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dklawson
04-08-2012, 07:38 PM
I have reached the point during the GT6 engine rebuild where I need to set the cam timing. I have new TR6 duplex pulleys and chain so I have no dots/marks/scribe lines to work with. Let me describe what I have done and please tell me if it is right. This is the abridged version.

I found true TDC and set my degree wheel to zero. I turned the crank forward in the normal direction of rotation until I reached 110 degrees, the LCA for the S2 cam I have. Then I turned the cam by hand until I found the max lift on tappet #2 (intake for cylinder 1) and fit the timing chain and camshaft sprocket. To check this I turned the engine in reverse PAST TDC, then advanced towards 110 degrees and confirmed I still had max lift on tappet 2 at that point.

Please let me know if I am doing this right. I am used to dealing with marked pulleys and it has been almost a decade since I degreed a cam.

Thanks,
Doug L.

DougF
04-08-2012, 11:01 PM
The one thing we didn't do was figure in valve lash with the dial indicator. The lash for my cam is .16, but as it turned out the stock lash of .10 was what worked.
If your intake and exhaust numbers are working out on the degree wheel and dial indicator, you should be good.
You can also use the valve overlap method that Isky recommends. The information can be downloaded on their website. They claim you will get optimal perform with this method.

dklawson
04-09-2012, 07:04 AM
I was unclear. The head is not on the engine. I am not used to setting the cam with the head in place. I am basing what I am doing strictly on cam/tappet lift and crank position.

All I have at this point is the cam angle of 110 degrees and the simple specs that say the intake opens at 31 degrees and closes at 71 degrees.

CJD
04-09-2012, 07:36 AM
Hey Doug,

What you did will work to get the teeth in the correct position. The only thing I may add is that the lifter movement at max lift is very slow, and therefore very difficult to read the exact point of max lift. I am sure you noticed this.

If you are actually degreeing the cam to perfect alignment with the crank, better check is to use a point of lift on the opening ramp of the lobe, and the same lift on the closing side. The center of these two crank positions should be your 110 degrees. For example, using a dial indicator on the lifter, turn the crank until it shows .1" lift on the opening side of the lobe. Read your degree wheel position. Continue turning the crank past max lift until it reads .1" on the closing side of the lobe and read that crank position. When you avergae the two crank readings, you have the exact center of the cam timing.

So, if you are just setting the cam to the proper position, what you did is the way to do it. If you are "blueprinting" to get the cam perfect, use the method above to get exact measurements.

John

dklawson
04-09-2012, 08:24 AM
Thanks John.

I was hoping that TSI would have specs for the cam that told me where to make those measurement (i.e. for 0.050" of lift the cam should be at X degrees). I am waiting to hear from Ted to see if he has those figures.

I have used the method you listed above with an arbitrary amount of lift each side of the lobe profile and I am sure that works well with symmetric lobe profiles. However, I don't know if the S2 cam profile is symmetrical or not. If I don't hear from TSI I will assume the profile is symmetric and check it the way you mentioned above.

CJD
04-09-2012, 08:32 AM
It's often hard to find the right guy that knows the specs. The sales people are usually pretty useless. You might have to pester them till they give you "the man" that knows!

Good luck,

John

EV2239
04-09-2012, 08:35 AM
The easy way to do it without timing marks is to park cylinders one and six at TDC then rotate the camshaft until the tappets on number six are "on the rock" or one it just about to lift and the other has just dropped. Rotating the cam either way will lift one tappet.

At this position, the lobes on number one cylinder will be pointing downwards because it's the firing stroke. Put the chain on and it will be as near as you can get it, but with a degree plate you can check the valve timing.

To do this measure the exhaust closing/inlet opening first. IE. On the rock or the centre position and write down what you get to compare with the factory spec.

I hope this is clear

Ash

Scott_Hower
04-09-2012, 09:51 AM
It's often hard to find the right guy that knows the specs. The sales people are usually pretty useless. You might have to pester them till they give you "the man" that knows!

Good luck,

John

If Ted Schumacher at TSI doesnt know, then no one knows. :smile:

dklawson
04-09-2012, 09:56 AM
Thanks Ash but the head is not on. I really don't want to put the head on at this point unless I have to . BTW, the method you describe is also described in the factory manual. Watching the rockers on #6 just seems like a very subjective way of determining the balance point on the cam.

Thanks John. Ted is the guy at TSI and I doubt anyone knows more about the S2 cam grind than he does. I guess I just need to keep asking him for the complete specs... or put the head on... at least temporarily.

Scott_Hower
04-09-2012, 10:37 AM
I think your method is fine. Might want to double check to see how close you are to 110 at max lift with the cam gear bolted on. I'd do the same thing, measure at .050 in either direction and split the difference to see what degree you have. My cam card says to let the dial indicator drop at least .080 and then come back up to take up any chain slack.

I've read that it's common for many cams to be "off" several degrees relative to the gears (the cam grind is correct, but grind indexed to the attachment points is off).

I'm about to do the exact same procedure (on a 1500), but with a vernier cam gear to correct any error.

EV2239
04-09-2012, 11:09 AM
The head doesn't need to be on. Just a couple of push rods in No. 6 cylinder so you can see the "rock"

I learnt that trick forty five years ago and it's worked perfectly on everything from Manx Nortons (you set the cams on the "rock" at TDC and then measure the result before rotating through 360 degrees to do ignition timing, or on Rolls-Royce 12 cylinder Phantom IIIs where you time up A Bank and B comes out good.

It really is THE way to do it.

Ash

dklawson
04-09-2012, 11:23 AM
I see your point Ash... thanks for pointing that out. The discussion about rocker arms kept me from even thinking about watching the pushrods instead. Thanks.

dklawson
04-09-2012, 08:41 PM
Success !

I tried several different cam sprocket orientations to get the LCA set to 110 degrees and ended up where I started. Then I recorded the angle at 0.005" each side of the max lift point and averaged those angles. Finally I recorded the crank angle when the cam had 0.013" of lift at opening and closing. All my measurements regardless of method resulted in an average angle of 108.5 degrees. For me, that's not just close enough... it's close to where I wanted to be anyway so I left the cam where it was and fit all the locking hardware.

Thanks to all who offered suggestions here!

EV2239
04-10-2012, 05:34 AM
It's not critical on an engine like that and even with highly tuned racing engines with vernier adjustment, you're lucky if you get that close. This is the reason to do it on the "rock" because it averages out the errors.

Ash

Scott_Hower
04-10-2012, 08:06 AM
Good news.

Can I ask what you used for cam lube? Mine came with lube, and I stored it in a safe place. So safe, in fact, that I can't find it!

CJD
04-10-2012, 09:02 AM
Doug,

That's actually perfect, as having the cam advanced ads low end torque (in contrast to high end horsepower), and it allows for some stretch in the chain.

Perfect!

John

dklawson
04-10-2012, 11:15 AM
Good news.
Can I ask what you used for cam lube? Mine came with lube, and I stored it in a safe place. So safe, in fact, that I can't find it!


I have used a couple of products on different engines. This time I asked Hap Waldrop (he is an engine builder who posts more frequently in the MG and Spridgets parts of the board) for his recommendation. He suggested using CRC lube with moly/graphite.
https://cf.mp-cdn.net/eb/e3/df891b019171e848932addf8715d.jpg

This stuff is very different from what I have used in the past. It is thicker (like a very thin grease) and it is clearly "filled" with moly-disulfide and graphite. It really stays in place.

John, thanks for the comments. The stretch factor and low end torque aspects both came to my mind also which is why I didn't fight to get closer to 110 degrees.

Scott_Hower
04-10-2012, 05:16 PM
Good news.
Can I ask what you used for cam lube? Mine came with lube, and I stored it in a safe place. So safe, in fact, that I can't find it!


I have used a couple of products on different engines. This time I asked Hap Waldrop (he is an engine builder who posts more frequently in the MG and Spridgets parts of the board) for his recommendation. He suggested using CRC lube with moly/graphite.
https://cf.mp-cdn.net/eb/e3/df891b019171e848932addf8715d.jpg

This stuff is very different from what I have used in the past. It is thicker (like a very thin grease) and it is clearly "filled" with moly-disulfide and graphite. It really stays in place.

John, thanks for the comments. The stretch factor and low end torque aspects both came to my mind also which is why I didn't fight to get closer to 110 degrees.

Thanks. I'll try that if I can't find the little tub that came with my cam.

I know Hap well, he built the head for my engine. :smile: