There was some talk a while back where some other Loop Frame was suffering vibrations at some speeds. I said at the time that mine (Jug) didn’t do this, but in fact it does.
My speedo on the bike reads substantially over, but via the power of GPS I can advise that once heading north of 65 MPH mine does get a little vibratory. As in, enough to make 65 a preferred cruising speed. It’s quite a light buzzing.
I’m in the fortunate position of being able to directly compare with an 850 T3 (Blue). That bike is noticeably smoother and I’m happy to cruise that in the 80 – 90 range all day. Noted that the red line on the Loop is a whole lot earlier in the rev range, though I’m nowhere near approaching that in this speed range.
Now Jug has previously been fitted with mounts from the dynamo cradle up into the frame rails – presumably to circumvent the known issues that can arise with the cradle. Mine looks OK so as a first port of call should I perhaps try removing these?
Beyond that I can say that the bike came with receipts for a lot of engine work, and I have a recently fitted new UJ on the bike.
Well the preferred cruising speed for me would be a genuine 75 per on main roads. And it do still buzz at those speeds. I suppose I was looking more for a general view on whether they are all a bit like that. I know if there were more people here we’d be getting into discussions on carb balancing and the like, and to those spectres I can only say that the bike is serviced and that is all done, and the bike is running points on the original dizzy.
I note that on the rev counter the red line starts at maybe 6.5k on this bike whilst on Blue it is 8k. I was wondering what the difference is in engine architecture that forces this difference?
As to doing higher speeds - the engine can surely take it and the bike feels planted well enough. It’s just the brakes that are piggin awful.
I don’t have trouble cruising at 75mph on my 1971 750 v7 special, as you say the bike is planted but I don’t find mine buzzes through handle bars or the foot pegs. I have the bog standard twin leading shoe drum brake on mine. I use a Venhill cable and shoes from villiers, I spend time to set them up as per Greg Benders this old tractor website ditto back brake. I find the brakes give plenty of feel and I can lock up the back wheel if not careful. I still get a Mot on mine and I always ask how are the brakes, he says they are a better then some of the disc brakes he comes across.
I do balance the carbs with a carbtune quite often (only takes 10 minsj as they can go out of sync quite easily and that makes a difference to smooth running, even so 75mph should be easy to cruise at. I run points and original distributor and do the timing with a strobe
Good luck
Ian
OK - thanks for that.
As a plan, if I assume there are no mechanical forces in play here then I think I’ll;
. Recheck the carb balance
. Check the ign timing on both sides
. Remove the non-OE dynamo support struts
Not sure when I’ll get round to that but I’ll report back once that’s done.
I’m running an SP370 on short gearing as my daily driver at the moment, and as a non-balance shaft single that might desensitise me anyway.
Mine has a bit of vibration but I think it’s more related to engine speed than road speed. Generally I stick to indicated 65mph as that seems to suit the bike, but have also spent long periods at indicated 80mph when on motorway.
I agree that carb balancing is worthwhile although has more effect on throttle response at lower rpm I think. If you’re running with an original distributor it will be single points, so not much opportunity to set left/right timing.
Since owning my Spada, I’m tending to use higher rpm on the loop rather than slogging at low rpm. I think it actually suits it better.
I’ve been out on mine today and took note of what was going on, and at 4500 revs I was going 75mph (on my speedo). I would say that the handle bars felt fine, no vibration or buzzing but I now think I could detect a slight tingle through the foot-pegs. I find the engine is definitely happier (smoother) at higher revs. I was also 2up.
Cheers
Ian
Hi, just read about your eldo buzz, whan i was rebuilding my eldo i was very aware of the need to strengthen the alternater support, i did it by useing an old mini valve spring sited near the back of the alternater and fixed to the underside of the frame this fixing is adjustable so that i can get what i think is the right pressure pressing down on the alternater with a shaped piece of hardwood locating in the bottom of the spring and around the top of the altenater, i then put a piece of hardwood under the back of the alternater cut around the ribbing on the top of the engine and painted matt black. Ive had no trouble with this cobbled up support and ive done about 3k miles and been over some horrendous bumps and even been airbourn on some of the B roads around the Somerset levels these roads are particularly undulating and can catch you out sometimes. This might sound a bit of a complicated fix but if you see it its quite simple and easy to do.
With Blue my T3 back on the road now I find that much happier and smoother at speed - cruising 85 (actual) with no discomfort.
I’ll check the service items mentioned on Jug, then remove the dynamo supports for a test run. If that proves damming then an alternatively engineered arrangement as suggested above might be the way to go.
Hey - thanks for that. I’ve not actually moved forward on this since my last post. I’d kind of convinced myself that it was worse in my head than it actually was. But having taken my T3 - Blue, to the Pennine rally and then run Jug again I realise that something is defo not right.
I have access to materials, cutting tools an a stick welder so need to get my act together.
Not yet, I’ve been all a bit tied up. I’ll defo be doing that over winter though it may be Spring before it gets a decent ride out. And I’ll be servicing at the same time including carb balancing and ign timing checks.
Work is all done, just got to button it back up again - which should happen tomorrow. Not sure when I’ll get to ride out, and it will need a decent run to warm through before trying some higher speed cruising. If that’s a fail then I’ll need to be a little more attentive to settings and adjustments at the early spring annual service I guess.
First impressions are that it is no better. Probably. More attention required for other setting at the next service maybe. Maybe the loop frame just transmits more vibes generally.
