Vibration and engine seaze

john a sheppard · Post by **john a sheppard** » Sun Mar 22, 2009 2:53 pm

I have just completed restoring 500 single 1954. I had the engine rebored and new piston and big end. The bottom end was a 350 but I exchanged the flywheel for a 500 at Jam Pot when I had the rebore and new big end done. When it started the oil flow seemed fine with the return clearly seen in the oil tank. I have started ridding it and have got upto 90 miles. However, above 50mph the vibration in the seat and handlebars makes it almost unridable. Yesterday I did try to get it up to 60 to see if I could get beyound the vibration but the engine ceazed and of course I am now lucky to be alive as there were no other cars around. I am convinced the vibration and the ceazing are linked in some way. Once the engine cooled a little it restarted. (I cheked the rear wheal and that was fine spinning without problem). I have cheked the bore and although marked does not seem particulary damaged. Has anyone elce had this experience.

Rick.Edwards · Post by **Rick.Edwards** » Sun Mar 22, 2009 4:31 pm

John you have to run them in!

laxy · Post by **laxy** » Sun Mar 22, 2009 5:33 pm

Hi John, Yes, I had similar problems with my newly rebuilt engine on the 1951 G80.
Not the vibration but during the running in period if I tried to exceed 45 mph the piston would seize within half a mile.
It was still doing it after 1,500 miles when it should have been well run in so after removing barrell I found light score marks to front and rear of piston but no damage to bore.
I polished the marks out of the piston and re-assembled and the problem never occured again.
It turns out that the piston supplied by JSL needed a lot more clearance than the standard item but no one told me that so I just followed the info. in the manual regarding piston to barrell clearance.
The vibration you describe may or may not be connected to the piston problem.
When the crank assembly was built up were the flywheels trued up?
this makes a big differance to how smooth the engine feels.
There are many reasons for the vibration but get the piston sorted and take it from there.
Regards Keith

john a sheppard · Post by **john a sheppard** » Sun Mar 22, 2009 7:39 pm

Dear Keith.
You have described the scoring I have. I will remove the barrel and re stone it to see if I can get rid of the scores. Thanks, I feel much better knowing somone elce had had the same problem. I am at a loss with the vibration. The fly wheel was trued up. Do you find you can do more than 55 mph in comfort?
Best Regards
John Sheppard

itma · Post by **itma** » Sun Mar 22, 2009 7:53 pm

The damage will be on your nice new piston.
Take it off with a fine oil stone and live with the rattle.
Any flywheel assembly should be handled with kid gloves,as i wil not take much of a knock to misalign it, and a little will cause a lot of vibes.
Vibration such as you describe can come from many sources, a badly assembled engine into the frame; missing head steady; undersize replacement studs; over advanced ignition.
You really pushed your luck in this instance with a new piston and bore.

laxy · Post by **laxy** » Sun Mar 22, 2009 9:58 pm

Hi John, Yes the 500 single should be comfortable and reasonably vibration free at that speed.
Solve one problem at a time. piston first then vibration which can be down to loads of things,some already mentioned plus wheels out of balance, loose ANYTHING,main bearings shot etc etc

mikeydpippin · Post by **mikeydpippin** » Sun Mar 22, 2009 10:39 pm

I'm interested in the answers on this problem.I have replaced my piston but kept the original barrel,cos the barrel looked good. I have kept speed to 45-50mph max,with the intention of running in for 500 miles.the engine wil tell you if it's struggling.So far so good 130 miles now and she runs and sounds puuurfect.
I've rode jap bikes and a Royal Enfield (revisited model) and i must say my Matchless has something special,this bike is favoured over all the others,because of speed NO because it has the X factor," a gem to ride". In fact today someone suggested it was a Heartbeat bike but i dont think these were used for that program "were they".

Rick.Edwards · Post by **Rick.Edwards** » Sun Mar 22, 2009 11:22 pm

PC Walker had a nice G12 CSR at one stage.

TommoT · Post by **TommoT** » Mon Mar 23, 2009 2:15 pm

Vibration is often a telltale of something starting to go amiss, unless the vibration experienced is part of the design, and thus to be expected. On a single there is a lot of built-in vibration, but I can easily go 55-60mph for hours on end. In the end I have to get off, to unfold myself, and try to get some blood into those white knuckles and finger tips! But apart from that, no worries.

Incidently my G80 is fitted with 350cc flywheels, but when it was re-bored last, the engineer checked balance factor, and it was within limits.

I work with helicopters in my daily work, and vibration monitoring is a big thing in these contraptions. All rotating axles and bearings are monitored by vibration sensors. Data from these are collected and read out after each flight. The vibration pattern is then compared to that of a new part = known base values. If the vibration pattern is out of limits, the part in question will be changed and depending on a thorough examination it will either be refurbished or scrapped.

As an example: before a gear wheel sheds a tooth, the molecular structure of the metal will change ever so slightly. In the beginning this cannot be detected by eye or testing, but the vibration pattern changes, and can be picked up by a sensor. This change is then recorded and read out and the gear wheel can be changed before it collapses. Very reassuring if this gear wheel is fitted to the main gearbox output axle on a helicopter! You know, no rotation on the mainshaft = zero uplift!

I have been thinking of fitting such a system to my G80 but I guess the readings would be all over the place, all the time.

As an aside you have probably pushed your newly re-bored bike way beyond safe running in limits.Edited by - TommoT on 23 Mar 2009 2:17:06 PM

thomthom · Post by **thomthom** » Mon Mar 23, 2009 7:21 pm

Blimey Tommot, Do you think your G80 will drive a helicopter