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Discussion Starter · #1 ·
Hi everybody out there in biker Heaven.

I have recently got my 1966 Bonny back together filled it with oil and started to time the engine-kicking it over I eventually got it going and how it went! like a demented charge of a wild beast the noise was deafening (alright I hadn't put the baffles back) and the carb was out but it soon came to an abrupt halt and would not fire again.

So much to my dismay I started to strip the engine down to find the head and piston crowns pretty much as you would expect to find them-then turning the engine over whilst looking down the barrels only one piston came off came the barrels and as you can see from the pics my poor left hand conrod was nothing but mush resembling mashed tinsel and breaking it's way through the cylinder liner and piston wall leaving a pretty new silver speckled redecorating job on the bottom end walls.

Prior to this I did a valve job and put a recon head on,I also observed that both piston rose and fell together with one minor strange observation-one piston appeared millimeters lower than the other-alarm bells should have started ringing and yes it was the same piston that broke it's conrod.

I may not have connected the oil hoses on right
(feed front return rear) or the push rods may have got swopped over.

I'm currently stripping it all down and considering my options and do not wish to repeat this what looks like an expensive rebuild.

I have a few questions -

Can I obtain any blueprints of a '66 bonny to check cam to tappet to pushrod to rocker valve to piston dimensions and clearences?

Would getting push rods mixed up or tappets cause such a meltdown?

I have a Haynes manual and pdf format workshop manual upto pre concentric carb models.

Has anyone got a copy of "Hughie Hancocks Triumph Unit 650" dvd they could sell me?

many thanks for any input Steve


Super Moderator
14,016 Posts
Welcome, and sorry to hear your tale of woe (or was it whoa!?).

The problem existed before you assembled the top end, it was in the existing connecting rod. You can mix and match pushrods & tappets (cam followers) without anything this serious ever happening.

Make sure to clean out the sludge trap in the right side of the crank hen you get the engine opened up. I'm guessing you will need to have your crank journals ground and install undersized connecting rod big-end shell bearings.

Any shop manual will have all the correct engine specs and tolerances. I suggest the "Kim the CD Man" Triumph 2-disc set.
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