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MG TD TF 1500 - Identifying a cam
| It seems that cam doctors are now thin on the ground and because there is now no competition, the price to have a cam profiled here has doubled in the past 5 years, with the current cost being $100. I was wondering if there is some way of measuring a cam using a vernier or some other tool to get an idea of the identity of the cam. It is almost certainly one of three that were commonly available in the late 60's when the cam was most likely fitted. I do realise that an accurate profile can only be obtained using a cam profiling machine, but I'm only aware of one place now remaining here in Sydney. I had hoped that using some simple math, coupled with my digital vernier, I may be able to narrow down the field. Is this possible? Cheers
Peter TD 5801 |
| P Hehir |
| Is there no number stamped on the end? IIRC by the late 60's, early 70's all the Moss cams were high lift, not that this can really help you. |
| Christopher Couper |
| Nothing on the end Chris. Here's a pic. Cheers Peter TD 5801  |
| P Hehir |
| Peter The dimensions specified within the Woods document might provide a starting point. If the engine is fully assembled there is methodology to ascertain a cams characteristics, I dont think you want to enter that minefield. Only other thought would be comparison against another cam with known specifications. Graeme |
| G Evans |
| I'll check it out Graeme and give you a call. I can measure from the base circle to the top of a lobe but that's about it, unless someone out there has some other clever suggestion. Cheers Peter TD 5801 |
| P Hehir |
| The XPAG camshaft has such a small base circle it is almost impossible to regrind the profile. Tighe cams in Brisbane will grind you a new cam to your requirements using new blanks they have on the shelf. It's been a few years since I bought one, so not sure of cost - give them a call. Your flywheel is ready to post tomorrow Peter - text or message me your address please, I have an ear infection so hearing over the phone is problematic at the moment. Tony Slattery The Classic Workshop |
| A L SLATTERY |
| Thanks Tony. I look forward to getting my hands on the flywheel. I wasn't looking for a new cam, but just trying to identify the one that I have without having to visit the cam doctor. It's in great condition but I'd like to know what it is before I go to the trouble of fitting it. Cheers Peter TD 5801 |
| P Hehir |
| You have mail Peter |
| William Revit |
| On Bud Krueger’s TTalk site. There is a link written by the late Dave DuBois. There was also a discussion here maybe a year or two ago on camshaft identification that may help. You’ll have to do an archive search in 2018-2019 to find it. That article added info on the factory race cams and also if memory serves me there are machine marks that help to identify the original profiles. |
| W A Chasser |
| The fact that there are no rings on the cam end indicate it is not a MOWOG cam. So it seems to me that you need to find a knowledgeable cam guy, have the cam degreed and measured, and see how it compares to the stock .012 and after-market cams like the Crane 0002.
A knowledgeable cam guy can appreciate and discuss the ramifications of the changes from stock, pros and cons. I bought an NOS Crane cam thinking it was an 0002 or 0010, and when I had it checked over a cam guy laughed and told me its performance characteristics showed it was a drag-cam, and complete junk in a street engine. It was worth the money for that analysis. Tom Lange MGT Repair |
| t lange |
| A dial gauge, a lathe and a protractor should do the job ? Laurent. |
| LC Laurent31 |
| I only have one of the three though Laurent. :-) Thanks Willy. When you're back on line, you have mail. Tom the pic from Bob showed three or four cams. I can definitely eliminate a couple, except perhaps for the 4/44. As there are no identifying marks and as you've said; "and complete junk in a street engine. It was worth the money for that analysis." Sage advice. I almost purchased a used cam with lobes in great condition, however when the card finally turned up, it transpired it was a 38/78, 78/38! Lumpy and pretty useless in a street engine, unless you were intending to rev the guts out of it.. This is the last thing that I want to do. Longevity of the rebuild is my primary aim, which is why I went for the 4.3. I've had a couple of novel suggestions offline, one of which is to make an accurate profile of an inlet and exhaust lobe using thin white cardboard to fit over the lobe and use a dial indicator printed from the internet, with the cam on a couple of V shaped blocks to estimate the separation and to also measure the distance from the base circle to the top of the lobe. Sending this info to someone who knows about such things should help further eliminate known cams. The cam ran in Repco bearings when it was removed, which is something of a clue, raising the possibility of a local, possibly made to order job. The car idled smoothly when it last ran with this cam in 1970, so it isn't lumpy. As the bearings weren't Mowog and the absence of rings suggest likewise, unless the idea above works, or a better suggestion emerges, it looks like a trip to the cam doctor. I have plenty of time, but not a lot of the other, hence my desire to DIY, with a little help from my friends... Cheers
Peter TD 5801 |
| P Hehir |
| I went back into the archive seeking info on cams. I found the comparison of the various M.G. cams informative. What follows is from Neil Cairns. The first pair of numbers read as inlet opens BTDC, closes ABDC, then exhaust opens BBDC and closes ATDC.
MODEL CAM: TIMINGS: LIFT: PART NO: (if known.) SA 2 ltr Saloon, 11; 59; 56; 24. 8mm VA 1 1/2ltr Saloon, 11; 59; 56; 24. 8.4mm (later 11; 57; 52; 24) WA 2.6 ltr Saloon, 11; 59; 56; 24. 8mm 1147cc 10hp engine 5; 45; 45; 5. 6.5mm TA midget, 11; 59; 56; 24. 8mm X24084, MG862/171, AAA5776. TB & TC Midget, 11; 57; 52; 24. 8mm MG862/171, X24084, AAA5576. TD Midget & YT 11; 57; 52; 24. 8mm MG862/171, 168552, AAA3096. TD after TD2/24116 5; 45; 45; 5. 8.3mm AAA3096, 168553. YA 1 1/4ltr Saloon 11; 57; 52; 24. 6.5mm MG900/106. YA after SC/16831 5; 45; 45; 5. 8.3mm AAA3096, 168553. YB 1 1/4 ltr Saloon 5; 45; 45; 5. 8.3mm AAA3096, 168553. TF 1250 & 1500 5; 45; 45; 5. 8.3mm MG862/171, AAA3096, 168553. Wolseley 4/44 5; 45; 45; 5. 8.3mm AAA3096, 168553. Half-race; 13; 59; 50; 22. 8.3mm, AEG122, Full race; 32; 58; 60; 30. 8.3mm AAA3095. The overlap will no doubt be obvious to those familiar with cam design. For the rest of us it will be seen that valve overlap can be ascertained by adding the 1st and last two figures together. So with the TF 1250, 1500 and the 4/44 the overlap is just 10°. The TB, TC and early TD has an overlap of 35°, the half race 35° and the full race cam has an overlap of 62°. The 38; 78; 78; 38; cam I was offered for 'street use' has an overlap of 76°! Cheers Peter TD 5801 |
| P Hehir |
| The cardboard cutout idea won't work. Looks like a trip to the cam doctor is on the cards. Cheers Peter TD 5801 |
| P Hehir |
| Peter www.youtube.com/watch?v=FEeXtDnWy8w Copy and paste into your Browser, I think it commences to point you in the right direction. Graeme |
| G Evans |
| That will certainly appear to give me the lift Graeme. There does seem to be some difference of opinion on what the XPAG rocker ratio actually is, (certainly as far as the archive is concerned). If there is an incontrovertible answer to this question, (probably 1.5), then I can supply the cam lift based on the formulae expressed, (nose to heel - base circle x rocker ratio = cam lift). However I've just discovered that I can have an XPAG cam made here in Oz for $450 AU to any specification that I want! Given that it would cost me $100 to have a piece of paper that would then tell me what my existing cam is - which I may or may not want to use - OR spend the extra $350 and get a new engine specific cam, it seems like a no brainer. If I do go down the latter path then I just need to establish the specs. That's a whole other ball game... Cheers
Peter TD 5801 |
| P Hehir |
This thread was discussed between 19/05/2020 and 20/05/2020
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