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Thank you all for explaining further, it is much appreciated.
I will try and explain the reason that I’m slightly worried about the Conrod.
My Matchless has always been moderately smokey when riding. During one of the lockdowns I decided to pull the head off and investigate further.
Whilst looking at the piston and cylinder (from a birds eyes view) it appeared as if there was a bigger gap between the piston and the cylinder wall on the right side of the bike than there was on the left side of the piston and cylinder wall … in fact I was able to place a small watch maker screwdriver flathead down between the piston and cylinder wall on the right side but not the left ?
With my limited knowledge I decided that a rebore was needed … and Hamlins of Bridgwater rebored the cylinder to +20 and sorted out the rings of my new +20 piston for me.
On inspecting the bottom end … the Con Rod (from a birds eye view) I could see they the Conrod was closer to the right hand flywheel than it was to the left hand flywheel … and further more …. Whist turning the axle to make the Conrod go up and down, I quickly saw that the further the Conrod got lower between the flywheels - the closer the Conrod got to the left hand flywheel - almost to the point of kissing the flywheel- but not quite …
So I’m not too sure if the Conrod is bent ? Or if the main bearing has been assembled incorrectly? There is hardly any side to side play and there definitely no up and down play to be felt.
I rode many happy local miles for the two years I had her on the road including a week trip to Normandy with a large pillion with no trouble or noise , (apart from some piston slap that only happened the once)
I suppose I need to get the crank to Hamlins to split the crank and see if the Conrod is true -
Although it’s going to break the bank , I think best to replace the bearing and Conrod whilst it’s down this far - I’ve always worried about Conrods snapping with age and ware ! Is this something I'm over thinking 🤔
I will endeavour to post some pics tomorrow - thanks for reading …
email (option): Towersmark84@yahoo.co.uk
Mark, best get a report from your engineers next. 'urry up! you've only got four months:scream: Ron
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It sounds from your description there is a prospect the conrod is bent....It was not uncommon for rods to be straightened and reused and many publications from the period detail the procedures required...I've done them myself a number of times as the M20 rod in particular is relatively weak in one plane...
Regarding failures of steel rods that is generally restricted to either tuned engines or extenuating circumstances, such as a lubrication failure/piston siezure etc....I don't recall ever seeing a simple broken rod in a standard or 'cooking' engine..
However, as you will have to pay for someones time to check and straighten it, a new rod might be the better option if you can obtain one at a reasonable cost...Ian
Just out of curiosity Mark, does your conrod look like this?
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I have a lot of used conrods and some used two piece pins used hence Genuine. small and large diameters They are reconditionable if you have the skills. I have both long and short rods, not sure how mamy of either.
I also have a very good broken one piece pin if you want to know why they are not good, also the broken crankcase that resulted.
No my Conrod is a similar design but has no cast markings on it like the one in your photos has.
My Conrod is plain on both sides.
Update - Hamlins have now examined the Conrod and have confirmed that it is indeed bent.
I am now waiting for an update on the condition of the crank pin and of the main bearing and little end.
My wallet is crying already - but doing my best to make Normandy in June Ron 👍🏻👍🏻
I will keep you all posted and will add some photos soon.
email (option): Towersmark84@yahoo.co.uk
I have spoken in the past to Autocycle engineering, he has taken over Alpha from Max Nightingale after his death. He said that the one piece crankpin are ok on the 350 engine, but not on the 500. He has never heard of one snapping on the 350 but has on the 500, the biggest problem that he highlighted was that they are now available in oversizes to compensate for worn flywheels and does them in oversizes, from experience I’d suggest if yours feels loose in the flywheel to send it to him to have a pin made to suit. They should really go in with a crack as they press in (yes, that tight!) from my experience the holes are not totally round and you may have an issue getting the pin to go in straight without peeling back some of the metal in the hole and causing problems trueing the crank. I do lots of cranks but these can be problematic if you get it wrong. So reluctantly I’d suggest getting them to fit it. I believe he does both types of pin, both one and two piece.
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