Hitchcocks Forum

Bike is a 2019 C5 Classic.
When I first started opening the bike up a bit after running in, the engine vibration was horrendous over about 55mph in top.It nearly had your eyeballs out!
Now, lots of folk said it would improve with 2/3k miles up the bore so I stuck with it.
I'm now at 2250 miles and over the last 2/300 the vibration has just about gone!!
Don't get me wrong, you still know you're on a 500 single but it's not at all annoying anymore.
If I hadn't had the assurance that it would improve I could well have flogged it. It was that bad.
The bike also seems to have found another 4/5 horses from somewhere but perhaps that's just 'cos I'm able to use the revs now.
I wonder if that's why you see so many for sale with only a very limited mileage?
So, if you're thinking your new bike is not for you because of vibration - stick with it!

Can anyone explain why this should be so? OK, so things are bedding in, but what was vibrating before which has now stopped?

all the loose bits that were vibrating have fallen off...

Probably settled into it's natural harmonics in the engine mounts. There's more movement there than you'd think on most bikes and actually quite a lot on an enfield. The engine is part of the frame and how it's connected (say more load on a front mount than a back one) can make a real difference. I know on the iron barrel ones, the engine actually holds the frame together, you need to spring it all into place to get the bolts in so you can get some really odd harmonics going with steel in elastic tension attached to a big vibrating motor.

If I get a lot of vibes on a bike, I'll often loosen the engine mounting bolts. If it drops down, I nip them up again. If it doesn't I jack up under the engine then nip them up again. Might make it better, might make it worse.

Thank SW, good tip.

The idea is to juggle all the vibrations until they appear six inches behind the rear end of the exhaust pipe.

On my 612 at idle, the front wheel visibly rolls back and forth slightly as the forks flex in time to the engine turnover. If you pull the brake on, the bike starts to vibrate instead.

That’s alright. Trick is to ride fast enough to overtake the vibration. If you go too slow, the vibration will only travel as far back as the rider.

And that’s my excuse, your honour!

stinkwheel wrote: ↑

Sat Jul 11, 2020 7:43 pm

There's more movement there than you'd think on most bikes and actually quite a lot on an enfield. The engine is part of the frame and how it's connected (say more load on a front mount than a back one) can make a real difference. I know on the iron barrel ones, the engine actually holds the frame together, you need to spring it all into place to get the bolts in so you can get some really odd harmonics going with steel in elastic tension attached to a big vibrating motor.

If I get a lot of vibes on a bike, I'll often loosen the engine mounting bolts. If it drops down, I nip them up again. If it doesn't I jack up under the engine then nip them up again. Might make it better, might make it worse.

I've been thinking about Stinky's comments and they make a lot of sense to me.
Enfield frames are definitely held together by the engine to a large extent. You'll know if you ever had to re-install one.
It seems to me that ALL the stressed members of the frame need to be in tension?? Dunno, I'm no engineer.
I wonder if the factory builds them on a jig that does not have the engine in tension and after a few k miles the engine settles into the frame, possibly in an instant, which helps to subdue vibration?
If this is the case, then slackening engine mounts, then taking the bike OFF the centre stand (and possibly with the weight of a rider on the bike) should settle the engine in so it's in tension?
Or am I talking bollocks again Not unknown.

I don't even know if it's something as specific as that or if the jiggling manouver I described just moves things to somewhere slightly different, altering the resonant frequency. Like adding or removing half an ounce on a bar end weight can make the difference between comfort and being unable to read the roadsigns.

I've done similar with japanese bikes with cradle frames in the past too. My KLE500 vibrated like hell at about 70mph when I first got it. Loosening then tightening the engine bolts almost totally cured it.