The Cal-look Lounge

Hi,

I am looking for your thoughts and advice please.

I have a new 2332 motor that was run-in on a stuska dyno. I now have about 300 road miles on her and four passes at the dragstrip.

I have 46mm Ti valves as my inlets and 40mm stainless on the exhausts.
Pushrods are Manton HD thickwall.
Rockers are Pauter roller tip.

So my question is what clearances do you guys think I should run on my street / strip motor ????


On my old motor I ran 44 and 38 stainless all round,cro-moly rods ( can't recall make ) and same Pauters and always set clearances stone cold at 0.004 / 0.006 maybe too much clearance ? They certainly were noisy at that.

Let me hear your thoughts on this please .............

Thanks,

Shane.

Set them to zero!
No lash, but you can still spin the pushrod.

As soon as you start to get any heat in to the engine, lash opens up.
Zero lash is perfectly safe.  My street engine has 70k miles on it, it's been at zero lash the whole time since the initial startup.

X2.

Yes, and thats also the reason for all valve train noise you hear everywhere you go. Get rid of the Mantons and find some good alu ones.

Thanks guys for your thoughts and feeback so far.

I don't build motors myself so excuse my ignorance here, but I would have thought when the valve train parts got hot the metal would expand / stretch making any cold gaps set, smaller ?  So setting zero lash cold ( rotating pushrod ) would tighten everything up when hot ?  ??? Or is it a case that when all the parts are hot they are somehow moving away from each other hence increasing the gaps........

The pushrods stay more or lesh the same size due to them being of chromolly.

I'm also looking at good HD aluminium once, should free up some hp dus to a tighter clearence when hot compared to chromolly when hot.

If you are going the Ali route, look at aircooled.net as they are made of much stronger alloy than the other brands. 86B and CB 650 springs are going well with these pushrods. They use normal factory clearances.

ACN get their pushrods from a shop in Oregon, I think they're called Smith brothers or sth alike?

www.pushrods.net

I`m using the 7075 alu billet ones from JPM. No problems, even with K800`s. But no one needs K800`s anyway..

They do if they use a Pauter or Clay Smith cam  :P Just messin´with ya.  But with today´s knowledge we can get by with a lot less with some carefull thinking.
But Zero on the above engine is good.

T

When the pushrods get hot, they do expand.  But so do a lot of other parts.
Al and Mg expand about 2 times as much as steel.  The engine case expands when it gets hot, such that the distance from the centerline of the cam/crank to the deck for the cylinders grows.  The iron cam/lifters/pushrods inside the Mg case also expand, but not as much.
Then there's the cylinders.  Your pushrods will get to a maximum temp of around 100ºC.  The oil flowing through them controls their temp.  The cylinders at the case end may be around the same temp, but at the top end they are much hotter, therefore the cylinders expand more than the pushrods below them.
Finally, you've got the Al heads.  As they heat up, the distance from the top of the cylinder to the rocker block grows.  It grows much more than the length of the pushrod that passes through the head.
The net result is that the rocker shafts move away from the camshaft much more than the growth of the pushrod.

Does anyone check their gaps hot?

I know it would be a bugger to check but leaving the valves on the seat a bit longer would help transfer heat from the valve.
Out of curiosity how much would a 10.5" pushrod stretch over 130 degrees Fahrenheit oil temperature? (200-70=130)
I realize 'it depends' will be the start of any answer as wall thickness and metallurgy of the pushrod will come in to play.

With steel pushrods set to zero lash when cold, you will have more lash than stock when at operating temps.  So you already are leaving the valves on the seats longer.
The pushrod in your example will expand by .23mm.  Wall thickness has nothing to do with it.  Just the length.  An Al pushrod will expand by .44mm.
There's more to it than just lash.  When you use steel pushrods, your total valve lift is in this case, ¼mm less than if you use Al pushrods.  IOW, Al pushrods make more hp!

Let us know what your hot lash is.

I have and it was way to much,over 0.025thou,turbo motor just after a pass and drive back to the pits,I was shocked :o

cheers richie

+1 Richie! I was shocked too

My Manton 0.058" chromoly pushrods go from the cold 0.04 mm  (the smallest feeler gauge) to 0.25 mm while 1/4-mile racing...I broke an adjuster and decided to check the lash one time.