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Post by madmick on Feb 13, 2019 0:57:33 GMT 1
Hi guys,
can anyone tell me what causes the pitting and damage you sometimes see on the dome of the inside of the head?
Thanks in advance,
M.M.
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Post by tacky1 on Feb 13, 2019 1:03:31 GMT 1
Usually the remains of a broken ring or small or big end bearing.
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Post by madmick on Feb 13, 2019 1:09:52 GMT 1
Thanks tacky.
Does this mean it’s worth less if being sold, and can the damage be improved?
M.M.
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Post by tacky1 on Feb 13, 2019 1:27:45 GMT 1
Yep, It can be machined out, Shouldn't make much difference to the selling price, Its an easy fix with someone who know what they are at, also depends on how deep the damage is...
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Post by JonW on Feb 13, 2019 3:10:54 GMT 1
Defo makes a difference to the selling price, the difference between just fitting it or having to sort it out first.
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Post by icarus001 on Feb 13, 2019 3:43:39 GMT 1
Absolutely it makes a difference.
You can't just machine a load of metal out and replace the head, you'll change the combustion area and that can have an effect on the performance, even changing the shape of the combustion area can change how it performs.
So if you machine a lot of material out you need to put it back, or set the bike up to work with the new dimensions.
Polishing out a few marks is one thing, but if it's bad enough that it needs machining then it's an issue, firstly you need someone that actually knows what they're talking about and can actually do the work. Then unless you have someone that can do it all for free, and then set it up for free, then there will be a cost impact to it. The cost depends on how much needs to be done.
It might run with a mullered or badly altered head, but if it's not done properly then it won't run well.
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Post by tacky1 on Feb 13, 2019 5:19:52 GMT 1
I dunno, it wouldnt make a difference to me. I have had butchered heads fixed. As I said, it can be fixed. Plus, 30 odd year old heads should be machined, get a decent reprofile and squish.
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Post by jon on Feb 13, 2019 8:18:47 GMT 1
Out of all the heads I’ve had (maybe 12 or so?) none have needed machining.
OK I have flatted a couple on plate glass, but not machined.
If you do one combustion chamber you need to do the other, and then skim to get the squish back. This probably costs the same or more than an undamaged head, making buying a damaged one to get machined unviable financially.
Jon
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Post by muttsnuts on Feb 13, 2019 9:56:50 GMT 1
if a head is bad enough to need machining and reprofiling then expect to pay around £100 for it doing, resetting the combustion chamber area and the squish is not a 5 min job, plus you need the kit to do it, a damaged head is definitely worth less than a good head that can be fitted straight away
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Post by 4l04ever on Feb 13, 2019 13:32:07 GMT 1
As mutts says, you need to allow approx. £100 to sort the head out if damaged, so a damaged head is probably worth £10 to £30, where a good head is worth £60 to £150 depending on paint/condition etc.
The original profile seems to work very well, so no need to change the profile significantly except to obtain the correct volume/squish.
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Post by madmick on Feb 13, 2019 20:23:37 GMT 1
Thanks 4lo, and the rest of you guys for all your replies.
I am now in the know and fully informed 🧐
M.M.
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Post by reedpete on Feb 13, 2019 20:42:49 GMT 1
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Post by midlifecrisisrd on Feb 13, 2019 21:24:06 GMT 1
Jeez that's bad Expected it to be Jeremy selling that 🤣 Steve |
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Post by bezzer on Feb 13, 2019 22:33:51 GMT 1
To be fair he has put “some detonation” in the description!! 😂
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Post by tacky1 on Feb 13, 2019 22:53:47 GMT 1
To be fair he has put “some detonation” in the description!! 😂 Maybe bombardment should be in there  |
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Post by bezzer on Feb 13, 2019 22:55:15 GMT 1
To be fair he has put “some detonation” in the description!! 😂 Maybe bombardment should be in there Hiroshima stylie!!! 😁 |
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Post by bare on Feb 14, 2019 2:58:43 GMT 1
Cyl heads can Easily be machined to remove Shrapnel damages.. 70 thous is within reason.
Typically the machinist reprofiles the comb chamber /dome and the squish band.
Yess it can be improved and the band angle is cut to match the piston profile IF the machinist is on top of his game.
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Post by icarus001 on Feb 14, 2019 3:22:15 GMT 1
Cyl heads can Easily be machined to remove Shrapnel damages.. 70 thous is within reason. Typically the machinist reprofiles the comb chamber /dome and the squish band. Yess it can be improved and the band angle is cut to match the piston profile IF the machinist is on top of his game. I think we all agree it can be done, but there is certainly a cost to it that I would consider if I had the choice of buying a head with no damage versus one with damage. |
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Post by reggieperrin on Feb 14, 2019 9:26:13 GMT 1
It annoys me when people use this term 'Detonation' for what is obviously damage from metal being mashed into the cylinder head...
It's as if them using this term makes the damage ok...
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Post by urbantangleweed on Feb 14, 2019 9:41:34 GMT 1
Jeez, that's bad! Looks like l/h spark plug thread might have an insert in it?
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Post by tony1964 on Feb 14, 2019 10:11:43 GMT 1
Cyl heads can Easily be machined to remove Shrapnel damages.. 70 thous is within reason. Typically the machinist reprofiles the comb chamber /dome and the squish band. Yess it can be improved and the band angle is cut to match the piston profile IF the machinist is on top of his game. I think we all agree it can be done, but there is certainly a cost to it that I would consider if I had the choice of buying a head with no damage versus one with damage. Stan Stephans machined my head for me last year , cost me £40 |
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Post by madmick on Feb 14, 2019 17:54:55 GMT 1
It annoys me when people use this term 'Detonation' for what is obviously damage from metal being mashed into the cylinder head... It's as if them using this term makes the damage ok... Thats the sentence I was looking for. I was confused with the “DETONATION” term. i was thinking detonation wouldn’t cause this type of damage 🤨 Thanks reggie. M.M. |
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Post by marrcel on Feb 15, 2019 10:19:45 GMT 1
I think Buckshot or clusterbomb is closer😋
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Post by jon on Feb 15, 2019 10:31:20 GMT 1
I think we all agree it can be done, but there is certainly a cost to it that I would consider if I had the choice of buying a head with no damage versus one with damage. Stan Stephans machined my head for me last year , cost me £40 Hi Tony, Was the £40 just for skimming it? To reprofile both domes and skim it is more like the £100 others are quoting in my experience? Jon |
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Post by tony1964 on Feb 15, 2019 10:44:59 GMT 1
Stan Stephans machined my head for me last year , cost me £40 Hi Tony, Was the £40 just for skimming it? To reprofile both domes and skim it is more like the £100 others are quoting in my experience? Jon Hi Jon, he skimmed the head and re-cut the domes. Tony |
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Post by jon on Feb 15, 2019 10:46:31 GMT 1
Hi Tony, Was the £40 just for skimming it? To reprofile both domes and skim it is more like the £100 others are quoting in my experience? Jon Hi Jon, he skimmed the head and re-cut the domes. Tony Blimey, that’s cheap. I have 2 he could do at that price. Jon |
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Post by icarus001 on Feb 15, 2019 13:51:37 GMT 1
Blimey, that’s cheap. I have 2 he could do at that price. Jon I'm surprised at that price too, I think you'd struggle to get any sort of tradesman (let alone a world renowned engineer) to work for £40 an hour - and a head skim + reprofile to match pistons must take longer than that by the time you've done your measurements, got your kit set up and it's all cut, done and repackaged - unless he's doing a boatload of them and has a jig set up so he drops it in with hardly any set up time. I'm open to be told wrong, I'm not a machinist or CNC operator so perhaps a fast machinist could do it quickly?? |
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Post by badger1 on Feb 15, 2019 15:44:31 GMT 1
Bob Farnham converted a 250 head into 350 spec for me last year
£90
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