Hello Nick, why you want to know that?.
In the case where you want uprated your camshafts?.
measure std for 5/16 lifting : 36.10mm
measure std for 3/8 lifting : 35.90mm
They are the same !. Except below the cam.
This is the A measure .
Note , when you want increase the lift for more horsepower, you must remove material under the cam. That is what did Jaguar.
You want a lift + 0.50, remove 0.50 beneath. Of course change the motor game pads.
Be indulgent about my language… i am French!.
But i have 50 years of mechanical uprated.
thanks…the reason to want to know the measurement…heel opposite to lobe, to the lobe tip…on a as when new cam…is to easily check for lobe wear on a used cam. Thanks Rob…nice graphic. The depth gouge shown can only be used to measure “C” when cams are removed. The “A” measurement is the one I want for the several cam part #. Yes the “lift” spec of the cam should be A-B. Note that lift is NOT the same as how much the cam lobe moves the valve via the tappet…because there is clearance of whatever the spec used is.: .commonly either I-004/and E- 006: or 006/008.
Anyway…I just want to know the heel opposite lobe to the tip of lobe measurement…easy peasy . Dimension “A”. in the schematic. Once known any cam can be quickly checked.
Nick
so a bit different but still on cams and I am no expert: so…peer comments and verification requested: …Clearance not only affects lift…but also when the shape of the lobe starts to move the tappet to open the valve, …and after tip contact, then starts to “undo” that to close the valve…so it affects duration and rate of open/close as well. On some hi perf V8 engines tests were done changing only the clearance…one side at a time, then both…lesser and greater to see how dyno tests changed. (TV show “Engine Masters”). (not a OHC engine…it was rocker pushrod which has a ratio involved).anyway…the Results : More clearance, which means less valve lift…did better on exhaust. ohh looky, Jag specs are for more exhaust clearance…up to .010 on WOT race applications. Some think the exhaust valve should be more open…to let exhaust out and cool the valve. Jaguar in the day, engineered the head with Weslake, Heynes, Lofty England et al…and certainly intake ports, cam lift and profile were studied…thus the small but important revisions in the C Type head. C7707. I am only interested in Jaguar factory cams, for Jaguar factory cylinder heads.
so…who has cams visible to be measured.: the .lobe tip, to the opposite side…Measurement “A” in the diagram. That and the cam Cxxxx part number. A few have been listed…but not enuf to make a accurate conclusion. Nick
That’s great graphic. It also shows that the stock cams begin to move the tappet when they contact its extreme outer edge. For this reason, installing an aftermarket billet cam with greater lobe lift, i.e. heel to nose greater than the standard dimension, requires first installing larger diameter tappets. Otherwise, the cam nose hits the tappet guide first, not the tappet.
Somewhere, I’ve seen a diagram of how they they fix that: they cut a notch 180° across the tappet guide, in alignment with the lobe.
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as you noted Mike…the lobe strike against the guide can happen with a higher lift cam…AND…in earlier XK engines the guides were not chamfered…and a 3/8 cam can NOT be installed in early engines with a 5/16 cam and the early guides…The lobe WILL strike the guide. There is a service bulletin about that.with the engine number of when the change was made, and also instructions for modifications needed if one were to attempt such a replacement…
so…another reason…it’d be good to have the heel opposite lobe, to lobe tip dimension of the 5/16 and the 3/8 cams. Anyone? Hey…someone has to have some cams on the shelf…Bill Basset? Dick Maury, Roger, Rob, Peter C ???
Nick
while on cams…the diagram helps understand…“flat tappet cams”, yes the tappet is flat, but it is also the cam shape with a much flatter side profile and a pronounced lobe. ZDDP has polar molecules and is attracted to the steel, it forms a sacrificial layer…a barrier to metal wear. ZDDP used to be in motor oils…today it is in far fewer ppm if there at all. 1100-1500 ppm is what is needed. This is diffcult to mix yourself by adding ZDDP to a modern oil…and some already have a little…so how much to add is almost unknowable. Too much is also not good. There are now oils with manufacturer zddp.listed as for classics or hot rods. Either way, zddp should be used. It is true that the XK valve spring pressure is low compared to V8 hot rod standards…but cam wear can happen very quickly. Another factor is the “cling-ability” of the oil…how much does it remain on the cam and follower, how much does it remain under pressure from cam to follower contact. These are two different things, and not often specified. Plenty of info available on the web…just look up flat tappet cam problems/wear. Which gets me back to…what is the as new dimension of “A” in the diagram? A thought: if cam lobes are worn by say, 2/1000…would a thicker adjusting shim…by 2/1000 correct that…by moving the follower closer to the lobe?
Nick
These measurements are from some loose cams I have in the shop. Unfortunately, I took two heads, Mk10 and e-type, to the machine shop last week along with my extra set of later cams, so I only have the early stuff right now. I will (hopefully) have something back I can measure for the later cams in a couple weeks.
These measurements are heel to lobe tip x width
C5717/C5718 xk120 cams which I think might be the performance “M” parts
1.425 x 1.042"
loose early intake cam - number not visible, but has a cable drive dog, so pre-tack drive
1.360 x 1.041
pair of Isky cams (xm-2) which came with my 120 - car had been raced in the Buffalo NY area by po
1.383 x 0.963
I hope this helps some with your question.
I posted this information on the XK forum recently.
This first one is stamped C.2444 in very tiny 1/16" characters and MC20889A in larger 1/8" characters, both at the front end. It has a bolt and oil thrower flange on the tail end, confirming that it was used on the intake side.
A - B = Lift in inches
1.360 - 1.044 = .316
1.362 - 1.043 = .319
1.362 - 1.043 = .319
1.362 - 1.043 = .319
1.360 - 1.043 = .317
1.360 - 1.044 = .316
This second one is stamped at the front end in 1/4" high characters C.2237 on one side and C.2444 on the other side; it really is, with no MC numbers at all. How would the factory assembler know which it is? The tach drive is missing, but the position of the front lobe in relation to the alignment notch confirms it is an exhaust cam. At the tail end it is stamped SE in 1/4" letters, though why is not clear.
I suspect it is a first generation C.2237 exhaust. Was somebody trying to grind it down to be a higher lift and then stopped? Maybe, just a guess.
1.330 - .983 = .347
1.360 - 1.043 = .317
1.357 - 1.033 = .324
1.360 - 1.043 = .317
1.312 - .970 = .342
1.360 - 1.041 = .319
One from XK140 engine G4686-8S stamped C.5717 in 1/16" and MC20889E in 1/8" letters.
1.426 - 1.044 = .382
1.422 - 1.043 = .379
1.423 - 1.041 = .383
1.425 - 1.041 = .384
1.424 - 1.045 = .379
1.423 - 1.046 = .377
The other one from G4686-8S stamped C5718 in 1/16" and MC20889G in 1/8" letters.
1.422 - 1.041 = .381
1.423 - 1.040 = .383
1.423 - 1.040 = .383
1.425 - 1.040 = .385
1.423 - 1.040 = .383
1.423 - 1.041 = .382
thanks for the data Ron…I am putting all together…and will share. The C5717, C5718 are the XK120 special equipment package (S) cams which then later became standard, they have 3/8 lift. Were the Isky cams installed in the car or spare parts when you got it…?Nick
thanks Rob, forum rules require 20 characters in a reply…so I typed the rule…Nick
The parabolic camshafts, the reason why per the (S1) parts catalogue the XJ6 camshafts „MUST both be removed and the newer ones fitted“, plus the decal with the new valve clearance (which also applies to later E Types), were introduced 1969/1970. Not that it helps but in case someone was curious.