Tappet Adjustment

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AustHaflinger
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Tappet Adjustment

Post by AustHaflinger »

I have always had problems with the tappets in my engine closing up. This time last year it was so bad that some of the valves were not completely closing and compression was down on one cylinder.

I reset the tappets 1000km ago to .152mm (that is the closest my feeler gauge is to .15mm) and today I checked them again and there is no gap - not pushing on the valve stem but no gap at all. The locking nuts were all quite tight so they have not loosened. I really do not feel like doing this every 1000km or so.

Does anyone else find that their tappets close up. Is there a way to prevent this noting the locking nuts are always tight - what about thread locker on the adjuster and lock nut?

Cheers

Garry
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kerry460
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Re: Tappet Adjustment

Post by kerry460 »

have you got the big genuine steel washers on the head studs ,
i have seen this with thin washers .

kerry
ex Tasmanian Haflinger agent .
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AustHaflinger
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Re: Tappet Adjustment

Post by AustHaflinger »

I have the big thick washers, 2-3mm thick.

Just as a matter of interest - why would thinner washers make a difference??

Cheers

Garry
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kerry460
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Re: Tappet Adjustment

Post by kerry460 »

thin and or smaller diameter washers can bow /coin and settle into the stud posts .
giving wrong head tension , but this gives loose tappets .

out of interest what tappet clearance do you use .
I will not go on memory , I know I always ran exhaust a bit different to factory .
because they had a habit of tightening ,

I will put up the specs later

kerry
ex Tasmanian Haflinger agent .
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heinkeljb
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Re: Tappet Adjustment

Post by heinkeljb »

If we look at the physics of the valve system, maybe we can work out whats happening to your gap Gary.

The barrel is squashed up to the crank case by the cylinder head. This is done by the 4 long barrel studs. When you use thick washer you spread the load and the washer does not deform very much as you get the torque to the correct amount. IF you use thin washers under the nuts, they could deform over time with the heating and cooling of the cylinders and so get thinner.

Valve gap is dependent the valve stem staying in the same place when closed. This is controlled by the valve face on the valve and the valve seat in the cylinder head and the overall length of the valve. So if the valve seat and valve erodes, which it will over time. Then the relative position of the end of valve stem will move further away from the piston. This erosion can happen very fast if you have a soft valve seat and use unleaded petrol. One of the reasons lead was added to petrol, it slowed this erosion down.

I do not know if the valves and valve seats used by the factory originally were hard or soft, i.e. were they designed to cope with unleaded fuel. I use a lead substitute in Lurch just is case they are soft.

Anyway, to get back to valve gaps; One end of the push rod connects to the Cam the other to a rocker and hence via a screw adjuster to the top of the valve stem.
So the places for wear in these items are the following:-

The connection to the Cam, the connection to the rocker and the screw adjuster. The ends can become "un-hardened", the ends can become loose on the push rod, the push rod is bent and so does not hold its length when the engine tries to compress it when opening the valve. The hardened surface on the rocker has worn off, the tappet adjuster's hardened surface has worn off. The threads in the tappet adjuster are worn on either the tappet adjuster of the rocker arm. The distance also depends on the cylinder head to barrel and barrel to crank case joints. Having gaskets in there that change shape after having had the head torqued down can also change the valve gap.

Now the only issue is where in all these place is the wear happening to make your tappets close up in 1000kms?

My first guess would be the valve seats if you are using unleaded petrol with no additive. Next would be push rod.

A wild guess could also point at the cast mounting towers which hold the rocker pivot pins. They might have cracks at the base - far more likely this would make for inconsistent valve gaps.

I hope you find the culprit and that it is not a pain to cure.

John
Haflinger 703AP LWB 1973 - (Once owned by Lady Sutherland & Sons.) Now called "Lurch" !

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Re: Tappet Adjustment

Post by kerry460 »

I have gone back into my paperwork.
it was common for clearances to close , particularly exhaust .

I always set both at 8 thou .21 mm
if having difficulty setting them accurately , err on the loose side .
set cold

this is 2 thou above recommended , never had problems .

kerry
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AustHaflinger
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Re: Tappet Adjustment

Post by AustHaflinger »

Thanks John - I discussed valve seat recession or erosion with my engine builder when I got new barrels and the heads done a while back. I used to use valve saver in the engine when I got it but the engine builder said that the heads on Haflingers had hardened valve seats (as just about all aluminium heads are) and did not require valve saver. So I have not been using it - I might start using it again as it is cheap insurance just in case he is wrong.

Kerry - thanks for that information - the specified gap is .15mm on both valves when cold but I might reset at your .008" setting and see how it goes - a noisy tappet will mean there is still gap.

Cheers

Garry
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Re: Tappet Adjustment

Post by kerry460 »

I have never noticed any noise from the extra 2 thou and have set an awful lot at that
I cannot ever recall having any problems at that setting , even erring to the loose side of 8 thou

kerry
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AustHaflinger
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Re: Tappet Adjustment

Post by AustHaflinger »

Today I re-torqued the heads and reset the tappets to .008" as you suggested - fired her up and no real extra noise though it is hard to tell on my engine as it has a real clack to it - has been like that since I put new VW barrels and pistons earlier in the year.

All tappets that had previously set at .152mm had closed up so hopefully it will take a while this time - right or wrong I did locktite them just in case they have moved - however there was no evidence they had done so.

Cheers

Garry
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Re: Tappet Adjustment

Post by heinkeljb »

Did your engine builder use some thing like this to find out how hard your valve seats are? https://www.youtube.com/watch?v=i1x-vJ85sBA

I have a Heinkel "bubble car" which uses similar technology (Alloy head) and it had soft metal valve seats which eroded very quickly and became completely "pocketed" in a couple of thousand miles. I ended up getting them replaced with modern valve seat designed for unleaded petrol.

If I ever have to get head work done, I will have the valve seats machined out and replaced with suitable valve seat and buy suitable valves to go with them.

John
Haflinger 703AP LWB 1973 - (Once owned by Lady Sutherland & Sons.) Now called "Lurch" !

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AustHaflinger
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Re: Tappet Adjustment

Post by AustHaflinger »

I doubt that they did any testing as such and simply relied on their experience on these matters - they have been in the business for about 50 years.

However given the low cost of valve saver (I carry it under the seat next to the tank filler) I will start using it again.

Cheers

Garry
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AustHaflinger
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Re: Tappet Adjustment

Post by AustHaflinger »

Just be aware that the Handbook has tappet gap at .2mm but the Workshop Manual has the gap at .15mm :?

I have gone as high as .24 without any real issue and to go on the high side may be an idea as the tappets do tend to close up.

Garry
Haflinger 700AP (73)
Range Rover Sport TDV6 (07)
Landrover FC 101 (77)
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