Piston to valve clearance with solid cam

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Geoff2
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Re: Piston to valve clearance with solid cam

Post by Geoff2 »

With the clearance that tight, I would check EVERY cyl, not just one. Is it a CamTech cam?
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Re: Piston to valve clearance with solid cam

Post by lc-gtr-1969 »

Yes it’s a Camtech cam, custom grind, but yes, machined by Camtech
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Re: Piston to valve clearance with solid cam

Post by MadBill »

To me it would come down to whether it was an auto or will have a rev limiter. If yes, I'd run it as-is. If not, I'd ponder how likely you are to to wing it to the moon on a missed shift and then decide if you need another mm of insurance.
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Re: Piston to valve clearance with solid cam

Post by F-BIRD'88 »

The copper gasket is going to crush a bit. Take this into consideration. I'd check the exhaust VTP clearance at .028" valve lash. Consider running it as such with this bigger exhaust lash setting HOT.
Can also advance to cam a hair more.
What is the ex VTP clearance if .028" lash is used?
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Re: Piston to valve clearance with solid cam

Post by DCal »

I don't see why you don't just cut the valve reliefs .5mm so you can stop worrying about it. You get to keep your .040 squench and you will be changing the CR in the least way possible and your cam is still installed the way you originally wanted it. Done!!
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Re: Piston to valve clearance with solid cam

Post by af2 »

DCal wrote: Sat Apr 20, 2019 10:32 am I don't see why you don't just cut the valve reliefs .5mm so you can stop worrying about it. You get to keep your .040 squench and you will be changing the CR in the least way possible and your cam is still installed the way you originally wanted it. Done!!
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Re: Piston to valve clearance with solid cam

Post by lc-gtr-1969 »

Thanks again for all the replies.

I have considered cutting .5mm valve reliefs but as the engine is in car (this is not a 'fresh' build, just a new head on a good but older bottom end), so I am not sure where to get the in-head piston cutters in Australia.

Considering it is only .5mm, perhaps I could grab an old valve (current exhaust is 1.5), say a little bigger than current, and epoxy some 80 grit emory cloth to it and then machine a stop with a grub screw for the valve stem, measure the .5mm I need, set the stop, and use a drill to spin the custom cutter in the head? Obviously tape everything up and add grease for good measure around the edges?

I think .5mm should be able to be removed pretty quickly? I might grab an old piston and see how some emory removes the material.

Thanks again, any feedback on the above procedure much appreciated.
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Re: Piston to valve clearance with solid cam

Post by digger »

An old valve the correct oversize and machine face to have cutting teeth. It's actually pretty easy
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Re: Piston to valve clearance with solid cam

Post by lc-gtr-1969 »

Cheers Digger..

I’m using 1.5 exhaust valve.. I have some old intake valves here at 1.63, do you think that is enough radial clearance?
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Re: Piston to valve clearance with solid cam

Post by steve cowan »

LC-
how hard to pull the short block??
i had a LJ XU1 back when i was a kid so i know them pretty good.
the problem i see is you not leaving yourself much room for cam timing changes if so required.
0.100'' PTV on the exhaust ok but thats the minimum for me.intake you can go tight as long as you have control of the spring.
i would really be dubious about trying to do this ''in the car'' as not alot of room when you up against firewall and trying to completely stop debris would be hard to do.
my opinion - pull the engine -flycut pistons correctly-then you can adjust cam timing as you see fit.
my 2 cents :D
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Re: Piston to valve clearance with solid cam

Post by digger »

lc-gtr-1969 wrote: Sat Apr 20, 2019 6:59 pm Cheers Digger..

I’m using 1.5 exhaust valve.. I have some old intake valves here at 1.63, do you think that is enough radial clearance?
typical radial is 0.050-0.060 so yes 1.63 is ok. if you know the size of the pocket you can machine/grind the valve head down to the same diameter as existing pockets if the valve is bigger.

https://rennlist.com/forums/944-turbo-a ... hotos.html
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Re: Piston to valve clearance with solid cam

Post by MadBill »

I used an over-sized intake valve with saw-tooth grooves cut in it and a lathe tool bit brazed to a scrap exhaust valve to correct and deepen the reliefs on my SBC pistons in the car after I angled-milled the heads and added a much bigger cam. Worked a treat...
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Re: Piston to valve clearance with solid cam

Post by Biteme »

My understanding of those long Holden 6 cams is that the rearmost cylinders are often a couple of degrees behind when the engine is running.
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Re: Piston to valve clearance with solid cam

Post by tresi »

Long ago I seen such cutters that resembled a valve with cutter teeth and an adjustable stop in an Isky catalog. This was back in the early 80's when I was in college. People look at me like I'm crazy when I mention them today.
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Re: Piston to valve clearance with solid cam

Post by In-Tech »

They are still around, ISKY and at least this company make them.
https://www.lindytools.com/ihpc

ISKY
http://iskycams.com/shop/index.php?main ... categories

I've never used either. The Lindy one uses different size guide rods depending on valve guide size and says turn with drill. The isky one says use a tap handle and turn by hand, how does it stay centered or do you have to make your own pilot?

Anyway I sort of remembered seeing more than one available.
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