View Full Version : Setting up a GP2 cam

02-18-2008, 11:10 PM
I have a Goodparts GP2 cam which I am trying to set up on my engine. I am really glad I have the engine on a stand - I would hate to try to do all this with the block in the car!

Basically, my problem is that I can't get any two of the tappet lift timings to match up. By now I am getting pretty good at adjusting the chain, thanks to the last several hours spent trying to work this out. As an example, my latest set-up gives the following (spec sheet values in brackets)

Intake valve
opening 0.010" - 29 BTDC (29 BTDC)
opening 0.050" - 2.5 BTDC (3.5 BTDC)
closing 0.050" - 47 ABDC (43.5 ABDC)
closing 0.010" - 77.5 ABDC (69 ABDC)
Duration @ 0.010" = 295.5 (278)
Duration @ 0.050" = 229.5 (227)

Exhaust valve
opening 0.010" - 66.5 BBDC (69 BBDC)
opening 0.050" - 42 BBDC (43.5 BBDC)
closing 0.050" - 7 ATDC (3.5 ATDC)
closing 0.010" - 40 ATDC (29 ATDC)
Duration @ 0.010" = 286.5 (278)
Duration @ 0.050" = 229 (227)

I am using a dial gauge mounted on top of the block (no head at the moment) to measure the movement of the push rod. I get 0.259" total lift (spec says 0.258"), so I figure I have the pushrod as close to vertical as I can get it.

I am perfectly happy to accept that I am doing it all wrong, I just can't think how at the moment. There is cam lube on the cam and the tappet, but I imagine after all the turning they have done in the last few hours there isn't a lot left. Any thoughts, advice?


02-19-2008, 06:58 AM
Whatever you do, Alistair, don't read my post on GP2 cams!

Been there, done that. Used a Kent adjustable sprocket to help fine tune.

The result after approx. 5K miles = a true enigma.

02-19-2008, 01:14 PM
Hello Alister,

I don't quite know what you are trying to get? Firstly what clearance should the cam be timed?

Are you aware that the Triumph cam can be adjusted to near enough 4 degrees which should be good enough unless you are running a racing engine so there is no need for an indexable timing gear. This is done by using one of the two pairs of holes (they are not drilled at 90 degrees to each other but give a half tooth variation). If that is not close enough, turn the wheel round this gives another half tooth variation. So the net result is a quarter tooth accuracy.


02-19-2008, 03:47 PM
Hi guys

Thanks for the replies, but I guess I wasn't clear what my "problem" is. I struggled to get the timing set up by using the different sprocket attachment holes, but just couldn't get it right. I figured I would be spending the money for an adjustable sprocket, but then I realised that with one of the settings spot on the other values were wrong. The duration at 0.050 tappet lift doesn't match the spec sheet, so how can I ever get it to match, even with an adjustable wheel? I guess I will call Richard Good tomorrow to see if he has any suggestions.


02-19-2008, 05:05 PM
From everything that I've read about degreeing a cam, and I just went through this last week on the TR3 engine, the most accurate reading is the one at 0.050" lift. That's the one you want to give most credence to. Also, if you have a choice, it's better to to favor a close reading on the opening of the valve then the closing. I don't really think you are very far off. Your openings are within 1 1/2 deg (I had to settle for almost 3). The closings are alittle more then the openings, but overall, I don't think they are bad.

Also, I made a 'dummy' pushrod machined from a piece of 7/8" drill rod. I cut down the end a little where it went into the lifter, and then wrapped that section with just enough masking tape so I had a nice tight push fit in the lifter. It gave me a real nice platform to take a reading from. One other thing is how you found TDC. There are several ways, but if done incorrectly, it could throw your readings off a couple of degrees.

A little inaccuracy here and there can account for some descrepencies. But overall, I think you're pretty close...closer then I got. /bcforum/images/%%GRAEMLIN_URL%%/smile.gif

Edit: The only figure I find way out of whack is the intake and exhaust closing at 0.010". That just doesn't seem to make sense, since it's pretty close at 0.050". My timing sheet didn't even include the 0.010" readings, only the ones at 0.050". Maybe that's why! /bcforum/images/%%GRAEMLIN_URL%%/hammer.gif

02-19-2008, 07:18 PM
Richard would for sure be the right person to ask.

But looking at Crane's generic cam timing instructions (Yes, I realize you don't have a Crane cam), I note that they repeat several times not to use the .010" values for timing the cam, only the .050" ones. From your numbers, I would guess that the .010" numbers include some small allowance for valve lash, while the .050" numbers don't.

Crane also notes to check base circle runout, and return the cam if it exceeds .002".

02-19-2008, 08:48 PM
Do you have the latest edition of the 6-Pack magazine? Kai Radicke has a great article about cam timing and the proper methods for a GP-2 on a TR6.

02-21-2008, 12:48 PM
Hello Alistair,

doesn't the cam set up give a figure for maximum lift at such an angle or is the cam wide lobed at maximum lift? The reason for the 0.050" setting figure is to get away from the quietening ramps on the cam.


02-21-2008, 01:15 PM
Hi guys

Thanks for the input. I spoke to Richard Good yesterday afternoon, and he suggested setting up with the "excess" duration either side of the spec values, i.e. a little advanced for the 0.050" tappet lift. I was planning to aim for a little advance to give more low down torque anyway, so hopefully this way it will give the right timing at full lift. Of course, with that plan in mind I went into the garage last night and the first attempt had the 0.050" lift values (opening) set up within 0.5 degree of spec but slightly retarded. I left it because it was so close, but I will probably just mark the chain/wheel position in case I want to go back, and keep trying to get a little bit of advance. I wish I had splashed out the extra for an adjustable cam sprocket!


02-21-2008, 01:39 PM
Alistair, I did buy the Kent adjustable cam sprocket and that slight bit of adjustability gave me exactly what I needed in dialing in the cam where I wanted it. Frankly, I have forgotten all the numbers (prolly because it gave me such a headache doing it) but I guess I will be revisiting all that really soon. For an amateur like myself, and with no help at all except what I could gleam from reading up on the internet, it took me days to figure it out. Now I have forgotten. Guess I will get the cam wheel and dial gauge out and start over soon.

Others find no need for the adjustable sprocket, perhaps they know all the tricks.

02-22-2008, 02:02 PM
Hello Bill,

fine for a racing engine which needs to be to the nth degree. 4 degrees accuracy on cam timing is quite acceptable for a road car.