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Should Tappets spin??????

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nissanite

nissanite

Senior Member
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The opinions that I have been getting are as different as night & day.
My engine builder (who I have tremendous respect for) tells me tappets should rotate in the bores. The tappets should be slightly convex & the cam should have a slight (.00050-.001) variance accross the lobe. Parts suppliers in the UK agree that they should spin but state the offset of the tappet in the bore should cause the spin. One engine part supplier states that he gave up on making them spin & they just go up & down.
Could any of the builders that are on this forum please give their expert opinion & reason for that opinion.
I have spent a Bazillion dollars on this engine & want to limit problems.
After a short 30 minute dyno run revealed no spin.
 
If I told you that they don't spin, how would you propose to insure that yours will not spin? If I told you that they do spin, how would you be sure that yours are spinning when the engine is running?

Why are you even wondering about it. Put the engine together and they will do what they are designed to do.

And yes, they spin. If you look at a set of used tappets, you will generally see a circular wear pattern.

Sam
 
We ran the engine on the dyno & had a rear crank seal leak. After 30 minutes, the lifter showed only a polished spot in one small location. We suspect if left this way they would probably fail over time.
If I was using original parts from Triumph I agree with your comment. This engine has a performance "SPRINT" cam, 89mm bore, Pauter lightwieght rods, Kinsler fuel injection with a Haltech management system. Many of the Triumph vender supplied parts have not been of the quality we expected. Many things had to be re-engineered or machined. I am getting punch-drunk with all of the issues.
Thanks
 
They should spin in their bore but it's not a high speed or even regulated spin. It's doubtful that 30 min of run time will show any kind of spin pattern. It would take hundreds if not thousands of miles driving to notice anything. There is going to be a period of time where parts such as cam and lifters are seating into eachother. Rest assured that as long as nothing is wrong and they move smoothly in their bores they will do what they need to do.
 
Agreed, in a new build they will likely not spin initially until some wear occurs to overcome the friction.
 
It's kinda like the valves - they are supposed to "spin" on the seats as well. But it's over a longer period than 30 minutes.
 
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]they are supposed to "spin" on the seats as well[/QUOTE]

Oldsmobile developed a spring loaded valve spring retainer that acted as an assist to this very theory, back in 1970. It was appropriately called "Positive Valve Rotation" and it actually worked very well.

I agree that it will take a little more time for the wear between the cam and lifters to show a more positive wear or turning pattern. This is why cam lobes are not perfectly flat.
 
Umm - probably "rotate" is a better description than "spin" if we're splitting hairs...
 
Brosky said:
...
I agree that it will take a little more time for the wear between the cam and lifters to show a more positive wear or turning pattern. This is why cam lobes are not perfectly flat.
Click to expand...

American lobes are not perfectly flat, Europeans are flat.

The reason for the difference:
American engines are low rev V8 engines in most cases, while the Europeans are high rev engines.

To force the lifters to rotate properly on V8 engines they invented the taper grind lobes.

European engines only have an offset to rotate lifters and as these engines have a life between 3500 - 6500 rpm they rotate properly too.

Cheers
Chris
 
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