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Im getting my vr4 head serviced and putting in super tech oversized valves 1mm over. If the valves were to hit the pistons by hand cranking a few times is it possible to bend the valves if they were to hit the piston tops. What clearances are we after with valve to pistons?
what does the manufacturer of the parts recommend?
Watch out with super tech valves. Thier intake valves are known to crack and drop into the combustion chamber. Ive seen a couple of motors go down from this. (But not specifically 4Gs) Aswell as all 8 of my supertech intakes pulled from my last motor had hairline cracks visible on every valve. Thankfully none had broken off completly, as when they do, its pretty much gonna ruin your day.
Eek, that is scary - they're supposed to be proper race valves - do you recall which alloy they were made from, or if there may have been any valve float/bounce as that kills valves?
Anyway, back to OP - only way to know is to do a dummy build with some light springs and check clearance by gently pressing them down until contact is felt and checking the available travel with a DTI, from around 10 degrees before TDC to 10 after as sometimes the closest to contact isn't quite at TDC. Alternatively, use the plasticine method - or better yet both as each has weaknesses.
Thank you you sir for the info
It could be valve float? On my engine i was using some entry level upgrade BC springs. And Kelford cams. Running decent boost and used for motorsport.
On one of the engines that actually dropped valves, they were using double springs, and more agressive cams. But basically a street car with a few drag pass's.
One engine did have possible P2V contact due to variable cam timing. So thelat could have done it aswell.
In any case. I wont personally be using supertech valves ever again
Understandable, I did some checking after the last post and there does seem to be an issue - certainly a few years back - so Ferrea or Manley valves may be a safer option. Some failures could be put down to other problems causing the valve failure, but a lot where it seems to be directly related to the valve and/or other ST supplied product.
It's all very well having a 99 or 99.99% of people having no problems but when you are that 0.01 or 1% it is a different story.
There was also mention of some 'tuners' reselling ST under their own brand - like Skunk for Honda - so something to be aware of.
A general guide I use for vale to piston contact is to aim for a minimum of 0.080" or 2 mm. Some engine builders will shoot for a slightly more generous clearance of 0.100" on the exhaust. In my own experience with the 4G63 using a 1mm OS valve shouldn't create any problems unless you're running some pretty serious cams. most of the off the shelf pistons for the 4G63 are pretty generous in their valve pockets and give ample clearance with a mild cam profile. Of course you can never assume and always want to check for yourself. When you're checking the clearance also look at the radial clearance from the outside of the valve to the inside of the valve pocket as this is often overlooked.
Thank you Andre. Is it possible to bend a valve by hand cranking if the valve was to hit the piston.
Absolutely! If your cam timing is out then rotating the engine by hand can definitely bend a valve.
When I did mine not a an EVO I removed most of them and just left 2 valves. One intake and one exhaust valve, so if there was a contact I would just have to by two of them.
Another option is to buy checker springs which are much softer for obvious reasons. Just make sure they don't coil bind and they fit well.
The problem with high lift cams and aggressive spring rates is that you don't know when turning the engine by hand if you have made contact or you are just compressing the valve springs.