13 replies to this topic

[Midas Mk1]

Finally got my engine setup on the rollers today, prior to this when the clutch has been pressed, revs have dropped around 200rpm. 

Orange Pre Verto Clutch on an med lightened fly assembly.

Engine performed well and attained great results, however when im pressing the clutch in, revs are dropping more than 200rpm, with throttle needing to be blipped to keep the engine going.

 

On idle, .eg. at traffic lights, im pressing the clutch in and the car is stalling, happening both when oil and engine is warm, aswell as when cold.

 

Had a problem of the engine stalling straight away when the clutch is pressed. removed it to find a thrust washer clearance of 1 thou, now a 6thou gap.

New main bearings were fitted at this time too. 

Now is there a  problem? Any hints /ideas? The engines done about 100 miles since being built. Do orange grade clutches need time to bed in? Was pushed to 107mph on the dyno today 

Edited by Midas Mk1, 22 August 2013 - 07:26 PM.

[DILLIGAF]

No it won't bed in it'll get worse, the clearance between the crank and the thrusts is too big.......

 

You can't measure it with feeler gauges, you need a mag mount, a dial indicator and a biggish crowbar.....

 

Bolt everything back up on the block, put the mag mount fitted with the dial indicator on one end of the block with the tip of the D.I. touching the crank.....

 

Now with the crowbar lever the crankshaft,  one way. Zero the D.I. and then lever the crank the other way and measure the clearance on the dial indicator.......

[Midas Mk1]

6-8thou was recommended for this clutch / engine spec, - it's having similar symptoms to as it was when there wasnt enough tolerance and was too tight, surely it wouldnt be the same? 

Edited by Midas Mk1, 22 August 2013 - 07:50 PM.

[DILLIGAF]

That 6 to 8 thou is the clearance of the primary gear end float, not the engines thrust bearing clearance........

Edited by DILLIGAF, 22 August 2013 - 08:02 PM.

[Jordie]

you need to make sure your clutch throwout nuts are adjusted correctly. These can put some force onto the crank if the throw out isnt correct.

[JustSteve]

Does it slow the engine with the clutch only part way to the floor? 

 

try it at 3/4 of the way down, and if not, then it's probably because you've not set the throw-out properly, and the clutch plunger is forcing the crank sideways. 

[Cooperman]

A heavy-duty clutch will almost always do this. It is the result of end load from the clutch pedal being transmitted through the clutch spring to the end of the crankshaft. This presses the crank onto the thrust bearing and slows the engine revs. Just set a slightly higher tick-over to overcome this and never sit for long with the clutch down or depress the clutch pedal when starting the engine, especially when starting from cold.

A heavy clutch will always lead to quicker thrust bearing wear and as heavy clutches are normally used on very high performance or competition engines it is to be expected that these engines will be rebuilt much more often than fairly standard road engines.

Check the crankshaft end-float quite often and if it gets bigger than about 0.007" take the engine out and renew the thrust bearings. Ideal crank end-float is 0.0015" to 0.0045"

[Midas Mk1]

Thanks for the replies guys! Just been out and the revs are dropping 200 throughout the whole rev range even with the slightest pressure on the clutch. Idling around 1000-1100, when clutch pressed them its dropping to 800, then feels like its falling off the cam and spluttering to >500rpm. Idle was never going to be perfect with a sw10, want to avoid raising the idle as I don't want overun or the engine running backwards.

Really annoying me as when the cars driven, ie without using the clutch, it's performance is really good!

[Cooperman]

Urgently measure the crankshaft end float accurately.

[ACDodd]

Remove the clutch and flywheel assembly and check that the diaphragm spring is compressed completely flat when the friction plate is fitted and the whole assembly bolted together, this one is so common it bores me intensely!!

 

As also mentioned you must measure the crank endfloat to see if any damage has been done.

 

Installing the thrust washers the wrong way round will also cause this.

 

AC

[Midas Mk1]

Thanks for the replies! Going to pull it out and check the crank endfloat and try see whats the problem.

 

Clutch was assembled by med on the flywheel all balanced up, so I presumed it would be together correctly, but will check.
Thrust washers were put in the correct way too :)
 

[Cooperman]

Many years ago I built a 970 'S' rally Mini with an after-market competition clutch. It gave huge problems similar to the one you have. After stripping it, re-assembling and then stripping it again it was found that the actual clutch diaphragm assembly was distorted by a small amount, about 0.010", and this was preventing full disengagement. Another clutch diaphragm ass'y cured it completely.

Another possible cause of clutch drag is a de-lamination driven plate. It has happened but is very rare.

[Ethel]

Disengaging the clutch will also remove a bit of the rotating mass that keeps an engine idling smoothly. The effect will be greater if you have already reduced it with a skinny flywheel.

[Midas Mk1]

This is the flywheel / clutch combo I've used
http://www.med-engin...-light-assembly

Will check it when I take it out, drops 200 rpm with the slightest of touches of the clutch, I'd prosumed I'd lose some momentum, like 50 revs, but not 200.

Interesting what you say cooperman and acdodd, have noticed gear changes abit stiff, and has crunched a couple of times, being a new recon box i put it down to newness - could quite possible the clutch not fully disengaging perhaps?