dialing in a used cam

[TVR Beaver]

My 885's done about 4K miles now and I'm just re-timimg it after an engine strip....
When I get number one inlet to the top it reads max lift from 55.5 deg (so 111) to 58 deg (so 116).
It should be set to 111.25 but obviously there is a bit worn off the tip (although I can't see it when looking at the lobe and it all look nice and round)...

I will try another cylinder but if I get the same I guess I should just go for mid point.

Anyone else had this issue?.. .cheers

[chris52]

AFAI your supposed to take a middle reading the same as you do when finding TDC
So if max lift appears at 111deg and starts to drop at 116deg your cam timing would be 113.5deg

Chris
Hopefully the experts will be along soon to confirm this

[chris52]

Just rethinking my previous post and 5 deg does seem a lot. I take it that there are no heads on the engine yet so you wont have anything pushing the lifter back down expept gravity and the DTI, could the lifter be just sticking at the top for a few deg?

Chris

[TVR Beaver]

TDC's another issue... the front pulleys about 1.5 deg out on the clock and 2 if you go from both side to a stop.... I always like going in one direction as thats the way the engine works?.. it's all down to tolerance build up you know

[TVR Beaver]

no.. thats with Alison pushing down on it... looking at my old 435 and thoes lobes look nice also (except the odd one or two).. after a few miles they must start to flat a bit.. and at 4K it could be 10% through its life?
Don't want to get a new one as you have to run them in and as you know, I also need to run in my bearings and pistons... the two precesses to contradict each other a tad

[spend]

The markings on the pulley are probably correct, you cant use a dead stop & half the angle with offset pistons (the motion is not symmetrical), you have to verify with a dti to get to TDC and half the dwell. I've never taking readings that make me believe I can better the pulley markings ~ but suspect many criticize the pulley because they dont allow for the cranked effect that offset pistons have (hence making the dead stop / half the angle method geometrically imperfect).

[carsy]

TVR Beaver said:

When I get number one inlet to the top it reads max lift from 55.5 deg (so 111) to 58 deg (so 116).

I dont understand what your saying here. I think i know what you are getting at though. I would just time it mid way.

ETA. Sorry understand it now John. Think you will just have to go midway or start again with a new cam.

Edited by carsy on Sunday 13th January 19:43

[TVR Beaver]

spend said:

The markings on the pulley are probably correct, you cant use a dead stop & half the angle with offset pistons (the motion is not symmetrical), you have to verify with a dti to get to TDC and half the dwell. I've never taking readings that make me believe I can better the pulley markings ~ but suspect many criticize the pulley because they dont allow for the cranked effect that offset pistons have (hence making the dead stop / half the angle method geometrically imperfect).

Dave.. just re-checked with the DTI and front cover on.. going clockwise with the crank it does appear to be getting to TDC 1 deg early on the piston or 1 deg late on the pulley markings.. will have a look for play in keys etc... (BTW this is the new pulley and damper I'm on about.. may be worth trying the old one )

[TVR Beaver]

carsy said:

I dont understand what your saying here. I think i know what you are getting at though. I would just time it mid way.

ETA. Sorry understand it now John. Think you will just have to go midway or start again with a new cam.

Edited by carsy on Sunday 13th January 19:43

TBH I think any cam thats been in for 4K would be like this.. I measured the lobes when it was out and they are all within 0.02mm.. it did feal to be getting a bit better on the torque... so if it was set at 111.25 initialy is it going the right way for more torque being at lets say 113.5 deg now?

[spend]

TBH if you want to be exact about TDC, centre of keyway pointing at the bore centre-line on the heads is just about as accurate as you can get IIRC.

You need to make a ring to slot on the pulley or crank with a 180deg thin slot for a @18" straight pointer (so you can accurately point to the top of the heads, then a line across the middle of the bore. When you've done all that you probably come to realize that the keyway was far more accurate to start with than any of the home dreamt methods Any deviation seen is as likely to be poor block machining or twisting/distortion than crank deformation or poor keyway machining in the crank I reckon.

[TVR Beaver]

I was more thinking keyway in the damper?.. as you say, I'm sure the rest is not that far out....

Anyway.. what do you think of the cam.. 4K and already flatting off a tad?..

and if I did fit a new one... how do you run it in on a fresh built engine....

you just can't win

Edited by TVR Beaver on Sunday 13th January 21:43