Flywheel clearance


Date: Fri, 06 Nov 1998 02:29:32 -0700
From: David John Edge
Subject: [imps] Flywheel clearance

Hi all,

Just after a spot of advice,
my 930 B1 block,
how much clearance do I need between the flywheel and those ground off flanges on the new block. When I originally installed the engine, I didn't take enough material away (2mm clearance) and it made a light scraping noise when the clutch was depressed, when I took the engine out at the weekend, I ground the ones that were visibly marked by the flywheel. Problem is that now only one of the flanges is being contacted and it can send the flywheel into a wierd vibrating state.

Oh yeah, for all you holding your breath on my engine removal and clutch replacement: It took 3 hours, no bruising was experienced and only one cut was sustained to the right hand. I was sitting inside the engine bay, levering the clutch release arm over the retaining spring and no word of a lie, I was heard to utter the words 'Hey, Rich, guess what.. I haven't cut myself yet' The screwdriver slipped and my hand hit the bellhousing. DOH!

The engine is coming out again this weekend for the block cutting to avoid the flywheel. P.S. I can drive it to avoid this happening so it isn't dangerous but needs fixing.

Dave


Date: Fri, 06 Nov 1998 15:18:33 -0100
From: rienk steenhuis
Subject: [imps] Re: Flywheel clearance

Hello Dave

>When I originally installed the engine, I didn't take
>enough material away (2mm clearance) and it made a light scraping noise

I've looked up the endfloat on a normal imp crankshaft for you, and it's 0.002 to 0.01 in. or 0.05 to 0.25 mm. So 2 mm should be more than enough.
Perhaps check thrust washers?

Rienk


Date: Fri, 06 Nov 1998 07:30:58 -0700
From: Dave Edge
Subject: [imps] Re: Flywheel clearance

Reink,

There is plently of clearance when the engine is just running. The problem arises when I press the clutch. This produce forces on the flywheel which make it flex slightly. When it does hit the flanges, it bounces back because it is only hitting one flange. Before it used to hit a flange, bounce off and hit another flange without flexing much, it is now allowed to flex because I have removed more flanges so there is nothing to check the flexing. (I have just re-read this to make sure it makes sense - it doesn't, sorry!)

It's a brand new engine with correct endfloat.

Dave


From: Nickcleak@aol.com
Date: Fri, 6 Nov 1998 15:24:33 EST
Subject: [imps] Re: Flywheel clearance

> This produces forces on the flywheel which
> make it flex slightly.

ummm ... Flywheels don't flex .. they are rather solid ! Do you have a thin lightened one ?

I have about 3mm clearance on my 930 as you engine is out just get a good clearance , this should be ok i would think ..

Nick ...


Date: Fri, 06 Nov 1998 21:32:58 -0100
From: rienk steenhuis
Subject: [imps] Re: Flywheel clearance

Hello Dave

>There is plently of clearance when the engine is just running.
>The problem arises when I press the clutch. This produce forces
>on the flywheel which make it flex

I guess the force needed to depress the clutch-pedal won't be more than say 10 Kg. From this I think the force on the clutch itself is something like 160 Kg. (10 X 5 x 2 x 1.6) X 5 for the pedal, X 2 for the cylinders and x 1.6 for the leverarm. Which is a fair bit. But the flywheel is just under 10 mm at the thinnest bit on the center and nearly 1 inch for the main body. I can't really see it flexing by 2 mm.

What I would do in your case is before removing the engine have a look underneath the car where you can see the flywheel. (take the bit of gauze of) Have someone depress the clutch for you. if there really is considerable flex it will be clearly visible against the bell housing.
But check the pulley side as well. With the clutch released push it in and see if it moves out when pressure is aplied. The only other explanation I can come up with is some material between the engine and the flywheel. I've seen a release-bearing retaining spring having come undone and getting stuck in there.

You're not the only one who keeps getting his knuckles chafed. And using screwdrivers for something they're not made for is a mayor health hazard. :-)

Rienk


Date: Fri, 06 Nov 1998 15:28:53 -0700 From: Dave Edge
Subject: [imps] Re: Flywheel clearance

Hi all,

If you put enough torque though anything it will flex. Have a look at the thickness of torsion bars. Reink is quite right, they are weakest by the crankshaft because they are thinnest there. Good advice by the way Reink, if the clutch is pressed there is no visible movement of the flywheel when the engine is off but with it running it only has to chatter a bit on the flanges with about 2500 rpm and it goes ape because constructive interference is set up, ie one pressure wave combines with another pressure wave instead of the destructive interference I was getting with more than one flange getting in the way.

My flywheel is std I presume but then again I have no proof especially in view of the fact that when I got the car it had a competition friction plate and that rally box (thanks all for help with its ID). Perhaps I will weigh the flywheel, isn't it supposed to be 15lbs?

> Flywheels don't flex .. they are rather solid ! Do you have a thin
>lightened one ?


From: Gary and Carol Henderson
Date: Sun, 8 Nov 1998 00:17:46 +-1300
Subject: [imps] Re: Flywheel clearance

Hi Dave

Is it possible that the flywheel had hung-up slightly on the dowel, when tightening it? This would leave it loose on the bolts eventually, but still centred on the crank & powered via the dowel.

Good hunting
GaryH