Valve clearances opening up

[shynsy]

Hi all,
Is it possible for valve clearances to open up markedly when you retorque the cylinder head? One of my exhaust tappets is much more noise since retorquing and the clearances now seems to be 0.0118-0.013 inch which is too large?
Tim

[promotor]

What did you set the clearance to? Exhausts can be a maximum of 0.011" on the later spec settings and 0.008" on the earlier spec. Appreciate if you've set to the earlier settings then there is now quite a difference to the others.

You'd only need a slight bit of dirt or metal between valve tip / shim / follower to be present when setting clearances to give a false reading and if that has moved from position it would increase the clearance.
Or you could now have a valve not seating fully for whatever reason which could increase the clearance - a bit of carbon or metal on the seat could do it. Or a valve that's bent. A compression check should show issue if the valve isn't seating correctly.

It could be just that the cotters weren't sat in the retainer fully and have now moved slightly.

What shim thickness, follower thickness and cam setup are you using?

[shynsy]

What did you set the clearance to? Exhausts can be a maximum of 0.011" on the later spec settings and 0.008" on the earlier spec. Appreciate if you've set to the earlier settings then there is now quite a difference to the others.

You'd only need a slight bit of dirt or metal between valve tip / shim / follower to be present when setting clearances to give a false reading and if that has moved from position it would increase the clearance.
Or you could now have a valve not seating fully for whatever reason which could increase the clearance - a bit of carbon or metal on the seat could do it. Or a valve that's bent. A compression check should show issue if the valve isn't seating correctly.

It could be just that the cotters weren't sat in the retainer fully and have now moved slightly.

What shim thickness, follower thickness and cam setup are you using?

Engine is new to me so don't know the answers without taking a look. But compression test is a good call. Also have a boroscope to take a look and will check all the clearances..
Tim

[promotor]

What did you set the clearance to? Exhausts can be a maximum of 0.011" on the later spec settings and 0.008" on the earlier spec. Appreciate if you've set to the earlier settings then there is now quite a difference to the others.

You'd only need a slight bit of dirt or metal between valve tip / shim / follower to be present when setting clearances to give a false reading and if that has moved from position it would increase the clearance.
Or you could now have a valve not seating fully for whatever reason which could increase the clearance - a bit of carbon or metal on the seat could do it. Or a valve that's bent. A compression check should show issue if the valve isn't seating correctly.

It could be just that the cotters weren't sat in the retainer fully and have now moved slightly.

What shim thickness, follower thickness and cam setup are you using?

Engine is new to me so don't know the answers without taking a look. But compression test is a good call. Also have a boroscope to take a look and will check all the clearances..
Tim

To clarify my point on cotters: cotters moving shouldn't normally cause issue as the stem tip would still sit at the same height but if they've moved and are causing the shim to bottom-out it could cause issue.

Are you familiar with setting cam clearances?

What method did you use to retorque? Did you check the torque of the headbolts prior to running the engine? Did they all need re-torqueing, or only some?

[shynsy]

Just checked compression. All between. 120 and 125 psi. So seems OK.
Retorqued by my usual method, slacken off a little to break stiction and then tighten up. A couple of bolts needed A 1/4 turn. Some less.
Tim

[promotor]

Just checked compression. All between. 120 and 125 psi. So seems OK.
Retorqued by my usual method, slacken off a little to break stiction and then tighten up. A couple of bolts needed A 1/4 turn. Some less.
Tim

Agree that's the best way to re-torque rather than just seeing if they will move as it's not clear how much friction is at play.

Compression seems a little low but nice and even. It depends on comp ratio, and whether engine is hot or cold with throttles open when doing the test?
What's the history of the engine? How much has it run since being built?

[shynsy]

Engine has around 500 miles on it.. I don't usually worry too much about the absolute pressure figures given variation between guages but matches my 9.25:1 newly built rover V8. Bottom end was refreshed and head rebuilt.
Tim

[Hawksfield]

Hi Shynsy

I think compression values are low. was it hot or cold and did you open the throttles wide open

I recently did a compression test on my engine with around 40k miles from new build, result was 240psi each

I know this is not your principle problem but you need to be aware of it

Good luck

[shynsy]

Cold, throttles open.
Tim

[512BB]

Something very wrong somewhere. I carried out a compession test on one of my cars recently. All pots measured 210 psi on a hot engine with the throttle wide open, which is exactly what I would expect. At least, that is how I read my gauge. This motor has covered 16k miles. 120 psi on a rebuilt engine, not right. I would redo the test with the engine at running temperature and take it from there.

Leslie

[shynsy]

Thanks Leslie,
Not really a priority at the mo. Just wanted to check all the valves are sealing which they are. Engine seemed pretty pockey and no blue smoke. First priority is working out why the clearances have changed and if it is an issue..
Tim

[elanman999]

Having rebuilt my Twink a few times I find that a few of the clearances always change (up or down) within the first 2 to 500 miles. Unless any have closed up a lot I leave it to about 1000 miles and then adjust as needed. I then check them every year (4-5k miles for me) but they often go three years or more between adjustments.
YMMV.
Cheers
John.

[rgh0]

Clearances opening up can be due to the valve stem hammering a dent into the shim if the shim was not hardened or if the shim was ground and the hard facing lost. It may also be caused by the shim cracking if a shim of less than around 70 thou was used.

Normally clearances set on the bench close up a little once the head is bolted down.

If the cam bearings are worn, valve clearances can also move around in unpredictable ways as the cam shaft moves around in the bearings.

cheers
Rohan

[shynsy]

Thanks Rohan,
I'll have a closer look over the next week and get back to you all.
tim

[shynsy]

Ok so have done a more complete and accurate measure of valve clearances. New feelers and engine stone cold.

Exhaust valve clearances are all pretty spot one 0.010". Inlet valves are all at 0.005" appart from one at 0.004"
These are pretty much spot on yes?

So wonder where the tapping noise is coming from.

The "screw driver" stethoscope makes me think it is cam related and I think the periodicity is half engine speed (but need to check) which confirms this. I suppose I could just not be used to the tappet noise of these twinks.

Tim