Irishrover
Well-Known Member
Look at the problem methodically......the existing thread is fecked for the depth that the bolt takes up.
The hole is drilled and tapped deeper than the bolt length.
The diameter required for a helicoil is slightly larger (Not much) than the original thread.
My feelings for what it's worth, is that you will get away with fitting a helicoil without any problems-just make sure you drill & tap the hole out dead square to the block face-you don't want the bolt going into it on the p*ss.
You are not the first and won't be the last to strip a thread in an ally block !!
If you can work out how many good threads are left in the hole, you may be able to get away with a longer bolt cut down to suit. As a rule of thumb, one and a half times the thread diameter of the bolt is the minimum good thread length needed..i.e. for a M12 bolt you are looking at around 18mm length of good thread.
If you are fitting a helicoil, fit the longest one you can get.
At the end of the day, you have nothing to loose so go for it....I feel confident you will be okay.
Don't forget to put Lock & Seal on the thread of the bolts before fitting.
The hole is drilled and tapped deeper than the bolt length.
The diameter required for a helicoil is slightly larger (Not much) than the original thread.
My feelings for what it's worth, is that you will get away with fitting a helicoil without any problems-just make sure you drill & tap the hole out dead square to the block face-you don't want the bolt going into it on the p*ss.
You are not the first and won't be the last to strip a thread in an ally block !!
If you can work out how many good threads are left in the hole, you may be able to get away with a longer bolt cut down to suit. As a rule of thumb, one and a half times the thread diameter of the bolt is the minimum good thread length needed..i.e. for a M12 bolt you are looking at around 18mm length of good thread.
If you are fitting a helicoil, fit the longest one you can get.
At the end of the day, you have nothing to loose so go for it....I feel confident you will be okay.
Don't forget to put Lock & Seal on the thread of the bolts before fitting.
Irishrover
Well-Known Member
7 turns with a thread pitch of 1,5mm. will give a thread length of 10,5mm which is less than the thread diameter of 12.0mm.
The result to this would be a stripped thread after taking into account the torque required and the tensile strength of, in this case, aluminium alloy.
I, myself would work on a safety margin.
Dr_evil
Banned
I've been working with steel in the workshop
not ally, that was what I was going off thinking it might be the same
Irishrover
Well-Known Member
Thanks guy amazing what reassuring words and a few cans of cider will do I will get on it next weekend I did think at first I was going to have to scrap the block - good to see you are back helping
:behindsofa:
Hi Sandy..ain't been too far away...just been lurkin in the background looking at the same old repeat topics that have been done to death.
However in this case, I hate to see someone pulling their hair out unneccesarily when there is every chance of a relatively easy, cheap and working fix.
I think, from memory, that the head bolts are M12 but I may be wrong-no doubt there will be someone coming out of the woodwork to correct me !!! :violent::hysterically_laughi:hysterically_laughi
Now for the real **** take....I am considering getting a V6 Gaylander....Come on you bastids-Bring it On !!!
:cheer2::5biamwithstupid::lvkiss-106:
jamesmartin
Well-Known Member
arent they 7/16 unc
Irishrover
Well-Known Member
Could very well be but the "Rule of Thumb" still applies whatever the thread diameter.
Usually, coarse threads are used for attachment to either non-ferrous and cast iron.
There are certain exceptions regarding tube threads.
:behindsofa:
Hi Sandy..ain't been too far away...just been lurkin in the background looking at the same old repeat topics that have been done to death.
However in this case, I hate to see someone pulling their hair out unneccesarily when there is every chance of a relatively easy, cheap and working fix.
I think, from memory, that the head bolts are M12 but I may be wrong-no doubt there will be someone coming out of the woodwork to correct me !!! :violent::hysterically_laughi:hysterically_laughi
Now for the real **** take....I am considering getting a V6 Gaylander....Come on you bastids-Bring it On !!!
Now with a Gaylander are we still allowed to speak to you
jamesmartin
Well-Known Member
im not so sure that v8 blocks arent helicoiled to begin with but they do come in various lengths and fitted correctly are stronger than std thread
When I rebuilt my 1975 RR Silver Shadow engine many years ago I found that Rolls had helicoiles on all the threads on the alloy block even exhaust. An explanation in the five volume workshop manual states that a helcoil is stronger!. If its good for them go for it! Please do it right, measure five times drill once.
ps. on an earlier Rolls engine when it came to putting the rocker cover on there was no conventional gasket they used a lenght of silk thread all the way round and crossed over at on end. The machining was that good a length of silk sealed perfectly.
ps. on an earlier Rolls engine when it came to putting the rocker cover on there was no conventional gasket they used a lenght of silk thread all the way round and crossed over at on end. The machining was that good a length of silk sealed perfectly.
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I have helicoiled an engine block before.
I stripped the threads on an old Honda Superdream block whilst re-building it. Not quite the same as a V8 perhaps, but a helicoil was the answer.
I bought a kit that included thread inserts, drill bit, and tap, and two insertion tools. It worked a treat. I had to use an insert and a half (cutting one down to length with side cutters).
It worked for years until some local ****s stole the bike and threw it in the canal because they couldn't start it.
As stopover said Rolls Royce helicoil as a matter of course because they're so much stronger.
Just drill carefully and slowly. The existing hole will make an excellent pilot hole for your drill. I think it'll only be 1mm bigger than the current hole. Use a good quality tap to cut the threads for the insert. Aluminium is so soft you'll cut the new threads for the helicoil insert easy.
I've still got the kit. Let me know what size you need, if it's the same you're more than welcome to borrow it and use the inserts I've got left. I'm only up the road.
I stripped the threads on an old Honda Superdream block whilst re-building it. Not quite the same as a V8 perhaps, but a helicoil was the answer.
I bought a kit that included thread inserts, drill bit, and tap, and two insertion tools. It worked a treat. I had to use an insert and a half (cutting one down to length with side cutters).
It worked for years until some local ****s stole the bike and threw it in the canal because they couldn't start it.
As stopover said Rolls Royce helicoil as a matter of course because they're so much stronger.
Just drill carefully and slowly. The existing hole will make an excellent pilot hole for your drill. I think it'll only be 1mm bigger than the current hole. Use a good quality tap to cut the threads for the insert. Aluminium is so soft you'll cut the new threads for the helicoil insert easy.
I've still got the kit. Let me know what size you need, if it's the same you're more than welcome to borrow it and use the inserts I've got left. I'm only up the road.
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