74zzz Posted May 6, 2015 Posted May 6, 2015 Hi all What's the consensus on head saver shims? My mechanic said the head has had a lot taken off so put a shim on. Do these effect longevity or increase risk of failure? Quote
44014 Posted May 6, 2015 Posted May 6, 2015 Why not run 98 have it tuned properly and enjoy the extra torque from the high compression? Quote
Moderators PB260Z Posted May 6, 2015 Moderators Posted May 6, 2015 Depends on how much was taken off, and what CR you would have as a result. If the CR is not to high, agree 100% with the previous post by 44014. Quote
74zzz Posted May 6, 2015 Author Posted May 6, 2015 Well that what I am thinking however Jim has built plenty of racing motors so I'm assuming he knows what he's doing.... There is no bottom of the 2 on n42 so I'm guessing a fair amount has been taken off.......? Quote
74zzz Posted May 6, 2015 Author Posted May 6, 2015 Have never seen another unmodified head so don't know how much most was on it originally Quote
Moderators PB260Z Posted May 6, 2015 Moderators Posted May 6, 2015 Well that what I am thinking however Jim has built plenty of racing motors so I'm assuming he knows what he's doing.... There is no bottom of the 2 on n42 so I'm guessing a fair amount has been taken off.......? I'm a little curious, if your mechanic has built plenty of race engines and is recomending a shim, why are you unsure of his advice ? Regardless of that the N42 has a cc of 44.6, measure the cc of yours and you will get an indication of just how much has been removed and the percentage reduction in cc and ultimately the impact on the CR. The link below is thread that discusses the different head cc values. http://www.viczcar.com/forum/index.php?topic=6012.0 Quote
PeterAllen Posted May 6, 2015 Posted May 6, 2015 ... how much most was on it originally 107.9 mm http://www.zcar.com/forum/10-70-83-tech-discussion-forum/78826-milling-head-n42.html Quote
Administrators gav240z Posted May 6, 2015 Administrators Posted May 6, 2015 Sounds like it's been pretty skimmed to remove the 2 at the bottom of the casting. Quote
74zzz Posted May 6, 2015 Author Posted May 6, 2015 I guess I'm curious and a little worried as to why he put one on..... It was a while ago now and I'm now wanting to rebuild bottom end with forged gear but am wondering if this will just increase chances of any issues..... Have no clue about head savers hence my question. My thought was he was concerned about detonation.... And took this precaution..... Quote
dat2kman Posted May 6, 2015 Posted May 6, 2015 Virgin head is 107.9 mm thickness What is yours now? I have seen up to 3mm shaved off, but this requires the alternative to the stock oil plunger tensioner, and removal of the friction causing curved sode guide. You then just leave camtowers direct bolted to head. If it has had around 1mm only ff it, the old engine guys used to do a little mod to the mount holes in the oil tensioner block, and elongate the mount holes in the curved guide. A multi hole cam sprocket, or a vernier adjstable can sprocket will go some way to compensating for the reduced height of head and getting cam timing. If you do need shims, i have some sets. Not a big fan of them! Quote
Cozza Posted May 7, 2015 Posted May 7, 2015 Due to the head being shaved, the distance between cam and crank has reduced and causes excessive slack in the timing chain. The purpose of the cam tower shims is to lift the cam up and away from the crankshaft and in turn tighten the timing chain. One of the side effects is that you are also lifting the cam away from the valves, hence the reason you would need thicker lash pads to get a good contact or "wipe pattern" There are other options to tighten the timing chain as dat2kman has mentioned. I don't know the pros and cons sorry. Hope that helps a bit. Quote
74zzz Posted May 7, 2015 Author Posted May 7, 2015 so on closer inspection and cleaning off some grime i don't think much has been taken at all? dont have a virgin head to compare to though.......opinions? that kameari idler gear would sought out tension wouldnt it? would prefer run higher compression if i could:) it was 10:1 before hand looking at records kept by previous owner Quote
74zzz Posted May 7, 2015 Author Posted May 7, 2015 Due to the head being shaved, the distance between cam and crank has reduced and causes excessive slack in the timing chain. The purpose of the cam tower shims is to lift the cam up and away from the crankshaft and in turn tighten the timing chain. One of the side effects is that you are also lifting the cam away from the valves, hence the reason you would need thicker lash pads to get a good contact or "wipe pattern" There are other options to tighten the timing chain as dat2kman has mentioned. I don't know the pros and cons sorry. Hope that helps a bit. He did destroy a brand new set of rockers and ended up just resurfacing the old ones when the head went back on........... bot sure if this was befrore or after the shim went in though Quote
dat2kman Posted May 7, 2015 Posted May 7, 2015 That head is not shaved terribly much! Do a height measure., if it is at 107 ( ie 0.9 mm off) or so, ot could have the tweak done as I mentioned, Jim M at Stone st, knows how to do this, he did a motor for me many years ago, and did this. Chewing f rocker pads is another issue, but can be related, f wipe is set incorrectly. Use a very high zinc content oil, or at least a couple of bottles of a zinc rich additive. Quote
74zzz Posted May 7, 2015 Author Posted May 7, 2015 Cheers Jason Jim was the mech who put the shims in When I give t to him to set up the new carbs i'll ask him about it. He did it a few years ago so may not remember why it was done will see if he kept any details about it. Quote
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