YB head 138.68mm limit. Why?
16-10-2008, 02:55 PM
#41
I`ve seen probably no more than 3 heads this thick or more in the last 8 years....
I`m with Tony on this one,poor modification/repair has far more to do with this problem than overskimming........
Stu, you have just scrapped 70% of Cosworth heads in the world with one post
I`m with Tony on this one,poor modification/repair has far more to do with this problem than overskimming........
Stu, you have just scrapped 70% of Cosworth heads in the world with one post
16-10-2008, 02:59 PM
#43
In which case, i suggest Nightol for a better nights sleep. Karl can be found on 01773 836274.
16-10-2008, 03:03 PM
#47
If the valve seat throat has been extensively enlarged i recommend that you peen or stake the seats after they have been installed as added insurance to prevent them from falling out,
I recommended rolling or peening rather than staking. The reason? Staking creates stress points and potential hot spots.
I recommended rolling or peening rather than staking. The reason? Staking creates stress points and potential hot spots.
16-10-2008, 03:04 PM
#48
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Many thanks, I'm glad it helps. 
Wrong topic maybe? Nothing in those pictures has failed...
Yes, a few things, generally i believe you can actually recess the valve seats further into the head and re-machine to suit. There are complications wit doing so but its cheaper than a new head which is of course, currently priceless due to being made out of unobtainium. Karl Norris used to be the man for this job, not sure if he still gets involved though.
Wrong topic maybe? Nothing in those pictures has failed...
Yes, a few things, generally i believe you can actually recess the valve seats further into the head and re-machine to suit. There are complications wit doing so but its cheaper than a new head which is of course, currently priceless due to being made out of unobtainium. Karl Norris used to be the man for this job, not sure if he still gets involved though.
Are they of the turkish origin??
16-10-2008, 03:34 PM
#51
The indicated area is the best visual indication for a layman to determin that a head is excessively skimmed.
This topics simply aims to illustrate the possible pitfalls of purchasing such a head, or building an engine using one. It may be fine, but equally, it may not, and given the fact that a failure will almost always take the block and pistons with it as a bare minimum, would you take the risk?
Also, there are people out there seling heads in this condition for Ł2 - 3 THOUSAND pounds i believe!
16-10-2008, 03:43 PM
#55
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Forgive my photoshop skills...
The indicated area is the best visual indication for a layman to determin that a head is excessively skimmed.
This topics simply aims to illustrate the possible pitfalls of purchasing such a head, or building an engine using one. It may be fine, but equally, it may not, and given the fact that a failure will almost always take the block and pistons with it as a bare minimum, would you take the risk?
Also, there are people out there seling heads in this condition for Ł2 - 3 THOUSAND pounds i believe!
The indicated area is the best visual indication for a layman to determin that a head is excessively skimmed.
This topics simply aims to illustrate the possible pitfalls of purchasing such a head, or building an engine using one. It may be fine, but equally, it may not, and given the fact that a failure will almost always take the block and pistons with it as a bare minimum, would you take the risk?
Also, there are people out there seling heads in this condition for Ł2 - 3 THOUSAND pounds i believe!
thanks makes sense now.
16-10-2008, 04:56 PM
#57
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Stu,
With overheating of the casting being one of the suspected causes of the failure, might it not be beneficial to not only look at the structural integrity of the head itself, but also the water channels which surround the combustion chambers, correct me if i'm wrong but the YB suffers with 'hot-spotting' in modified format, would it perhaps be beneficial to introduce some addtional bleed off points to highly modified cylinders heads to prevent this occuring and potentially stabilise the temperature of the casting...
Ian
With overheating of the casting being one of the suspected causes of the failure, might it not be beneficial to not only look at the structural integrity of the head itself, but also the water channels which surround the combustion chambers, correct me if i'm wrong but the YB suffers with 'hot-spotting' in modified format, would it perhaps be beneficial to introduce some addtional bleed off points to highly modified cylinders heads to prevent this occuring and potentially stabilise the temperature of the casting...
Ian
16-10-2008, 05:03 PM
#58
i searched for ages for a good head. in the end the best i could find was 138.75mm. how much meterial would normally be taken off from each skim? my old head was well under 138 i just cant believe the price some wankey old heads make on ebay. also stu you didn't mention the brass plug in the head. wasn't this an indicator of 138.6mm?
i just cant believe the price some wankey old heads make on ebay. also stu you didn't mention the brass plug in the head. wasn't this an indicator of 138.6mm?
16-10-2008, 05:03 PM
#59
Stu,
With overheating of the casting being one of the suspected causes of the failure, might it not be beneficial to not only look at the structural integrity of the head itself, but also the water channels which surround the combustion chambers, correct me if i'm wrong but the YB suffers with 'hot-spotting' in modified format, would it perhaps be beneficial to introduce some addtional bleed off points to highly modified cylinders heads to prevent this occuring and potentially stabilise the temperature of the casting...
Ian
With overheating of the casting being one of the suspected causes of the failure, might it not be beneficial to not only look at the structural integrity of the head itself, but also the water channels which surround the combustion chambers, correct me if i'm wrong but the YB suffers with 'hot-spotting' in modified format, would it perhaps be beneficial to introduce some addtional bleed off points to highly modified cylinders heads to prevent this occuring and potentially stabilise the temperature of the casting...
Ian
16-10-2008, 05:08 PM
#60
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i searched for ages for a good head. in the end the best i could find was 138.75mm. how much meterial would normally be taken off from each skim? my old head was well under 138 i just cant believe the price some wankey old heads make on ebay. also stu you didn't mention the brass plug in the head. wasn't this an indicator of 138.6mm?
i just cant believe the price some wankey old heads make on ebay. also stu you didn't mention the brass plug in the head. wasn't this an indicator of 138.6mm?the correct way of measuring head thickness is by using a Vernier.
16-10-2008, 05:46 PM
#66
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It may be a dumb question and I'm no engineer....
But could the head face be built up by welding and then re-skimmed to the correct thickness?????
in anticipation of being shot down........
But could the head face be built up by welding and then re-skimmed to the correct thickness?????
in anticipation of being shot down........
16-10-2008, 06:09 PM
#69
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lol find it funny all those folk out there worrying about there heads below 138.68mm (if it working as it is now don't try fix it leave it alone) i'm so so glad i got my mate to keep back two 4x4 heads that have never been skimmed ever as now they are worth that little extra
but on a lighter note the very head i took off my Graham Goode 4x4 Saph which was 1 of there own heads measured at 138.18mm and ran like that for 40,000 miles with no issues, the head i refitted was 138.62mm and that is still runing with no issues
the previous two 4x4 saph (both stage 3 350bhp) i had both had heads below 138.68mm and guess what had no issues!
The 1 leason i learnt though is i had every head checked and rebuilt by a superb machinist and both heads are now still on engines and running 100%
this is certainly a very interesting read as i know of many cossies running big power with heads below 138.5mm with no issues what so ever
but on a lighter note the very head i took off my Graham Goode 4x4 Saph which was 1 of there own heads measured at 138.18mm and ran like that for 40,000 miles with no issues, the head i refitted was 138.62mm and that is still runing with no issues
the previous two 4x4 saph (both stage 3 350bhp) i had both had heads below 138.68mm and guess what had no issues!
The 1 leason i learnt though is i had every head checked and rebuilt by a superb machinist and both heads are now still on engines and running 100%
this is certainly a very interesting read as i know of many cossies running big power with heads below 138.5mm with no issues what so ever
Last edited by silky16v; 16-10-2008 at 06:21 PM.
16-10-2008, 06:14 PM
#70
This topic isnt really about failure, its about educating people so they can actually identify a head at teh end of its usefull life.
The main two things to consider are:
1) Probability of failure. Your money, your risk.
More importantly:
2) If you are building a big power YB, you will definately be investing Ł1000+ into head porting, valves, platform mods, guides, seats etc. Do you want to do that to a cylinder head that has no skims left in it, even if it doesnt mechanically fail? I know i dont, in fact, i know i wont.
The head in picture 1 was from Karl Norris and a beautifull piece of kit it was too.
The main two things to consider are:
1) Probability of failure. Your money, your risk.
More importantly:
2) If you are building a big power YB, you will definately be investing Ł1000+ into head porting, valves, platform mods, guides, seats etc. Do you want to do that to a cylinder head that has no skims left in it, even if it doesnt mechanically fail? I know i dont, in fact, i know i wont.
The head in picture 1 was from Karl Norris and a beautifull piece of kit it was too.
16-10-2008, 06:19 PM
#71
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This topic isnt really about failure, its about educating people so they can actually identify a head at teh end of its usefull life.
The main two things to consider are:
1) Probability of failure. Your money, your risk.
More importantly:
2) If you are building a big power YB, you will definately be investing Ł1000+ into head porting, valves, platform mods, guides, seats etc. Do you want to do that to a cylinder head that has no skims left in it, even if it doesnt mechanically fail? I know i dont, in fact, i know i wont.
The head in picture 1 was from Karl Norris and a beautifull piece of kit it was too.
The main two things to consider are:
1) Probability of failure. Your money, your risk.
More importantly:
2) If you are building a big power YB, you will definately be investing Ł1000+ into head porting, valves, platform mods, guides, seats etc. Do you want to do that to a cylinder head that has no skims left in it, even if it doesnt mechanically fail? I know i dont, in fact, i know i wont.
The head in picture 1 was from Karl Norris and a beautifull piece of kit it was too.
16-10-2008, 06:28 PM
#72
on that note then Stu what about cossies running upto stage 3+ (400bhp max) that can do so on a standard head would you still apply the same that any head below 138.68mm is simply asking for trouble or could we lets say run it that little lower EG: 138.5mm and it will be perfectly fine???(bearing in mind that the head is in perfect working condition)
The annoying thing is when you pay proper money, and then get something like shown above. The customer informs me he paid WELL in excess of Ł2000 for that head in the pictures and it had done very few miles. Had he know how to quickly check, he could have rejected it on day one before running it, hence my topic trying to educate folk a little.
16-10-2008, 06:42 PM
#73
I would advise customers that beyond 138.5mm i will not warranty the head used at all. Its not financially viable for me to do so due to teh risks involved escalating as heads get thinner and thinner but ive used far thinner with no problems. You pays your money, you takes your risks.
Decent heads are almost extinct nowadays
16-10-2008, 06:43 PM
#75
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I would advise customers that beyond 138.5mm i will not warranty the head used at all. Its not financially viable for me to do so due to teh risks involved escalating as heads get thinner and thinner but ive used far thinner with no problems. You pays your money, you takes your risks.
The annoying thing is when you pay proper money, and then get something like shown above. The customer informs me he paid WELL in excess of Ł2000 for that head in the pictures and it had done very few miles. Had he know how to quickly check, he could have rejected it on day one before running it, hence my topic trying to educate folk a little.
The annoying thing is when you pay proper money, and then get something like shown above. The customer informs me he paid WELL in excess of Ł2000 for that head in the pictures and it had done very few miles. Had he know how to quickly check, he could have rejected it on day one before running it, hence my topic trying to educate folk a little.
ok cool gotta agree paying in the excess of 2k for head work on a head that measures less than 138.2mm is hard to swallow, but we all learn by our mistakes, i know i have luckily on a Vauxhall engine so not quite so expensive, fell sorry for the fella hope that company that has performed the work cough up and at very least refund the cost of the head work
16-10-2008, 07:19 PM
#77
years ago i used to see cosworth yb heads for sale with the thickness included in the spiel of the ad, i also used to see yb heads that had one skim too many advertised as ideal for N/A. so is a well skimmed YB head ok for N/A or is it a quick way of getting a decent shilling for old toot
16-10-2008, 08:48 PM
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