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Allan G, Andy Carr, NickL
Total Likes: 8
Original Post (Thread Starter)
#838845 02/02/2021 6:00 AM
by DavidP
When I removed the head from my 71 A65 one head bolt was seriously stretched.
I believe that it's the TS rear bolt, but I might be misremembering.
Any idea on what caused this, just one bolt?
Liked Replies
#838884 Feb 2nd a 05:02 PM
by Ignoramus
MY money would be on it being an aftermarket bolt not made out of high/medium tensile steel ?

compare any markings on the heads of the good bolts to this one and see if they are different, a pic of the head of the stretched one and a good one side by side would be interesting

but you were lucky it didnt bust off inside the thread ...the way it has necked down it was sure close to doing that

by the way the necking is typical of freemachining / mild steel that has passed its yield point in tension

another quick (not definitive ) test is hold the bolts lightly by the head and hit the bolt lightly with another piece of bar high tensile will give a pinging type sound and mild will give a deader almost thud sound ....if the sounds are different you can be 90% sure they are different material
2 members like this
#842779 Mar 14th a 05:10 AM
by DavidP
Originally Posted by DMadigan
Maybe you should have used a solid insert.
That was one of my first questions. They are only available in Unified threads and I'd already spent good money on the BSF bolts.
In any case, all four Recoils are in place. The bolts thread all the way in. I only need to lightly hone the bores and wash up.
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#839058 Feb 4th a 06:45 PM
by Ola
David - I have seen new (after market) head bolts that were very sloppy. I would try a known good bolt before going to any helicoiling.

1 member likes this
#838872 Feb 2nd a 02:52 PM
by Mark Z
Mark Z
If the bolt is indeed stretched, it would be most likely from over-tightening or poor metallurgy.
1 member likes this
#840357 Feb 18th a 02:24 AM
by Ignoramus
Nick L recons :

buy either grade 8 or allen bolts (grade 12 or 14) easily

grade 12 cap screws are excellent material .........very high tensile , but still machine able / tap able , (just) best to power tap the sods though , probably 4140 grade .....i often buy a few realy long cap screws with a short thread as they are a very cost effective way of getting just a few inches of good grade material without having to go to a steel merchant who will want to sell you a 3.6 meter bar minimum!

if you get them with a unf thread, or even metric fine series and tap them to what ever size you need you have made a top of the line thread insert , retap the offending hole using a 2nd cut or taper tap and wind then in as hard as you can the hack them off with a hacksaw , file them flush and you have a forever repair ! done that countless times

oh and by the way .......when tapping high tensiles always go .0,1-.0.2 mm above the drilling size (much more on large diameters ) , depending on pitch and diameter , 80% thread is plenty on that stuff and you wont get so many busted taps
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#842354 Mar 9th a 06:09 AM
by DavidP
Nick, I've found it to be just the opposite, though I've only owned the one A65 and my first Triumph was a T150V.
I can set all six valves on my Trident in less time than it takes to remove the rocker cover from my OIF A65. And don't get me started on how much less trouble it is to get into the gearbox on a Triumph, or how much y'all spend to make the crank get enough oil.
There's good and bad in all of them. I always dreamed of designing an engine with the good ideas from all of them.
BTW: I haven't noticed much difference in the vibration between the two twins. I have noticed that the lamps don't last very long on the A65, Could be a balance issue, neither have been rebalanced since they left the factory and the A65 is +0.060. I really don't care for either one on the motorway.

In any case, two coils replaced and the bolts thread properly, two more to be installed.
1 member likes this
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