What mileage do you get (fuel and oil)?

GSAX1 · Post by **GSAX1** » Mon Jul 23, 2007 9:56 am

Hi all.

Just wonder if my bike's fuel and oil consumption is representative. I make a note of the mileage every time I fill up and plot it in an Excel spreadsheet so the measurements are accurate.

I get an average of 3.8 liters per 100 km or 75 mpg which I think is very good considering a touring speed of about 50-55 mph and some city riding as well.

However, oil consumption is a bit on the high side, about 1 liter per 1000 km or almost 300 miles per pint. Probably half of this could be attributed to oil transfer into the chaincase, as I have to suck out some every 14 days or so with a syringe. It's much better than it was before though, since I fitted a crankshaft oil seal.

Bike is '55 twin.

Anyone else that bothers calculating their mileage?

Michael

lawrence · Post by **lawrence** » Mon Jul 23, 2007 7:59 pm

Hi Michael
75mpg! I get 50mpg on my 650 twin or as low as 40mpg if I am enthusiastic. you must ride carefully!

I was using about a pint of oil every 100 miles until Biscuit fixed my dynamo (Thanks Alan!) and now don't seem to be losing any

Biscuit · Post by **Biscuit** » Mon Jul 23, 2007 8:32 pm

We have a section member with a sixties something G12, one of those over chromed things with all the bells and whistles, and he reckons on getting 85 mpg. Me? I don't bother, it's a hobby after all.

GSAX1 · Post by **GSAX1** » Tue Jul 24, 2007 9:00 am

One of my hobbies is to calculate mileage, measure oil temperature etc.

Actually, I love to tinker with and tune bikes, and I learn something from it all the time. For me it's a great part of the enjoyment

Lawrence: I think AMC increased power a bit and at the same time increased fuel consumption when the newest cam profiles came around 1960(?). I still have the old profile cams installed and that could be the explanation. I ride quite hard actually

Unfortunately there were no official roadtests of AMC bikes in the 1950's in UK, however I have some American and German tests that show mileages around 70 mpg. Tests from the 1960's show lower mileages.

The reason why I ponder over this is that I have thought of installing the new type of cams that JSL sells, however I don't want to do that if I get much worse mileage with little (or no) gain in power and perhaps run into carburation problems as well. I have noticed that carb settings for the 500 twins with the same 376/6 carb changed several times from 1957 on and I find that a bit strange.

The oil transfer from crankcase to chaincase puzzles me a bit also. I understand some AMC twins have this problem, some not. I always thought it was the ones that didn't have an oil seal on the crankshaft but that doesn't cure it completely it seems. I have also installed a Bunn breather kit, fitted to the lower magneto bolt. I made a new hollow bolt as per Lawrence's suggestion and it works great so engine is breathing better but still oil transfers to chaincase via the original breather in the crank.

Does anyone have a mid-1950's twin that doesn't have this problem? I would appreciate some response on this issue.

Michael

Groily · Post by **Groily** » Tue Jul 24, 2007 9:49 am

I've had my 54 twin 30 years and it has always leaked from crankcase to chaincase, whether through the breather or because the oil flinger's not very effective. Both I bet. Also minor dribble at dynamo, since forever and I've given up on that. Having just had all apart to replace the gearbox guts after years of abuse - on reassembly the leakage from behind the engine sprocket was worse than ever - as in about 75 miles a pint wasted and mega-puddles when parked, natch. Have just done (yesterday) the Chris Read oil seal mod and am waiting to see what happens. Fingers crossed but it has to be far far better - will report back after a few hundred miles. As to fuel consumption, I'm a big bloke with the profile of a large brick and drive quite hard (for an old 500) - 55-60mpg is the best I have ever got except when trying to be moderate. That's been the same with a Monobloc, or more recently with a recon pre-Monobloc, set up right, and a pretty decent engine. Not that I care much!
groily

TommoT · Post by **TommoT** » Tue Jul 24, 2007 11:49 am

I have only emptied the petrol tank twice on my newly acquired 1963 G12 CSR, and it has returned about the same as Groily's, perhaps slightly less 50-55mpg. But carburation is spot on judging from reading the plugs and general engine behaviour. Idle is slightly lumpy, but maybe the cams are responsible for that. I has a Concentric Mk I. It hasn't used any oil. When i got the bike all oil had drained from the tank into the sump levelling out to the same level in crankcase and chaincase. Hardly surprising since it had been left for several years! Edited by - TommoT on 24 Jul 2007 10:51:48 AM

deshollier · Post by **deshollier** » Tue Jul 24, 2007 2:53 pm

Having no idea what the fuel consumption was on my 57 G9, and preparing to go on the International, I thought it might be worthwhile finding out what the range was on a full tank. I drained the fuel until it stopped on the main tap, added a gallon and went for a good spin until the engine stopped and I had to select reserve - exactly 60 miles per gallon. My carburation is good, the bike runs cool, i.e. rich rather than lean as indicated by my pipes which don't show a trace of blue. That is the first and last time I will check it!

Biscuit · Post by **Biscuit** » Tue Jul 24, 2007 4:02 pm

There is absolutely no need for the dynamo/crankcase joint to leak.

I fitted a lipped seal to the G11 eight years ago, it improved matters, but, defying logic, it can go for a 1000 miles or more with no problem and then suddenly, after a 100 mile run the chaincase will fill up. Does the oil come from here or is it from the breather? or does it come through between what was the thrower ring and the drive shaft, the thrower ring may be a good fit on the shaft, but not oil wise.

I have read up on the Bunn breather (never knew it existed until now) they seem a bit ambiguous as to whether you can dispense with the original breather, which to my tiny mind needs be the object of the exercise.

GSAX1 · Post by **GSAX1** » Tue Jul 24, 2007 7:19 pm

Hi Biscuit.

You have a point about the thrower ring. But it should be tight against the LH main bearing inner race, at least on my model that has the primary shock absorber on the driveshaft. I don't think any amount of oil could get past that point (between the shaft and thrower ring), only moderate seepage perhaps. Anyway it could be a challenge to seal that one..

I think the oil comes from the breather under certain conditions, which I have yet to find out...

Some older twin models (I think pre-53?) had a splash plate fitted to the centre web under the crankshaft. Perhaps the purpose of this was to hinder oil splashing around in the crankcase and beeing prone to blow out? Wonder why they dispensed with that one...

About the Bunn breather. I didn't discard or seal off the original flapper valve, I just added the Bunn breather to a hollow bolt under the magneto. No need to modify the crankcase then and it's out of sight. It's a very tight sqeeze though. No oil comes out from this one as can be witnessed by looking at the breather under operation. It's clearly visible that it flaps away and no oil is present inside it. Mag and dynamo are oil free (so far, cross fingers!).

Michael

Groily · Post by **Groily** » Wed Jul 25, 2007 7:09 pm