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Dialling in cams

MonstaS4

By MonstaS4,
in Engines & Forced Induction

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MonstaS4 Collaborator

MonstaS4

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I'm after some advice on dialling in cams on an RB30DET. Due to the positioning of the belt tensioners, the cams do not line up with the marks on the back plate when at TDC. My guess is they are 5 or so degrees out. It's an R33 head so the VCT gear is adjustable from behind, and i have an adjustable exh. gear.

I've made up a degree wheel which is bolted on the crank, but there dosn't seem to be alot of room on the lifter to place the dial guage on. Is there a trick to this? There's no way a dial guage can sit perpendicular to the lifter as the cam gets in the way. Help!

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Warpspeed Experienced

Warpspeed

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I have been all through this myself. You need to take a bit of time and do it properly, otherwise it's a complete waste of time.

The first thing you need is a decent dial indicator with the little screw in ball in the end, and it must also have enough travel to work over the full valve lift (obviously).

Next get a small flat metal strip, and drill a suitable hole in one end and fit it under the screw in ball on the end of the dial indicator. It should stick out a right-angles, like a foot sticks out from a leg. That way, the projecting metal "foot" can sit on the very edge of the cam follower without the lobe hitting the stem of the dial indicator as it rotates past. Until you have tried this, you will not realise how little room there is.

The last, and most important thing is to make up a very solid mount for the dial indicator. It absolutely MUST be mounted parallel with the axis of the valve stem, otherwise the metal "foot" will slide around on the follower and the readings will be all over the place. I made up a special fixture that bolts on top of the camshaft bearing saddles. It requires a couple of longer bolts, but it is extremely rigid, and mounts the dial gauge exactly true. If you are clever, it can be turned around and used on both inlet cam and exhaust cam.

Another handy little gadget I fabricated from an old spark plug body, is a fixture for very accurately finding TDC. It has a long threaded bolt that hangs down inside the combustion chamber, and it stops the piston coming up at exactly 90 BTDC.

With the degree wheel fitted, the engine can be turned both ways to hit the stop, and it should show exactly 90 BTDC one way, and 90 ATDC the other. If the bolt length is not exact. both readings should still be identical. When they are, remove the spark plug fixture and TDC should be exact on the degree wheel.

If you take the time to set it all up and make some special tools, cams can be dialed in very quickly and accurately. This might be important if you are trying a few different cams and have adjustable pulleys.

A really convenient way to turn the engine over is to place the car in fifth gear and just roll it backwards and forwards. It is the easiest way.

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