Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: billy192 on September 12, 2014, 06:55:23 PM
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Well, just got used to having oil droplets now and then on the outside finns went out for a ride and POP out blowes NO1 plug. got home on 3 and replaced with new plug but will not nip up v tight. it tightens but not as much as it should. got a feeling it will pop out again.
if it does then can you get helicoils to fit? if so what size would i need please? it seems just as you start enjoying the bike BOOOOM another issue. i suppose its engine out head off as a minimum.
happy bloody days
Billy
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Nope, you can not helicoil one. You need a insert to do the job.
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Billy
Many moons ago I have done helicoils on the plugs without taking the head off but never on the fours.Twins you can get away with it but fours I really would not take the chance.F ing bummer I know sorry mate you have to do it all again
Cheers
Bitsa
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Nope, you cannot helicoil one . . .
Why not?
A Helicoil is an insert anyway, or are you thinking of the more 'solid' machined inserts?
(http://www.acmeindustrial.com/images/treads.jpg)
No reason it couldn't be fitted with a Helicoil, as long as there is enough good metal left once you've drilled out the damaged threads.
Could possibly be done in-situ, but you'd need to rig up some sort of drilling attachment to ensure you drilled the hole perfectly in-line with the original.
Much better to do it with the head off though, using a Milling machine, or a good pillar drill at the very least.
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I have used heli coil lots of times but not for spark plug hole. i can't see why not
billy
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Nope, you can not helicoil one. You need a insert to do the job.
Guys listen to the man, he knows what he's talking about...
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Helicoils are only good for blind holes. For a non-blind hole your need solid insert. The helicoil will do the job but, what i have found is when you next remove the spark plug the helicoil will come out with it. Then you will have to get a solid insert. Better to do the job right the first time ;)
If you have anyone local that reconditions cylinder heads, they will be able to do the job.
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Trig
Have to take your word for that but I have to say dont remember that happening back in the 70s.Bryan do you?
Cheers
Bitsa
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Bitsa, the best thing with using a solid insert is you can put it in with a little retainer. You can't use retainer on a helicoil.
1970 Bitsa? I thought back then you just wrapped a bit of tin foil round the thread and squeezed it back in.
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Trig
Fair enough mate as I did not keep up with technology of today all I can remember is back then.Can you update me with photos to my email address as I am curious to see this?
Cheers
Bitsa
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My understanding was that use of a Helicoil (stainless steel) in an alloy head was a bad idea, for spark plug holes because of the different material properties (coefficient of thermal expansion), especially in high temperature variance areas (i.e near the combustion chamber). Probably why the stainless inserts lose grip over time in the alloy head?
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Trig
Naw mate tin foil was used on fuses.Just kidding but you would not believe how many I have seen like that and also frac fuses just strip the ends and twist them together
Cheers
Bitsa
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James, you want to try and get the stainless steel spokes out of a wheel when they have used alloy nipples. That is when its time for the bolt croppers.
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Trig
You are a wealth of info all i can say is hmmmmmmmmmmm forgot about that
Cheers
Bitsa
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Bitsa, you did not order stainless steel spokes with alloy or stainless nipples? The best is nickle plated brass for stainless ;)
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Trig
Not ordered anything yet but will take in to what you have said thanks mate.DS setup then is what he seems to be the cheapest with this.
Cheers
Bitsa
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Timesert apparently, something like a helicoil but it grips the head better, according to a mechanic neighbour. Personally I dislike helicoils where they will be regularly disturbed, I have found they can both go in further which on a cylinder head would be a bit of a disaster, or come out with the fastner (or plug I geuss) which gets to be a pain what with replacing the insert every time theycome out and distort. Handy things but they have limitations.
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Yes you can helicoil it as they do make the kit for the plugs, yes you can do it in situ if you are VERY careful and methodical, yes they can cause problems and come out with the plug if everything is not done correct and lubed right.
Did many a CB/CD 175/250 twin way back when in situ and only ever had one problem BUT always gave the customer the option and explained ALL the pro's and cons. The fours seemed to be looked after better and didn't loose threads as often also the solid inserts wern't about then, or at leasr not as easy to come by
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When I was at school and the Brit bike guys were regularly Helicoiling their Triumph/Enfield plug threads ::), there was a school of thought that the Helicoil created a slight drop in thermal conductivity between the plug and the head but as Bryan says, inserts were not about then and I am not sure what diffrence it would make. Use a slightly hotter plug? Or maybe it's just Bol**cks. The same guys used to listen to Frank Zappa and the Incredible String Band for gods sake :D!
Cheers ...AshD
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Or maybe it's just Bol**cs. The same guys used to listen to Frank Zappa and the Incredible String Band for gods sake :D!
Cheers ...AshD
(http://www.tiptopglobe.com/skin/smile/s10745.gif)
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Nephew has a Ford F150 Harley with the V8 supercharged motor and the early ones had a habit of blowing plugs out as there are only 3 threads on a short reach taper seat plug. There is an insert system available in the US that uses anodised alloy inserts held by locktite and a steel pin. This is the only one that Ford recognise as a suitable repair due to the heat transfer problems with the state of the motor tune but there is a vast difference between a new highly tuned motor needing high octane fuel and a 40 year old "cooking" design that will run on 2 star unleaded
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You can helicoil the spark plug hole, but never in situ, the swarf from drilling, and the tab from the helicoil would go straight into the head, and you do not want that, also as advised, you need to make sure that the drilling is in line with the existing hole or this would also affect the engine running (combustion chamber) after completion. also as advised, solid insert is much better (I would take off the head and send to the engineer's shop, then its done right)!
Sorry for the advise as you were doing so well, and the bike is great.
John
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(I would take off the head and send to the engineer's shop, then its done right)!
[/quote]
I would also take it to a engineer shop and ask them to put a solid insert in but, that is just me.
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I have done lots "in situ" with a well greased drill, turned by hand; a well gresed tap used slowly and great care with the tang--also start the engine with the coiled plug not fitted to blow anything out.
ALWAYS explained the risks to the customer with alternative costs and ony had one failure.
Same as linking camchains, never had one fail but ALWAYS gave great details of cost and risks
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Bryan, I have never had any problems with a linked cam chain but, have seen some horror story's.
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You can helicoil the spark plug hole, but never in situ, the swarf from drilling, and the tab from the helicoil would go straight into the head . . .
A bit of Aluminium swarf will do no harm inside the cylinder, it would most likely be blown out the exhaust before the engine had even fired.
It would be easy enough anyway, to remove the down-pipe for the cylinder, and shove a Vacuum cleaner hose in it's place, suck out any swarf as it's created.
The Helicoil Tang can go the same way, or use Needle-Nose Pliers to remove without dropping.
I agree that a solid insert (preferably with some sort of locking) is preferable.
You already have dissimilar metals involved in every head that exists (unless you either have a Steel head, or Aluminium Spark Plugs ;)), so having a steel insert will be no problem.
Galvanic corrosion needs moisture to form, so it's unlikely to be a major problem in a Spark-plug bore.
It can be virtually eliminated as an issue anyway, with a little Never-Sieze, CopaSlip or similar.
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As the bike was running until recently like this then you could try this as a stop gap.
Yes I know it's a bodge, but you could try running some solder round "tinning" the threads of a new plug and then gently chase out the the threads to make sure there are no lumps in them, it could give you just enough to make the plug bite and give you a serviceable solution.
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I suppose this would already have been done by someone if it were possible/worthwhile, but is it possible to tap a piece of steel tubing with a spark plug thread, then cut an external thread on that piece of tubing and cut a matching thread into the cylinder head, then braze the tube onto the spark plug and screw the plug into the head as normal, so basically you have created a spark plug with an oversize (bigger diameter) thread and then tapped out the cylinder to suit, no insert to come loose cos it's part of the plug, (actually you could turn the threads off the plug and braze an externally threaded bush onto it), it's possibly less work than taking the head off?just a thought!
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Can't see any problem doing that.
Mind you, if you had the tooling and skill to do it, you may as well make an insert to fit in the head permanently.
No need to remove the head for either option either.
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I have done similar with a kh125 to get a dti gauge held securely in the head to accurately determine that tdc was not where it should be according to the timing marks which enabled a cornflakes packett base gaskett to cure a piston eating engine. I rather suspect one could get away with just brasing a close fitting tube to a plug with a thread cut on the outside of the tube, and matching thread in the head, less chance of the insert failing during manufacture, one less tap to buy but every plug change it would need re doing - I reacon it would work, but not how I would gomabout it. To my mind better to remove the head, use a proper insert and have peace of mind, and not just a helicoil, a proper insert that you lock in place mechanically. Don't get me wrong, helicoil are a great thing, just not what I would use for this job. Probably worth saying that it is also a job I would farm out to a pro as A they are better equipped and experienced with full machine shop to back them up, and B in all the years I have run bottom of the market, abused, beat up old hack bikes I have yet to have to do this job so buying the kit even fof a helicoil would be a false economy. So far I have had 1 drain bolt using that thread fail, basically a replacement complete rear end (was a bmw rear drive unit whay did it) from the scrappers was less than a helicoil kit.
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. . . a replacement complete rear end from the scrappers was less than a helicoil kit.
Seriously?
I wouldn't go to that shop again :o
That or you found a seriously cheap breakers 8)
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M12/1.25 helicoil kit don't come cheap. £50 For swing arm, rear drive unit and wheel with good tyre and wheel with rear disk brake. Got a bargin but i was buying in bulk there. Had 5 project bikes. So had £500 worth of stuff. Old school place. Used to be remove it yourself. Sold as seen.