The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: coater87 on 26.04. 2009 14:07
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Hi,
Looking at the head bolt holes on my barrels, someone at one time jammed some odd thread down the hole and made a mash of them- completely gone.
I am not sure a heli-coil repair would hold here. First, can these be fixed properly or am I best off looking for new cylinders? This is a real shame as they are at standard bore.
Lee
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I had a couple of questionable threads on my cylinders. I had helicoil inserts fitted by a local engineering shop and so far they have held (8 years) and I have had the head off 2 or 3 times in that period with no discernible problems.
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Most common helicoil repair used to be the sparkplug hole on alloy heads, if it holds there ( and they do ) should be ok on a couple of head bolts
All the best - Bill
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Guys,
This isnt just one or two, its ALL of them. I have no idea how or why these guys did stuff like this...
Do you still think the heli's will work?
Thanks,
Lee
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why these guys did stuff like this
Maybe had a leaky gasket, tightened up everything extra+++ tight, one thread went bust, then retightened the others to compensate, then...
Since it's in good shape otherwiswe, it's very worth salvaging, bring it to a renowned machine workshop, good chances they will have the solution.
e
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Lee
Just fitted Helicoil type inserts to my barrels. Made sure they were 2 x diameter inserts to suit the length of bolt thresd in hole. Jobs a good 'un. Manufacturers claim repaired thread is stronger than original and I have no reason to doubt it.
Mike
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Sorry Lee did not spot it was all the bolts, would think it would be alright though, if your in doubt take it to a shop and ask, there are other insert available.
All the best - Bill
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Lee,
I'm with manormike on this, a helicoil fitted properly is as good as the original thread.
In the absence of head bolt torque settings, some people will get their longest bar and hang onto it with gritted teeth. Obvious this isn't necessary.
You don't say whether you have a cast iron or alloy head. Personally, [and I know people might disagree with this], if its an alloy head I would use a composite gasket and torque to about 32 ft/lbs. If its a cast head I would use a solid copper gasket and torque it to 36 ft/lbs. either way, your helicoils will be fine.
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Thanks for the help guys,
I am just looking over the pile of bits I have, and this looks like it will be a common problem. The kids who tore this down to chopper it used an awful lot of Honda parts, including the bolts....must have been shinier!
I am just trying to get an early idea of what needs doing here, as I have decided to crate the whole mess up and send it to Wes Scott Cycles for a sound going through.
BTW, is there anyone on here who has a lot of A10 parts on E-Bay? I have had a look at the UK site and cannot believe the selection you guys have- sure are lucky. Over here, we have one or two good sellers, then of coarse the Taiwan stuff and the guy from Chicago.
Oh yeah, its an iron head.
Lee
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Lee,
Never Never ever buy anything from the "guy in Chicago"
Go to any Brit site and ask for some one to verify the varasity of Marshal from Chicago but don't hold your breath waiting for some one to have a good word to say.
If all the threads are cactus then I would seriously consider going to the next size larger bolt
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Lee,
Must agree with Trevor. Marshall has a lot of bad press and doing anything with him over the internet or other remote communications is probably a problem. I have purchased a few things from him by rummaging through his shop (I don't know if that still exists) and at swap meets. The point being, all is OK if you are standing there looking at the part you want, making your own judgements and expecting no guarantees.
Richard L.
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I think it would be very hard to go that route unless you wanted to drill the head through to take the oversize bolts (assuming they could be got anyway with, say, 7/16th BSF shanks and the small head required to get spanner clearance on these engines). When I had one stripped thread in the barrel of mine, it was luckily on a hole that could be equipped with a stud, so I made one with a 7/16th BSF thread into the barrel and standard 3/8th diameter up top, to take a one-off deep nut. It was the rear right-hand-side hole behind the plug. The holes in the centre of the engine wouldn't, I think, allow the use of a stud and nut unless the engine were taken out to put the head on, which is taking things a bit far.
And such solutions aren't pretty, however functional! Helicoils offer a better answer, which I'd have adopted had I known they were OK for these sorts of applications at the time. It was the folk here who clarified the suitability of helicoils then; the advice is still good, and I think certainly the best option if the whole lot need sorting out.
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I have used helicoils in barrels and have had no problems whatsoever.
Trev.
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I have nothing against helicoils but as you still have to drill and tap every hole, using bigger bolts just deletes one step.
It is ultimately up to you, but there is always more than one way to skin the proverbial cat.
If you se inserts then try and get a set with the longer inserts as you can cut a too long insert down ( with a Dremil & cut off wheel).
The kits usually come with the short ( 1x diameter) inserts which are really only good in thin alloy.
The longer the insert the less chance of it winding out and don't forget to drive them in 1 full turn below the surface.
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Yes, you do still have to make bigger 'oles - but will oversize BOLTS pass down through the head? And will they do up? They already have undersized heads for their shanks. That seemed to me to be the problem there. And was why I made a stepped stud in the one case I was faced with, over which the head could be lowered. Always several ways to skin the cat, absolutely, I'm all in favour. But I wouldn't want to enlarge all the holes through the cylinder head if that's what it would take. But maybe they're big enough already?
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Let me add my voice to the long chorus of believers in Helicoils. I've saved many a volkswagen case with them and those are under a lot more stress than your A7 will ever be. In fact, I'd say that Helicoils will make your barrel better than new since the steel in the helicoil is much better suited to repeated unscrewing/screwing than the coarse-grained cast iron. Also, since you get to use the original head bolts, you don't end up with some bogus pretty-looking, but soft stainless bolts that will fail.
(Alex, I think you clicked to the wrong topic when you replied regarding helicoils.)
I did some looking on the Emhart (Heli-Coil) and Alcoa (Recoil) websites to see if they showed the allowed maximum torque. It was a bit confusing, because the torque value offered was, I believe, that allowed or required for insertion of the coil. One inteesting thing from the Heli-Coil site was the warning to use anti-sieze when using hardened or stainless bolts in Heli-Coils. I have not previously known of or followed this advice. Of course, it is up to you (in the US south, where I am not, "y'all") to decide if you want to do this.
Richard L.
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Thanks richard...
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Heli coils are made from stainless wire so you should always grease the bolts or they will glue themselves to the insert with very little provication. And this applies triple for plug inserts.
And just one little thing that everyone seems to forget.
A hole with a wire insert is not pressure ( read oil & combustion gasses) tight.
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Heres a thought. If you were to experience difficulty obtaining the correct imperial size thread inserts, You may wish to consider using metric.
3/8" = 9.5mm so you would only have to go up .5mm (20 thou") to be on 10mm.
If you used a 10mm fine thread you could probably find some nice high-tensile cyl head bolts from a modern J****ese bike.
If you used a 10 x 1.0 pitch it is approx the same thread pitch as 26 TPI. ie. cycle thread
If you were to use 10 x 1.25 it is approx equivelent to 20 TPI . ie BSF
If you use M 10 x 1.5 is approx 17TPI which is close to Whitworth or UNC (actually 16TPI)
Mike
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Also, When i was a machine toolmaker apprentice I was taught to grease all nuts and bolts on assembly , regardless of what type of steel they were made from.
And i also learnt that helical thread inserts are not suitable for spark plugs as they are not gas tight. I would fit a bronze threaded bush if the need arose.
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Helicoils are widely used for spark plug holes and, from my own experience and research, appear to work just fine. Starting a fire over this and sending everone to the closest machine shop to have their heads redone with bronze inserts does not feel like the best advice, and may not be your actual intent, but people could think it is.
Additionally, Whitworth and BSF wire coils made by Recoil (an Alcoa company) are readily available from various sources.
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Gotta agree with richard here mainly because 1.) no thread except a tapered thread is oil or gas tight, 2.)sparkplugs seal on the shoulder with a sealing washer. There is, however, a common problem with helicoiled spark plug holes in that helicoils don't work that great in thru holes and tend to unthread themselves. Locking solid inserts seem to work best here.
Just my 2c