750 - Tappet (Valve Clearance) Adjusters - Wear and Flatting

Haggis

Haggis

Hero member
Location
UK
'ello 750 people.

Adjusting my (SF) clearances today and decided to wind out the adjusters and have a look at the working face.

Quite a bit of flatting...

[My adjusters are non-standard and have a flat screw slot in the top].

Is a degree of flatting normal? Are my adjusters soft? Etc?

Naturally the adjuster is dragged across the valve face when in action, so some wear must be expected

I have re-rounded my adjusters by mounting then in t' lathe and dressing the face with some wet and dry.

Obviously flats are shite for adjustment and must be eliminated. Just a slight turn puts the 'edge' of the flat in contact with the valve and will wear quickly.

Thoughts?

Yours, obsessively, as ever, Haggis.

 
Paul,

The commonly used rounded adjusters (Fiat, I think) quickly aquire a flat spot, just too much pressure on a too small surface.  The OE adjusters have a far larger radius, but these also develop a flat spot after a while.

Both types start off with a very small point of contact, the rounded screws quickly develop a small flat, the large-radius type slowly develop a large flat...

Reckon it is more important the valve stem tip isn't damaged, once this happens, side forces on the valve increase dramatically.

piet
 
1- original adjuster
2- reproduction (with slot)
3- Fiat part
I often found damaged valve heads,
where the Fiat parts had been used.

Ernesto
 

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I won't go on about how I solved this problem forever on my SF motors ... using shortened Rotax ball-and-socket type valve adjusters; a job best dome when the head is off and the valves out, so they can be shortened at the tip slightly.

Some will say they aren't reliable but I've done shedloads of km, many at very high speed, some track days on them, sans problem. I've done the mod to at least 4 other motors and others I know have done the same and still no issues. But beware cheap imitations.
 
Thanks for the tips and info guys.

The type I have is type-2 from Ernesto's picture.

I tested them for hardness and they don't seem soft, so maybe the have just been sitting at the same adjustment position for a long time, maybe a bit loose.

I had heard of quick tappet wear and wondered if it was my type, but now see the very rounded type in the picture and can see how it would happen.

Thanks again.  Paul
 
I consider the std tappet system on a par with points - they work fine when adjusted but undergo a gradual decline from that point on until the next readjustment/repair.

Mind you, i rode tens of thousands of km on the std system and the engine always ran beautifully (with a little increase in clatter factor), just that I always observed the wear as the valve tip slowly deteriorated and the tappet surface with it.

Tappety noise can also be excessive side play in the rockers - another job for head off.
 
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