Forum

[ChrisD]

Hi Guys, Is there a quick route to determining if the cams need shimming and if so how?
The only way I can see is to measure offsets from a straight edge placed over the timing chest - easy if the engine+chest are off the bike but really difficult if it is all still together.
Cheers
ChrisD

[Mark M]

What bike? REgards, Mark

[Gwilly]

Hi Chris, I may be talking from the rear end, as my old pop used to say,

But would it be possible to use modelling clay in a simular way to measuring piston

to valve clearances.

Like i say i may not have a handle on the exact problem here.. cheers gwilly

[Alan R]

Hi guys--------- Hello CHRIS D,....... the phrase "cam shimming" is normally used in conjunction with an Over-Head Cam engine (OHC)and bucket tappets...BUT sometimes hydraulic tappets operated by push rods can have the oil cut-off setting altered via the use of shimming....SO, as MarkM says }--- what bike have you got ???

[Alan R]

Hello again CHRIS D ----------- or maybe you are referring to the amount of LATERAL or SIDE MOVEMENT,( ie "FLOAT")that the camshafts assys. have within the timing chest itself ??

[Jack]

Chris,do you have some spare shims?I just put some extra shims on the shaft
then place the cover in position.You can get an idea that it's not going to
screw up because you will have a gap between the gasket.So it's a matter of removing a shim at a time till the gap closes.At this point you could remove 1 shim and be good,or you could then move the cam out on the shaft and slowly slide the cover back on then remove the cover and see if the cam will tap if you push it in,which will indicate a small gap.Clear as mud .It's really easy.Next you simply repeat the sequence with the other cam,jack.

[ChrisD]

Hi. Stupid of me not to say it is a 1996 500 Classic.
The shims available from our hosts, which come with their performance cams, are 5thou thick. I know that is necessary because the performance cams are 5 thou shorter (along the pinion) than normal cams. But the orginial cams were already very noisy and I still have to fix that.

I could of course "suck it and see" by putting an extra shim. But if that is one too many, I think I could still tighten down the timing chest cover because I imagine it could flex to accommodate such a small amount. Similarly measuring a piece of plasticene or other modelling clay to 5thou is fraught with difficulty - and it probably wouldn't hold a 5thou thickness anyway. And since there is so much resistance in the timing chest from the oil pump and all those gear wheels, I suspect I wouldn't notice extra friction from having 5thou too much shim. The only way I would eventually realise it is if the casing is worn where the shim touches it - but that woudl only be after it been ridden. That's too late.
So is there a way to do it without taking the whole engine off, stripping out the oil pump and most of the idler pinions etc and then testing one cam at a time for excess friction? I suspect not, but live in hope.
ChrisD

[Gwilly]

Sorry Chris didnt realise we were talking such a fine measurement...

Still sticking with my original idea, what about plastigauge? once compressed will retain its
shape to enable measurement against a gauge that comes with it.

I have some in the garage i use for bearing clearances 0.001"- 0.007"

Lasts for years... have a look........ http://plastigauge.co.uk/

I'm thinking dont go too tight, allow for expansion when hot.

Could you remove the oil pump worm nut to save the worm gear getting mullered when fit and refit operations going on... gwilly

[Alan R]

Hi guys---------- Hello CHRIS D....... When I was working at the Army Base Repair depot, and similarly at the Brit. Railways Loco. Maintenance depot, one of the ways open for this sort of measurement ( and here I must admit, this would be for repetitive build then measure operations) ---- would be to make use of a scrap casing and have the machine shop slice part of it away such that measurements might be made etc. The calculated shims and service casing would then be assembled....Could you not find a scrap timing casing and do a similar thing ??----------

[ChrisD]

Gwilly
Plastiguage - what a neat idea. I shall definitely try that. Thanks for the advice. ChrisD