In writing the following lines, I will, no doubt, absolutely confirm the fact that I am a total Austin Seven incompetent, despite an on and off love affair which now fast approaches half a century ( indeed exceeds, if I count in my boyhood experiences)

The December 1928 Chummy which I currently have on the road was purchased from Queensland going on two years ago now. It was/is in absolutely first class mechanical condition, having been totally "refreshed" by one of Queensland’s real A7 guru’s.

It has a “1937” Head and an SU carby, Phoenix crank, slightly ground camshaft, a lightened flywheel and the standard 3 speed gate change gearbox. It goes like a dream, and is easily the liveliest A7 I have ever driven, and even stops well!

So, against that backdrop I will outline the following problem, well, not really a problem, more a “quirk.”

I have had experience of crash gearboxes since first learning to drive, and consider that I can “double de-clutch” as well as anyone.

Now in my Chummy, I have no trouble dropping back from top to second, or second to first in virtually any circumstances.

But I am intrigued by the fact that when I go from first to second, and second to top, at what I would consider appropriate road speeds and circumstances I frequently “grind the gears.”

I have developed a technique to avoid such mechanical mistreatment of the gear box by very slightly “blipping” the throttle during what would normally be the relaxed throttle period in neutral during the change.

I don’t remember this being the situation in my previous cars, although none of them have had lightened flywheels.

The only thing I can think of is that the lightened flywheel allows the revs to drop faster than would be the case in a “standard” flywheel engine.

Is there anyone out there in "Austindom" who has had experience with the crash box and a lightened flywheel?

Do I simply need to continue my “blipping” (to use the technical term) during such gear-changes or am I doing/is there something else wrong?


Barry R.

Barry

I have a 4 speed synchro box with poor synchro. Down the box is fine, but up from 2nd into 3rd often "graunches". I tend to double de clutch on this change, although when its warmed up it gets better.

However I also drive on occassion an old Zetor tractor with a five speed crash box. The instruction book states that I should "blip" the throttle during down changes whilst double de clutching, BUT not "blip" on upchanges? Experience has proven that this is indeed the case and gear changing can sometimes be OK. Conversely with the Colander I do have to "blip" slightly on the upchange to avoid the crunch, non "blipping" results in a crunch??

I guess its all about matching the speeds which would give your theory on lightened flywheels some credibility if indeed the engine does rev up and down more quickly?

Steve

Yes, this is a by-product of a lightened flywheel. If you drive cars with, and without lightened flywheels it is also easy to mix the two up!!

I only have one Seven these days (with a seriously lightened flywheel) so I least I don't have that problem any more.

STEVE JONES

The point in double de-clutching is to synchronise the speeds of the output gear relative to the layshaft. In a 'crash' box, the gear itself is straight cut and won't match with it's partner on the layshaft unless their relative rotational velocities are roughly equal. When they're not, and you force them into mesh you get that horrible grating noise.

The purpose of a throttle 'blip' is just to raise the speed of the layshaft to enable the desired gear to mesh without leaving it's teeth in the bottom of the box. Most A7s with a heavy flywheel take quite a while on an upchange for the intertia to be lost, but if the flywheel has been lightened this will happen quicker and a touch of throttle may well be necessary just to bring things back up to speed.

Eventually, you get an 'ear' for it, and if you need to practice, try driving your modern (assuming it's a manual) without using the clutch to change gear. You'll see that you do have to give a squirt of gas even on an upchange because if you try and rush it, it won't go into gear unless you force it, and that's wrong. It should slip into gear as easy as a knife into butter if you've "sunchronised" it properly.

Don't try and do racing changes. You must give the gearbox & flywheel their own time to come together. Try counting "Clutch one thousand, (neutral, up clutch), clutch two thousand" and you'll not go far wrong.

Gentles,
Thank you all very much for your responses.
I thought that the lightened flywheel was likely to be the main culprit, but was concerneded that, in my dotage, I was contributing something to my dilemma.

Ah, another log on the fire, another dose in my port glass and I will further contemplate the perfection of my "Blipping"

Go carefully


Barry R.

Barry, just a thought!
If you increased the tick-over speed of the engine it might prevent the revs dropping too low when changing up. It would have no effect when changing down.

Good Forum this isn't it !

Thanks for that Malcolm. I have "played" around a little bit with the idling, but think I would have to raise it too much.

I will have the Chummy out tomorrow and will have a further fiddle anyway.

I am reasonably happy now that I have "confirmed" that the lightened flywheel is the base problem. I have managed to quite adroitly adapt my "blipping" to suit, and crashes are now very very seldom...

You are spot on Malcolm, this is a fantastic forum and I find myself learning new things all the time!

Even in those areas where I think I have some experience, I have enjoyed having to think out things properly, and sometimes I have to concede that what I have always taken for granted, is not necessarily so.

It is certainly possible to teach an old dog new tricks!

One thing that I really do think we need to ponder upon is just how some of the stuff on this forum could be archived and accessed.

There is a real fount of knowledge out there and I really appreciate this way of tapping it.


Regards to all,

Barry R.

.

Barry,

When you are out tomorrow you could try beating the rev reduction by making a change without double de-clutching. It may just be that with the lightened flywheel the double de-clutching is just all taking too long, and is actually un-necessary. Indeed this seems it be the case if you are having to blip the throttle.

It used to work for me with a similar engine.

Mike

Thanks to everyone who responded on and off the Forum on this item.

I am now totally satisfied that the lightened flywheel is in fact the root of my "troubles" and I have just about refined my "blipping" to give virtually 100% quiet changes. Don't know how I will go in my son's Morris Cowley after all this though!

I am amazed at just how quickly the revs seem to drop off as a result of the lighter flywheel and yet the idling is still smooth.

Put in around 60 miles in the Chummy today. Glad I checked the wheelnuts before adventuring out though. Must make this a regular routine.

Also have to do something about fitting sidescreens. Nice blue skies here today, but pretty fresh, not much more than 10 degrees C.

I think an oil change and grease up will be on the jobs list for tomorrow.


Thanks again for your responses


Regards,

Barry R