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Cams & valve clearance

Cams & Valve Clearance

To all: And here I thought it would be a snap to reassemble the head; you know, like the manual says, "the reverse of disassembly". Ain't so. Aside from having a life outside the garage, the reassembly is actually going pretty well. So why am I here asking for more help? Some strangeness has come up. To do the job right, I need some guidance. First, keep in mind that although the car is a 140, the engine is a 1957 MK1 #KE-1610-8. Also, before I took the head apart, it ran very nice with the cams it has, right or wrong. Here is the strangeness. My cams have these numbers: intake-MC20889-E (in the casting) and C1308? (stamped) exhaust- MC20889? C13080. XK's Unlimt'd Catalog has this number listed for ALL 6 cylinder engines thru 1967: intake- C14985, exhaust- C13081. The 140 parts catalog has these numbers: intake-C5717; exhaust-C5718 (I'm not sure what value this info is since my engine is not from a 140) I need some opinions. 1. What is the best valve clearance for my engine : 1957 MK1 #KE-1610-8. 2. Does it make any difference what cam is in there as long as it works? Could the part numbers fom the XK's catalog just be generic cams that will work on anything? I don't intend on racing this car. Just getting to the corner and back will be a real show stopper. 3. Some of the adjusting shims I need, now that the valve job is done, are thinner than the thinnest ones in the parts book; .079 and .080. I'm having the shop make some special. Is this going to cause a problem down the road? I have the spaces set at .006 for both sides now. The remaining ones are waiting for smaller shims. I hope the format of this letter doesn't get all messed up in transmission. Thanks, Aloha Rob XK-140 FHC

Rob, My XK120 unfortunately has a MK I head. I set the valve clearances at .004 and .006 fot the intake and exhaust after a recent rebuild. No problems to date. It also had some shims in it in the .070 to .085 range. These shims were in the head for about 6 years and 15000 miles with no problems. I had to replace the valves and seats to get the clearances correct during the rebuild. The valve tips have a small area of hardened metal. I remember it being about .005 or so in depth that can be removed (it's in the manual). If you remove too much, the shim might not sit on top of the valve and sit on the retainer ledge instead. This could allow the keepers to loosen and allow the valve to fall into the chamber. Hopefully, I didn't confuse you. - Cleo Bay Jr., 52 XK120 OTS, 56 XK140 OTS

Rob, Jag cams. Scares everyone. Jaguar only had 3 sets of cams for their street XK series engines. The part numbers are always preceded with a "C" for engine/transmission parts and "BD" for body/chassis parts. The P/N's are the ones that are stamped in the smoothed section of the cam near the #5 cylinder. I don't recall that Jaguar ever cast any P/N's into their parts. I did a posting a while ago of all the P/N's and applications, but I didn't save it. The early ones had a 5/16" lift and the "S" cars came with 3/8" lift cams. They then drilled the base of the cam lobe to make them quieter when cold. All used the same timing spec. In late 1968, they modified the cam ramps and no longer drilled a oil hole in the cam lobe. This was done in an effort to save money. The latter cams have the same lift, 3/8", but because of their changed ramps, actually have a longer duration and would be a little higher performance than the earlier cams. They also changed the clearance requirements. Use the stock clearance requirements for your engine which should be the same for a 140 or 3.4 sedan. By the way, officially, there is no such thing as a Jaguar Mk 1 sedan. That is an americanized ID just like the XKE for an E-Type. Your machine shop should have cut the seats and valve stems so your shims would be very close. Stock shims ran in 26 sizes from .085" to .105". The reground performance cams reqire a thicker than stock shim because they grind the base of the cam lobe to achieve more lift. You can grind your shims to whatever size you need. They are hardened all the way thru. Hope that helps. - George Badger

Hello Rob, that happens very offten, that the gap between the cam and the valve gets too thin after installation of new valves. Instead of fitting thinner shims the right procedure is to measure the gap. Make notes about it, then take the valve out again and have a machine shop cut the valve shafts on a lathe accordingly. Sorry, there is no other appropriate way. Am I the winner of the heating bet? - Arno Wahl

Arno: Yea, I knew that. - Bruce Baysinger

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