Help needed to identify my camshaft marked MC
The early ones were marked with a Ā© and your MC was supposed to be āmodified competitionā. Higher lift, more duration? Other experts will jump in and prove me right or wrong. I had an early car, 54 drophead and we re-did the head, and the cams were marked āCā. Pretty sure that was just the stock designation.
That numbers is just a forge number for the rough cast item and to a certain extent means nothing until machined once machined to what is becomes then a part number is stamped in C#### then this tells you what it is and for
1 Like
The Cxxxx part number is stamped in very tiny numbers between two lobes, usually very hard to read.
But there are some exceptions where it is in very large numbers.
1 Like
I pulled 5 cams, more or less at random. All of the cams whose lobe heels were drilled for oiling had the same MC 20889 plus a suffix. This was true regardless of intake or exhaust origin. Cams without the heel drilling did not have the MC 20889 mark.
the XK120 was factory built with , early, the 5/16in lift cams int C2444 and exhC2237 or later (SB109) with the 3/8 lift cams C5717 inlet, C5718 Exhaust. (The Mk7 used int C4488 or later C4489, and exh C2237 and later C4038) As Rob said these C part numbers are tiny and near the cam front as shown with the C2237 photo. So these C part numbers are the ones you want to find to identify a cam. There are many important details to cam/valve train replacement parts being later installed. From eng #W4483 onward the 3/8 could be after-market fitted without having to make essential necessary modifications to the valve guides. (SB95 and SB105 and SB108)) Note that valve springs for the 3/8 were improved from W9487 . and the new spring was suitable for replacement in full sets for either cam (SB129). See also SB149 re new inlet valves (refer to SB142) with a thicker valve head, also requiring special modifications if installing on prior engines. Clearances also changed SB132. and SB140). See SB142 for fitment precautions. See SB147 for āclatterā issues and fix modifications. ALL of the cams with the MC #s I have seen are LATER installed cams, with much later manufacture times. As said the MC #s are a manufacturing cast lot and DO NOT mean "MC as in āmodified competitionā. There was not a XK120MC. There was a XK140 referred to as āMCā by the unwashed masses. It has been recently found (Roger Payne) that perhaps indeed a few XK120s left the factory with an early āCā head, (Urs says from April 1953) the cams being the then standard 3/8 lift with the same cam C part numbers. āCā heads (C7707) became available from the factory as spare parts and could be installed after-factory by owners/shops. (SB65 is of interest as an early procedure for setting valve timing via the cams). The usual suppliers have various cams for replacements, some reground, some new billet. An important measurement on any used cam is that of the cam lobe peak, to check for wear (a āflatā cam).( Iād like to list that hereā¦but have to search my notes for it.)
As you can now see there are many aspects to servicing components that REQUIRE observation of the Service Bulletins which revise what is in the Factory Service Manual.Clearaces are your choice of the 2 factory specs for street use (.I-004-.Ex 006, or the .I-006-,Ex 008) nwhich āseemā to have been revised more to noise issues rather than performance, with the exception of the race wide open throttle only specificationā¦I- .006-.Ex 010) Nick
Thank you to all the knowledgeable people on here.
The car is a factor wire wheels car with racing history. I have been told that the later G cylinder head was fitted before the second owner purchased car in 1957.
makes sense it would have later camsā¦look for the teeny Cā part #sā¦orā¦whenever cam covers are offā¦look, but also measure the cam lobesā¦heel to lobe with a fine caliper. That dimension spec escapes me at the momentā¦perhaps someone has itā¦for 5/16ā¦and for the 3/8. There are of course regrinds and other duration shapes possible than stockā¦especially if once a race car. Check sometime on what distributor you haveā¦and if vacuum advance is hooked upā¦often not so if raced.
alsoā¦is proper thermostat in place. also often removed with a blank off to bypass if raced. Usually other signs in air ducting to carb and brakes, etc. Nick
The G serial number indicates it is from an XK140, but could be a standard A type head. If it has a big letter C in the middle of the valley, that is a C type head, as many XK140s had, and was a common modification back in the 1950s for 120 racers.
Wow that is wonderful how did you make the collage?
I did a chart a while back listing all the cams through to early 1960ās whilst I was sorting some out looking for a pair Will try to get it typed up
Sober, I took photos of the part numbers on the first cams I picked up. Had a couple of home-grown Covid Margaritas and somehow created a collage. Prior to the Margaritas, I couldnāt spell Margarita. Err, couldnāt spell college. Or Collage. Whateverā¦ 
1 Like
Somewhat seriously, I think I used a free version of the PicCollage app on my IPad.
Nick, the actual Build Sheets for the XK120C (or C-type) competition car shows being equipped with C.5717 (Inlet) and C.5718 (exhaust) 3/8" lift camshafts - this is as of 1951 and unchanged up to 1953 revision, so will include both works cars and production cars.
The āfewā - actually so far FOUR only confirmed by me after a LOT of effort - with help of course - (not all 9:1 piston engines) - XK120s factory fitted with C-type heads, I havenāt been able to confirm current camshafts in all, let alone what was fitted ex factory, but relevant is all were specially ordered/prepared cars by the Jaguar Competitions shop for intended racing, so their exact factory build cannot be guaranteed as all are 1953/54 cars when Jaguar was indeed experimenting with amongst other things - camshafts - albeit in the absence of any proof otherwise, you have to presume still C.5717/5718.
But similarly its anyones guess what Camshafts were fitted to other Competition Department prepared engines, including the XK120s still with A-type heads and 9:1cr engines or indeed with 8:1 engines as these again are mostly 1953/54 when Jaguar was actively working on all aspects of engine developmentā¦
Roger, thanks for thatā¦which is why I both named youā¦and said āleft the factoryāā¦intentionally not sayin in production nor under what circumstancesā¦We do know the two sets of cams and part numbers for XK120 in production. Other later cams of course could b e fitted later as replacements at shops, with various fitment issues as to sprockets etc. I see the photo collage with C part numbers not related directly to the XK120 or 140ā¦so for Mikeā¦what is the car model application of those cams? I have never seen an XK120 cam with the MC xxxxxx markā¦only later of various C part numbers. Nick
1 Like
I just figured out how to do this with the native collage ap on my Android phone. It also works on a desktop PC in the Google Chrome browser.
On the phone, open Photos, go to Library then Utilities and select collage.
Itās more straightforward on the PC, thereās a Utilities button on the left side of the window.
Iām using a Pixel 5 phone and Android 11.
