Ground shim on both sides

[RHODESIA SMITH]

Hello kind Sirs,

Busy re doing my GS850 GX top end following a blow out of a oil leak on the 30+ year old base gasket.

long story short- took the head to a engine machine shop we deal with at work, bloke helped me out a lot and didnt charge me too much, but he doesnt do motorcycle heads,( mostly does truck engines where clearences are measured in Meters and not thou's!). i gave him all the specs and he has done almost everything right except for annoyingly the one shim was ground on both sides.

question is to you guys out there- is this a problem? why i need to know is that it is very difficult to get local bike shops to take one seriously.

(seriously Flyboy - thanks for the list you gave me but I am afriad to say - all so far have been proved to be not interested.)

i am a bot anxious to get my bike going again, but still waiting for my gaskets and others to arrive.

thanks all

 

[tatu]

What size shim do you need, and do you have a way of getting it to you?

 

[Agemax]

what is the problem with the shim? if he is a decent machine shop owner he will have a micrometer to measure the shim thickness and then determine what size shim you need

 

[chuck hahn]

Theres nothing wrong with lapping a shim to reduce its thickness..Now i wouldnt grind any off the edges though.

 

[RHODESIA SMITH]

Thanks all for your very quick wow,

problem is the shim has been ground on both sides and not on the underside as when one usually grind shims. The edges of the shim have not been ground so it fits fine in the bucket.

Is it true that the shim has a hardened surface on both sides and by grinding it takes the surface off hence fitting the ground shim with the ground surface bucket side down?

The measured thickness as it stands is 2.461mm- so to replace it I would require a 2.45mm thik shim.

the valve clearence was 0.05mm so to fit a 2.45mm would make the clearence 0.06- which is still in spec.
If I got a 2.50mm shim I could grind it down by 0.039mm. That would give me a valve clearance of 0.05mm.

As a note I requested all the clearances to be set at 0.05mm when the head was been reworked/ reconditioned as I have heard from a few local riders that that gives about the best performance.

He is a very competant engine rebuilder , but in this case one of his guys slipped up, and there is not really much can be done about it now: I don't want bad blood to develop. ( He is one of those full of nonsence original Italian engineer types and it took a bit of convincing by me to get him to do the job- he chased me out of the shop on the first occasion, but he is a good guy- we do lots of favours for him too so he owed me one).

tatu- Thank you for the offer of the shim , Im in South Africa - so not sure how I could get it and pay for it from you?

If you all think it is ok to use the shim as it is (ground on both sides) - then I will.

 

[tatu]

SA's ok for post, no? PM an address and I'll sick one in a jiffy bag.

 

[RHODESIA SMITH]

Hi tatu,


I may have found a 2.50mm shim, if I dont come right I will take you up on your offer thanks very much.


post is not great- takes approx 4 weeks for a post card- my old Gran in Bolton sends me goodies and half the time it gets nicked. ( but i can't really blame them - its all good stuff like Yorkshire tea, wagon wheels, Theakleston beer ect ect ect!)

 

[tatu]

ok,
Do you not have any mates who are aircrew to Europe? (It becomes next day then )

 

[RHODESIA SMITH]

yes one of my good friends is a pilots at SAA - flys to Heathrow twice a week at the moment.

 

[tatu]

Then you're in like Flyn!

 

[rustybronco]

Flynn... don't wreck the family name! (me mums side)

 

[chuck hahn]

And dont you dare bash my personal hero..LARRY HA HA

 

[2BRacing]

Hi Mr Rhodesia Smith

I would not use a ground down shim due to risk of wear on the non-hardened surface. As you know, the valve clearance spec is 0.03 to 0.08 mm. I, and many others here, prefer to run the clearance on the high side of the spec, and even as high as 0.10 mm. You will have slightly more noise, but you will have peace of mind that the clearances will not be too small when the motor gets really hot in our summers of +35?C.

I for one seriously doubt that you can actually feel any difference in power at a clearance of 0.05 mm compared to eg. 0.08 mm. Just as long as you are within the range 0.03 to 0.08 mm you are good to go, and I really would not try to get exactly 0.05 clearance.

So I would not go grinding any of the shims down. The standard steps of 0.05 mm are adequate to get the clearance within the correct spec. You will often find that you can swop out shims between the different cylinders on your engine to get the correct spec. Then you need only the minimum number of "new" shims to get all your valves correct. If you have ground down any shims, it is not so easy to "swop out" shims anymore, and you have the additional problem to keep record of the exact thickness of the shims, as you have removed the OEM thickness stamped on the shim.

 

[SqDancerLynn1]

I'm not a machinist, Just guessing he lapped both sides to avoid going thru the case hardening of the shim ???

 

[Big T]

Shims need to be "surface ground" which is a different machine

The shim club guy, ghostgs1 aka Ray, has one, custom did a couple of shims for me

 

[chuck hahn]

they are the same temper all the way thru far as i know..you gotta keep them cool when doing the laps to avoid removing the temper..thats why surface grinders have that coolant system..

 

[RHODESIA SMITH]

We do have a proper surface grinder here at work that has the coolant mechanism.

I will see today if I can get the shim.

thanks all for the speedy replies.

 

[chuck hahn]

If youre gonna grind them yourself..or have someone at the shop do it..tell them to only take 1/2 a thousanth at a time and check it after each pass so you can be very very precise as to how much you are removing.

 

[RHODESIA SMITH]

HI ALL,

thanks for the advice and help, It runs and pretty quiet at that!

all the spares i needed arrived on saturday so I have been reassembling since then and last night filled the carbs up and it fired up straight away- all seems good - no oil leaks that i can see- just need to take it out for a ride and make sure.

tatu thanks again for your offer, i came right with a shim- found a second hand one at the corret size.

cheers again all!

 

[tatu]

You're welcome anytime.