valve clearances

Post by **jbennett** » Tue Apr 20, 2004 10:22 am

I have just set the valve clearances on my '57 Minor (948cc) to 12 thou right through, as per the hand book I have, and it's really rattly, even after the engine has reached operating temp when you would have thought expansion would quieten it off a bit.
I talked to one guy who had an older MG I think, and his clearances were more like 6 and 4 thou.
Have I set them them to the right gap?
Any advice would be appreciated.

Post by **57traveller** » Tue Apr 20, 2004 10:32 am

Could be that there's a bit of wear on the rocker pad underside the same shape as valve spindle which will not be detected using feeler gauges. Whatever you do don't set them to 4 - 6 thou. chances are the valves will not close properly when hot. Probably better a bit noisy than the risk of burnt valves or seats.
12 thou. is the specified clearance. Was the engine cold?

Post by **Kevin** » Tue Apr 20, 2004 11:55 am

There are 2 ways to copensate for worn rockers, you either need an automatic tappet adjuster that works by closing the gap to zero and then each click on the adjuster is a thou or cut a feeler gauge to half width so that it fits within the rockers worn area, not so accurate but gets the clearance nearer, or you can buy new rockers or have them refaced but the will wear quicker as the surface will be softer than original.

Post by **racer** » Tue Apr 20, 2004 12:56 pm

I've seen those adjusters ,they sound good for worn tappets ! Would that be the SPQR adjuster ? Used to be advertised in Hot Car ! God, I must be old !!

Post by **simmitc** » Tue Apr 20, 2004 1:02 pm

Another cause of rattle is if the rocker cover isn't on properly, or the gasket too thin, so that the rocker gear actuall touches the cover. Rare, but I have seen it.

The adjusters, like Gunsons Clickadjust, sound great, but the threads on the adjusting screws must be perfectly clean. Any resistance will afect the device. I have one car where it works fine, and another where there is a different click count for every valve! It's rare for gear to be quite so worn that you can't use a feeler gauge to get it close enough.

Post by **Cam** » Tue Apr 20, 2004 1:50 pm

Also you have to be aware of what rocker ratio they are set up for as they adjust the 'other end' of the actual rocker clearance. I would imagine they are set up for standard 1.2 / 1.3 ratio, but if 1.5, 1.7 or 1.1 ratio rockers are used (other cars) then they might 'read' wrong. Not something we have to worry about as in the Frost catalogue they are shown being used on an A-series!

Post by **Kevin** » Tue Apr 20, 2004 6:10 pm

Would that be the SPQR adjuster ?

Thats the one in my toolbox racer and I remember it being advertised in Triple C (hey who pinched the zimmer)

Post by **Willie** » Tue Apr 20, 2004 6:24 pm

I have advocated using a 12 thou" feeler blade which has been
cut down to be narrower than the width of the valve before, and
it is useful but, if you are having trouble with noisy 'tappets'
it is perfectly possible to check the clearances with the engine
ticking over! Sometimes this is the only way to identify which
rocker is giving the clatter,the moment you insert the feeler
gauge in the offending item the noise will disappear. The only
drawback is that there is a slight oil spatter with the rocker
cover off, and the car should be on level ground.

Post by **Kevin** » Tue Apr 20, 2004 6:30 pm

it is perfectly possible to check the clearances with the engine
ticking over! Sometimes this is the only way to identify which
rocker is giving the clatter,

Quite right Willie I remember a mechanic in the late sixties telling me about that method.

Post by **brixtonmorris** » Tue Apr 20, 2004 7:17 pm

my way of setting gap uses the pitch of the thread to give the gap.
tightern the tappet unitll it makes contact with the valve.
dont apply pressure only contact. but eliminate any play on rocker shaft
then rotate the screwdriver back about a 1/4 of a turn, and do up the lock nut.
1/4 of a turn, may be a little more, is approx 12 thou.
anyone good a maths can work out the correct amount of turn.
this method eliminates any wear in system.
on most minors if you use fealer gauges your gap will be large if you have wear on valve or rocker face.

Post by **winger300** » Tue Apr 20, 2004 9:39 pm

you can identify the offending tappet by holding a screwdriver to the rocker cover when the engine is running, cup your ear over the end and you can hear which is the loudest.

Post by **jbennett** » Wed Apr 21, 2004 1:44 am

I adjusted them while they were cold and there's no contact with the rocker cover. If there is wear on the rocker pad etc, could the tolerance be moved down to 10 thou for instance, to quieten things without causing problems?

Post by **57traveller** » Wed Apr 21, 2004 9:06 am

I've also had rattles caused by badly worn rocker bushes and/or shaft. In one instance the wear was so bad as to cause the the force opening a valve to act at an angle and thus wear the guide oval.
Another way to find the offending clearance(s) is to push down on each rocker at the valve stem end with a suitable piece of wood (NOT your finger) with the rocker cover removed and the engine running. Once again there will be a bit of splatter.
Have used Brixton's method on larger marine engines where for example, making sure it turns with the adjuster, 2 1/2 flats of the locking nut = 1mm. Compensates for wear etc. a treat.

Post by **Cam** » Wed Apr 21, 2004 11:16 am

If there is wear on the rocker pad etc, could the tolerance be moved down to 10 thou for instance, to quieten things without causing problems?

That would be compensating for the worn section on the rocker. If you could accurately measure the worn section to get it's depth and then take that figure from 15 thou then yes you would come up with the correct clearance to the unworn bit but it's a lot of hassle and not worth doing really. Best to use one of the other methods as described above.

Besides which, rattly tappets are a lot more healthy than over-adjusted and quiet ones, as in that case the valves will not be seated properly and will be prone to burning around the edges. If you just pluck a figure from the air and adjust them to that then you do run the risk of the rockers being over adjusted.

I like the idea of calculating the number of turns of the adjuster to get 15 thou. It's a really good one. Anyone have the info (turns per inch) of the rocker aduster?

Post by **57traveller** » Wed Apr 21, 2004 12:42 pm

I'll see if i can find the old rocker gear that came off my Traveller'engine. It's only

a matter of then measuring the thread pitch (TPI), assuming they're all the same thread. UNF? and taking it from there. If anyone else wants to have a go then feel free then we can start a debate on which number of part turns is correct

Brixton reckons about 1/4 turn for 12 thou.
Following on from Brixton's post it's usually a good idea to hold the rocker against the valve spindle (no force) and screw down the adjuster by hand until it just touches the top of the pushrod, that could be impossible though if the adjuster threads are tight.

Post by **brixtonmorris** » Wed Apr 21, 2004 9:11 pm

loosen them.

Post by **57traveller** » Thu Apr 22, 2004 8:58 am

Hardly worth getting out tap and die to to that even if you can get one the right size.

Post by **rayofleamington** » Thu Apr 22, 2004 1:03 pm

if the adjuster threads are tight.

often they free up if you run them back and forwards a dozen-or-so times. If not then yes, doing it by partial turn will be a bit unreliable.