Topic: Shims under bucket - how to do valve clearances on a CBR250R???

[lordmoonpie]

CBR250R MC19 valve clearances
I'm putting together an engine from spare parts and have got as far as the cams. Everything is standard CBR250 (RJ) MC19. The only shims I have for the valve buckets are about 192-200s. When I install the cams and check valve clearance I can't get any feeler under any cam lobe.

I assume that as the engine gets older , the shims get bigger - i.e. 200+ so can I work out what shims I need by taking them out and checking the clearances with no shims at all in the buckets? Has anyone experience of doing shim under bucket measuring when you have no idea what the original shims should be sized at? I figure that as I have zero clearance with the 192-200 shims I need to go much thinner - I can go all the way down to 120. Any thoughts?
 
Also, when I have no cams in the head the engine spins over almost with your fingers. As soon as I bolt a cam in, it's almost impossible to turn even with one cam - could this be related to the valve clearances or could it be due to the fact that some of the dowels in the cam retainers are not perfectly cylindrical?
 
Grateful for any help...thanks

[KB02]

If you have zero clearance on the cams, the hard turning is most certainly due to this when the cam is in.

As for measuring for what shim size you need, take the shims completely out. Measure the clearance without any shims. Then measure the cup depth that the shims fit in. Add the two together and subtract your desired clearance and you have a good starting point.

That's what I would do anyway.

[simon#42]

KB02's method should work fine but it does depend upon what the underside of the bucket is like [ some are not flat ] 
simon to be on the safe side i would take one of your shims to an engineering shop and have it ground down to use for measuring . failing that buy one of the smallest shim they make for that model and use that

[Sam Green Racing]

I thought you had binned this project.

[simon#42]

that would be a good idea , spending a small fortune making a replica that is nothing like the original is odd , even for simon !
 

[Sam Green Racing]

Simon is odd, but in a nice kinda way.

No more cheap decals for Sam. 

Sam.

[Killer Canary]

What's a CBR250?

[Sam Green Racing]

http://www.google.co.uk/search?tbm=isch&hl=en&source=hp&biw=1120&bih=701&q=honda+cbr250&gbv=2&oq=honda+cbr250&aq=f&aqi=g10&aql=&gs_l=img.3..0l10.1943.13950.0.22092.12.10.0.2.2.0.440.2454.0j4j4j1j1.10.0...0.0.UEoK3G_1SI0#hl=en&gbv=2&tbm=isch&sa=1&q=honda+cbr250rr+fireblade&oq=honda+cbr250rr&aq=1&aqi=g10&aql=&gs_l=img.1.1.0l10.46287.46637.0.52075.2.2.0.0.0.0.381.701.3-2.2.0...0.0.yHRAsa52VHY&bav=on.2,or.r_gc.r_pw.,cf.osb&fp=2b11a277515da907&biw=1120&bih=701

[Killer Canary]

That's a 250? I'd love to even see one of those!

[lordmoonpie]

OK - Thanks Simon and Sam  - if anyone knows, you two know I AM odd and I'm proud of it
CBR250R engine sorted! I since found that doing shim under bucket valve clearances is really really easy IF.....
....you don't have the inlet cam one tooth out on the cam gear DOH!

The cams are funny things - as they mesh with the gears there is a spring loaded part to the cam gear and as I tightened the cam holders, it lined the scribed line
up with the cases. Turns out that I needed to ignore the closed position and have the line dead  level BEFORE I tighten the holders .

Anyway, all is good and the engine landed in LA today on its way to a new home and an RC163 replica builder who wants a replica that doesn't look like the real thing (Thanks Simon :-))
I now have some pennies burning a hole in my pocket and an old desire to take a Ducati twin and make a single....strange? Me??  

[simon#42]

if your going to make a supermono then i think thats a fine idea , i am however just as odd as you !

[lordmoonpie]

Yeah it will be a supermono Simon - not a replica of the factory one of the mid-90s (too expensive to contemplate that) but a more modern appreciation of it maybe? I'm thinking of going the whole hog - frame, swingarm, seat, tank, all non-standard.

Think it must be somthing to do with our names 

[simon#42]

you could be right simon i have just bought a couple of krauser engines , one day i will make something very very silly !