Turning over engine

DrMike · Jul 24, 2013

Hi all
New member, new to commando's, and happy to be part of the community.
I am trying to time my 74 MKIIA and am turning the engine to find TDC, although this is not a TDC question. Two things are noticeable:
1. I cant turn the engine (plugs out) by turning the rear wheel, but I can by pushing on the kickstarter. Most forum comments on this just refer to turning the wheel. Is there a reason for this? I have the bike on the centre stand. Ive tried it in both 1st and 4th, I would have thought it easier in 1st, but there seems no difference - it just wont go by hand, and Im really applying some pressure.
2. Following on from this I notice there is free play in the rear wheel when I do move it by hand. The wheel will rotate about 20 degrees (3 inches or so at teh tire) before it engages either way with the rear sprocket. I thought the sprocket/wheel arrangement was fixed.

Id be really pleased for some insight.

cheers

Mike

Rohan · Jul 24, 2013

If you put it in gear, any gear, up on the centrestand, and use the kickstarter, does the wheel turn as well.
It should.
(as long as its off the ground).

With the plugs out, and in gear, you should be able to relatively easily turn the engine over.
(with the wheel not firmly planted on the ground).

In neutral, can you easily spin the rear wheel.
(with tire not touching the ground).
It should easily spin, and spin and spin.

There is a cush drive in the rear wheel, but I'm not sure how the Mk3 one works compared to earlier 850s.
There is also a chain tensioner in the primary of a Mk3, which is different to all earlier Commandos.
Maybe this has something to do with this ?

1up3down · Jul 24, 2013

ah!

yes, you CAN do it!

but not by just putting your hand on the rear wheel and pushing forward unless you beef on it good

put it in fourth and grab the rear wheel and yes you can kind of gently "jerk" it forward in little encouragements to move motor, all you are doing is snapping the chain a little, no harm elsewhere!

DrMike · Jul 24, 2013

Hi all
thanks for that input. I havent tried to jerk the wheel, just put steady force on it. I will give that a go. It does turn ok (and relatively easily) via the kickstarter, and yes the wheel turns with it. It just strikes me as odd that everyone says turn the wheel but really that doesnt seem so easy to do - except by the kickstarted, and that makes peering in the primary timing access port difficult.

Regarding problem 2, the cush drive mechanism in the rear wheel makes sense, so Im not so worried any more, although it does seem to have more play than I would have thought desirable.

So- 1 post, good answers in an hour - great forum. Happy to hear any other views or advice on this.
thanks

Nortoniggy · Jul 25, 2013

You'll find it easiest in 4th gear.

Ian

ashman · Jul 25, 2013

Give it a few good jerks but when you come up to or near the timimg marks just give it light jerks as it is so easy to over shoot the marks and yes it is easyer in 4th gear, these bikes have so much compression, but its easyer doing it in 4th gear than on the kicker, you can control it better.

Ashley

Matt Spencer · Jul 25, 2013

:shock: The TERM

is ' Nudge ' . Judiciously .

concours · Jul 25, 2013

DrMike said:
Hi all
New member, new to commando's, and happy to be part of the community.
I am trying to time my 74 MKIIA and am turning the engine to find TDC, although this is not a TDC question. Two things are noticeable:
1. I cant turn the engine (plugs out) by turning the rear wheel, but I can by pushing on the kickstarter. Most forum comments on this just refer to turning the wheel. Is there a reason for this? I have the bike on the centre stand. Ive tried it in both 1st and 4th, I would have thought it easier in 1st, but there seems no difference - it just wont go by hand, and Im really applying some pressure.
2. Following on from this I notice there is free play in the rear wheel when I do move it by hand. The wheel will rotate about 20 degrees (3 inches or so at teh tire) before it engages either way with the rear sprocket. I thought the sprocket/wheel arrangement was fixed.

Id be really pleased for some insight.

cheers

"

Mike

"I would gave thought it easier in 1st"

The mechanical advantage is for the engine driving the wheel. To drive the ENGINE from the WHEEL, 4th gear gives the most mechanical advantage. It's bicycle sprocket 101. Remember this for future use, should you ever need to bump start the bike. It will make the difference between skittering to a stop and roaring away.

As for the backlash at the hub, it's the "almost a cush drive/quick release" hub's hard plastic inserts have crumbled and fallen out as dust. Easy fix.

pete.v · Jul 25, 2013

I do not think you will find TDC by peering into the timing hole. If there was a mark, which there is not, you would still have to validate it with a timng wheel on the crank, a piston stop and the primary cover off.

Yes, forth gear nudge. 3" of play is normal at the wheel.

Holmeslice · Jul 25, 2013

Doctor,

4th gear is easiest. It will take some effort. The slop you are feeling is probably not cush at all, but simply the tolerance between gears in the box, which increases as you add sprockets, chains, and distance. Very normal.

You will need a piston stop, or at least a dial indicator, to accurately get TDC.

We are in the ' hood, so give us a ring if you get stuck.

-Kenny

Hobot · Jul 25, 2013

If you ever roll start by yourself on level surface you'd better be in 2nd or above or likely just skid the rear on clutch release. Be careful of sticking something fragile in plug hole to stop piston in both directions to zero in on TDC as the plugs are angled the piston presses on the probe more sideways than vertical dead on. BTw most the slop is taking slack out of chains, next is cushions slack and rest the slight gear train slack. There is enough resistance from tire to crank that I have to bump wheel against the turning slack to get engine to turn a bit, then bump it back some d/t over shot. Once able to start I find fine tuning initial timing by setting just short of back fire hints starting then put a mark on then put a light on to give it a number and judge how far off or on the factory dial is. They sell a piston plug stopper tool.

jaydee75 · Jul 25, 2013

pete.v said:
I do not think you will find TDC by peering into the timing hole. If there was a mark, which there is not, you would still have to validate it with a timng wheel on the crank, a piston stop and the primary cover off.

Actually we MK3 owners are fortunate enough to have a timing mark on the crank and a peephole, which should be very accurate. But I noticed that this one is not a MK3, so N/A.
Jaydee

concours · Jul 25, 2013

"Following on from this I notice there is free play in the rear wheel when I do move it by hand. The wheel will rotate about 20 degrees (3 inches or so at teh tire) before it engages either way with the rear sprocket. I thought the sprocket/wheel arrangement was fixed."

Pretty straight forward

pete.v · Jul 25, 2013

jaydee75 said:
pete.v said:

I do not think you will find TDC by peering into the timing hole. If there was a mark, which there is not, you would still have to validate it with a timng wheel on the crank, a piston stop and the primary cover off.

Actually we MK3 owners are fortunate enough to have a timing mark on the crank and a peephole, which should be very accurate. But I noticed that this one is not a MK3, so N/A.
Jaydee

Click to expand...

Damn those MKIII's. Get yer own freakin forum!

slimslowslider · Jul 25, 2013

3" play means the cush elements are shot, the "pushed" ones might even have gone. The standard ones are out of some kind of hard plastic and have almost zero resilience. I replaced the worn ones on my Mk2 with MK3 elements cut to shape. The Mk3 ones are out of rubber.

DrMike · Jul 25, 2013

Thanks again to all. It should have been obvious to me that 4th gave the most mechanical advantage going from wheel to motor - physics 101 indeed. Problem 1 solved.
I will check the play in the rear wheel a bit more accurately and see if I come closer to an answer on the cush drive - it didnt strike me as a problem when riding, but its worth more of a look.
cheers

Hobot · Jul 26, 2013

Should get maybe an inch motion from good shape cushions and another inch or so from the chain slack. Least slack is nicely noticeable on the ride smoothness of frame-supsension lurch on throttle ups and dns. Also seems to let the iso's isolate a bit sooner and deeper. Side slack in swingarm adds to the slack taking up sensations. Too loose or worn primary chain can add annoying slackness too, especially if the sleeve bushes allowing clutch wobbles. Ah so the ever narrowing down expanding focus to aspire towards a "fully fettered" Commando.

Turning over engine

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