Valve Shim Question

Im shimming my valves.

The clearance is 0

The spec is .16

The current shim is 1.825mm which leaves me with 1.665. So do I go with 14919-MBB-000 .0650in 1.65mm OR

14920-MBB-000 .0659in 1.675mm?

Thanks!

with zero clearance you need to put a thin shim so the valve seats all the way into the seat and then remeasure

do you have a kit?

No kit. Was hoping to avoid the $75 for two $5 shims. Any advice on how thin of a shim?

Be careful. You don't get an accurate measurement of the clearance when the clearance is zero.

You can make an initial adjustment so that you have a non-zero clearance, then re-measure the clearance and change the shim size if necessary.

I would strongly recommend that you just get a shim kit from Hot Cams. It is extremely convenient for just the situation you are in.

Regarding choice of shim size, I like to run one or two thousandths tight. I think it helps keep the clearance from changing.

The problem with zero clearance is it might but less that zero clearance depending on how much the valve has stretched. You will have to go thinner to get some measurable gap and re-measure to get a more accurate measurement. Here is a link to a shim calculator from CRF's Only. The thinnest shim is 1.20mm. Hope this helps.

http://crfsonly.com/calculators/crf450-valve-shim-calc.php

Great thanks for all the help guys. I think I am going to take a shot with the 1.65mm shim and then adjust from there and then get the Hot Cams kit if that doesnt work.

Take the thing apart and see what shims youve already got. Then you can think about what you may want to do.

A refill shim kit gives you 5 shims of each size in .05mm each ( 5 ea. of 1.50, 1.55 etc) IE from say 1.50mm to 1.75mm. So, if you need a couple 165's and a 170, you can get everything for about half of what 1 shim will cost you from the dealer and have a bunch of others you can hang onto. Thats how Ive done several of the 250F's Ive had, since I don't do a lot of them I didn't buy a whole kit. Its a decent handful of shims for the money.

All the 450's use the 9.48mm diameter shims.

http://shop.thumpertalk.com/catalogs/Tucker_Rocky_Offroad_2009/default.asp?p=457

The problem with zero clearance is it might but less that zero clearance depending on how much the valve has stretched.

they don't really stretch it just seats deeper and deeper in the face of the valve and it gets cupped. Once the plating on the valve starts to go it goes quick it's really better to replace the valve before it beats the shit out the valve seat CRF450R019.jpg

they don't really stretch it just seats deeper and deeper in the face of the valve and it gets cupped. Once the plating on the valve starts to go it goes quick it's really better to replace the valve before it beats the shit out the valve seat CRF450R019.jpg

Oakhillbiker hit the nail on the head. It would be wise to start thinking about a head rebuild if you are going to take it apart. Once the coating on the valve wears off, you are just going to be shimming valves until it is impossible. Buy new valves (stainless or titanium), get the seats cut, new valve seals/etc... and get it back together. Some people go with stainless and other people go with titanium. There are plenty of options (Ron Hamp's coated ferrea valves, ferrea, kibblewhite, big bore thumper valves, etc...) Sometimes it is almost cheaper just to pick up a brand new head from www.bigborethumpers.com with stainless valves. If you want, you can do a search regarding intake valves and get mountains of information to make an informed decision.

The valve in the picture isnt that bad really. Whats interesting is the seat. Look at that! Its hammered and chipped up...Thats what a powdered metal seat does for you.

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