed up and after having a good look at the Cams and the Sprockets i can't find anything that says Inlet or Exhaust??

Just to add Insult to Injury, When i look at the Part Numbers they are both MC23929 B26E351 but one has an A stamped between the two numbers and the other has a B So there must be a difference??

It may well be that i'm tired and not reading the threads properly but it sounds like there both Inlet cams?? the thing that makes it even more confusing is the engine is the N prefix S4-Sprint Elan.

I only want to shim this up once

[AHM]

The cams are the same but the sprockets are different.

The exhaust cam should be etched with EX.

[Grizzly]

Think i have got it sussed after a bit of searching i found a picture of the Exhaust Sprocket laid over the Inlet, so once i knew which one was which all i did then was test fit the cams and as one had a slightly different profile it was quite obvious which shims had been used with which Cam

[alan]

both cams should have same profiles and all cam lobes same profiles.
If you have different profiles then the cams are not correct. It is a "Twin Cam"

[Grizzly]

both cams should have same profiles and all cam lobes same profiles.
If you have different profiles then the cams are not correct. It is a "Twin Cam"

Well if i measure up, the cam that fits the Inlet Shims best has 0.01 more lift than the cam that fits the Exhaust Exhaust Shims (the shims are not radically different, the inlets are between .109 - .120 and the Ex are between .097 - .110 so enough to be able to spot easily) i haven't gone into too much detail measuring the lobes etc but they are Defiantly not the same between Inlet and Exhaust (which is odd from what i've seen)

TBH i would not be surprised if this was just Cobbled together with odd bits because this Engine is allot rougher finished than my later Plus 2 (The head Casting is nothing short of Nasty), it doesn't help that i didn't strip it so some bits are marked and some aren't but one thing i can say without question this motor had Never been apart before it was taken off the road (one owner from new, he had it serviced by Lotus as he's not a mechanical kinda guy and he kept every receipt)

[rgh0]

The original sprint cams had two grooves on the hub the sprocket fixes to - do both your cams have that?

Orginal sprint cams also had a base circle about 0.01 inch smaller to produce the 0.01 inch higher lift ( .0.360 inch sprint cam lift versus 0.350 inch on standard or SE cams). Normal base circle 1.20 inch Sprint 1.19 inch. So its possible you have a non matched set of cams. What are the actual base circle diameters of your cams?

Of course also possible that one cam was reground due to wear at some time or maybe even reground in the factory due to a machining error when being produced.

I would check the lift and duration of each cam to check that it is the same.despite the base circle difference you have.

cheers
Rohan

[Grizzly]

After allot of measuring and messing about i'm more confused now

Yes they have the two lines so there Defo Sprint cams BUT!! where the Exhaust Measures exactly what you would expect for a Sprint cam the Inlet is just strange, it the base circle is slightly different but if you take that into account its still got a far bit more lift? It doesn't make sense if there supposed to be Matching??

But that said its running now and apart from a bit of a dodgy idle (probably down to needing a good set up) it lives