valve clearence v shim sizes

[marshy]

I think I may have a problem. Inlet valve clearances have closed up. In 2 cases I can't get a 0.05mm feeler gauge in and the rest are down to 0.1mm. Am I right in thinking that to increase the gap to recommended 0.15-0.2mm I need to have a smaller shim? In which I don't think I can get a shim small enough as current ones are around 0.1mm (I need a shim the size of 0.05mm which I don't think are available). Am I being thick here or do I have a major problem here? Bike has done 43,000 miles. Many thanks.

[Con Rod]

Yes you are correct in that if the clearance you have measured is less than the recommended range you need to use a thinner shim to get the clearance into that range.

Having the inlet valve clearances close up significantly is not unusual on 1996 bikes. It is however unusual for them to close up by as much as you say. It is very unusual for the exhaust valves to close up by that much.

To put it in context the factory inlet shims would have been about 1.8mm thick. If you are now looking shims less than 1.0mm that means your clearance have closed by about 1.0mm which is a lot and certainly suggests that new valves may be in order.

What does not tally up is that mileage, which is not that high.

Are you sure that your clearance measurements are correct?

If they are then I would recommend taking the head off and most likely replacing the inlet valves.

[marshy]

Brilliant - many thanks for your reply. This does confirm my fears. However, as you suggest I will double check clearances and SHIM size I already have. The shim sizes I have appear suspect as I don't believe you can buy them at this size (1.0mm) and I did measure them on a micrometre. If I go down the new valve route do I assume that they would need to be 'ground-in' to the valve seats? Thanks again.

[TRX 850 #87]

IF you have such a small clearance it is possible for the valve head to have "mushroomed" or the valve seat to have burnt/worn.

Valve mushrooming is usually caused by poor valve material combined with high temps and lots of revs.

Valve seats can burn thru poor grade petrol ie: not enough "lead" alternative in the fuel, or again poor quality material. Most modern valve seats are made from a suitable material that can be used with unleaded fuel and will resist burning, but this doesn't always work.

Standard Yamaha shims are available in sizes 120 through to 240, which means they are from 1.2mm to 2.4mm thick when measured with a micrometer. From the factory your engine will have been assembled such that it would have had shims in the middle of the available range fitted, or roughly 170/180 and this has been my experience on all brands of Japanese motorcycles from new, I find that I am always looking for 165 to 185 shims when I do a service. If you have measured the current shims at only 1mm thickness I would be very surprised as this size is not available from Yamaha and would be unlikely to be offered by an aftermarket supplier because such a size is well outside the norm.

Double check your measurement of the shim thickness (it should be laser etched on the shim) before you start pulling off the head. If the measurement is correct, then yu are looking at a cylinder head service. Yes new valves need to be lapped to their respective seats and this is best done by a professional. Inspection of the old valves will indicate the most likely cause of the problem, but always use the manual and check specs for valve seat size and valve head/stem length before just throwing a new set of valves into it and banging it all back together again.

[Con Rod]

I did this work recently,

Thread here:

viewtopic.php?f=6&t=7414&start=165

[marshy]

Putting cam shaft back on - torque issue.
I have just completed checking and changing shims for valve clearances. When putting the front (exhaust) camshaft back on I have found that if I torque the outlet cam CAMSHAFT CAP bolts to the required Torque (10nm) the free movement of the camshaft is very stiff - if I back-off slightly they become more free again. Is this normal? Have I tightened them too much? Am I being paranoid? Thanks.

[SDN]

Question - have you changed anything?

Is the camshaft running in a different head or vice versa? have you "cleaned up" the mating faces with emery cloth or similar - does the camshaft show signs of 'picking up'.

If the camshaft has picked up and shows signs of scoring try polishing the camshaft bearing with some fine emmery strip

If the answer to these questions is no, strip it all down, clean everything very carefull and reasssemble with oil, carefully torque down evenly and try. If it is still tight you can cut a piece of dowell which is slightly loose in the bearing, wrap some fine wet and dry round the dowell and carefully polish both sides of the bearing until you can torque it down and it turns freely. Make sure you clean all traces of abrasive from the aluminium bearing and lubricate with copius amounts of oil.

I had this problem with a spare set of cams, which had been re-profiled by Kent and got them turning nicely - good luck

[Excalibre]

Putting cam shaft back on - torque issue.
I have just completed checking and changing shims for valve clearances. When putting the front (exhaust) camshaft back on I have found that if I torque the outlet cam CAMSHAFT CAP bolts to the required Torque (10nm) the free movement of the camshaft is very stiff - if I back-off slightly they become more free again. Is this normal? Have I tightened them too much? Am I being paranoid? Thanks.

A couple of possibilities:
Is it possible that the camshaft caps have been mixed up? I can't recall if this is actually possible on the TRX but they are machined as a set with the head and need to go back in the same position otherwise there may be clearance issues.

Are you using and an appropriately sized torque wrench? i.e. a small one that measures in inch pounds (not foot pounds). A larger torque wrench will not be accurate at the extreme lower end of it's scale and you may be torquing it tighter than you think. Also, they need to be torqued down evenly and incrementally to ensure correct alignment.

Lastly, did you oil the bearing surfaces prior to assembly?

[cobbadiggabuddyblooo]

The cam caps will only fit on the corresponding position so can not be mixed. But your correct about not mixing caps from a different head.
I had a similar clearance issue as Simon and had to lightly polish the surfaces to get a nice free feel after 1,000km.
I think Robert in the Netherlands had to do the same when he changed his cams.

Oddly enough when you read the manual when servicing and setting valve clearances.
They ask you to remove the caps in a cross cross pattern from outside working in but on the rebuild of the motor section they state the opposite upon removal..

So the main thing is a Chris cross pattern when tightening and loosening... Working either way from inside out or outside in and done in stages. ( ie. 4Nm then 7 then 10 )
A good quality calibrated torque wrench is essential and make sure your leverage factor ( where you place your hand on the handle) is correct.

[marshy]

cobbadiggabuddyblooo, excalibre and SDN,

Many many thanks for your replies. I do think my torque wrench is not subtle enough and may be over-tightening.
I will also follow-up all your comments.
Kind Regards,
Marshy