Shortening valve stems on head re-build

[Guest]

I am in need of advice from those regularly involved in engine work.

I have fitted new valves to the 650 head I am rebuilding for my 550. I decided before I fitted the head to the block I would assemble the valves in the head with buckets, shims and camshaft to check if the valve stems needed to be shortened at all to create enough clearance for the shims to fit properly.

So far I have assembled the intake side valves, buckets, shims and camshaft. There are a couple of valves (I have only checked two at this stage) Cyl. 1 & 3 intakes I am only able to get a 2.30 shim in place which allows the buckets on those valves to rotate. Meaning I have clearance there.

My question is: That only leaves three size shims that are able to be used as the valve recedes into the seats (head) over time. Will this be enough or am I going to run out of clearance in a year or two and have to pull the head again?

If popular opinion is that I should take the valves out and have the valve stem ends ground to provide more clearance then how much should I have removed? I know each valve will be different. But in the range of 2.15 to 3.10mm shim sizes, should I aim for around 2.70mm shim size to be fitted after machine work is done?

The main variance here is the amount that has been taken off each valve seat over the life of the head. There are all new valves fitted. All buckets are in perfect condition, and there is no wear on the 650 camshafts that I am using.

Another piece of relevant information is that the camshaft is not from this motor. I have a good set of 550 cams I could use (although they have more duration than the 650 cams) and maybe there base circle might be a bit less giving more clearance. Should I check this out or just shorten the valve stems.

The main issue I am asking is are three shim sizes enough to last for a good many years to come? That would be a total of 0.15mm of wear or the valve receding into the head by that amount.

Sorry for the over explanation, just wanted to make sure I gave enough information.

[Nessism]

I'd shorten the valves, should only cost a couple of bucks each.

[hampshirehog]

I agree with Ed - shorten the stems and aim for around the 2.8 mark (if your machinest takes too much off you can go out to thicker shims of just over 3).

With those seats cut back you'll probably find that your compression has fallen off a bit - it's surprising what difference that little bit of extra space can make. From my experience you won't notice it in performance though.

[Suzuki_Don]

I agree with Ed - shorten the stems and aim for around the 2.8 mark (if your machinest takes too much off you can go out to thicker shims of just over 3).

With those seats cut back you'll probably find that your compression has fallen off a bit - it's surprising what difference that little bit of extra space can make. From my experience you won't notice it in performance though.

Josh the standard compression on this head is 9.4:1 so I won't be too dismayed at losing a bit. And I think 3.10mm is the thickest shim that is available.

[Suzuki_Don]

Another problem I have come up against is how can I turn the camshaft which is mounted in the head which is not on the motor. You would think they would have put a square on the shaft to make it easy for me to turn it wouldn't you. It looks like I will have to remove the camshaft and fit an old camchain to the sprocket and refit the cam and see if I can turn it that way. There's a lot of pressure on them thar springs

[Big T]

As to your original question, I think .5 mm is the max you can grind off the top of the valve stem

Beyond that, the valve keepers may not stay in place

[Suzuki_Don]

OK thanks for that. I guess my machinist will know all about that. I will make sure I take the collets/keepers with me.

After taking some more measurements it looks like only about .006" to .010" will need to be removedfrom each stem. So should not affect things too much. Mind you I need to rotate the camshaft somehow to take the other measurements on the rest valves.

[Don-lo]

To rotate the camshaft, use the 10mm sprocket mount bolts. Make sure you oil the bearing journals first.