Clutch Shenanigans

[VitesseEFI]

My son has classic engine-swap disease…. Probably my fault.

He's been busy putting a Ford Sigma 1.6 from a Mk1 Focus in his Spitfire MkIV. Doing a nice job too (obviously I’m biased)

To complicate matters he’s used an NA Mazda gearbox, which is not even nearly a natural fit on the Ford engine or in the Spitfire. This has involved grafting a section of Ford bell housing onto a cut down MX5 front casing and a concentric slave cylinder.

https://sideways-technologies.co.uk/forums/index.php?/topic/7107-chriss-mkiv-basket-case-restored-to-glory/page/14/#comments

It’s getting exciting now. We got the engine fired up last Sunday (it’s on Speeduino with Triumph bike ITBs) This showed up a few issues including a non-functional clutch.

Had another day on it yesterday (pity he’s 100kms away) and have resolved all issues but the clutch.

Copy of my last post on the above linked thread - in the hope that someone can magic a solution that doesn’t involve pulling it all to bits again…. (Yep, fat chance I know, but still)

As I mentioned before, we previously had a clutch which passed the “roll in gear without turning the engine” test, albeit with the pedal near the floor. This didn’t allow the engagement of gears though. The 0.625 m/c was suspect, so got a good clean out and rebuild. A thorough bleeding seemed to improve the pedal feel and raise the biting point (determined by the roll test), albeit still below mid-travel, but it remained impossible to engage a gear with the engine running. It was possible to start the car in gear but it was tugging quite hard and would not release further.

Frustrated, we tried a 0.7” m/c. The effect of this was to raise the biting point (determined by roll test) to well above mid travel, but no improvement on ability to engage gears with the engine running, and it tugs just as hard if started in gear and the rate of “tug” increases with revs.

Bollocks!!  But why?

It's the OE Ford flywheel with OE (Sachs, used but apparently good) clutch cover. Friction plate is Mazda of similar diameter and thickness to the Ford one. It’s had (quite radical) reduction surgery to the splined boss to prevent contact with nose of the concentric slave cylinder (the issue I had on my GT6).

Pilot bearing is an oilite bush (tight in crank, running clearance on the input shaft. We’ve checked there is still end float on the crank.

Slave cylinder is the Omega CSC as used on my GT6 MX5 gearbox conversion. Possibly the thrust bearing is a bit big for the profile of the diaphragm fingers (I’ve not seen it myself) so there could be some motion lost here, but increasing the hydraulic travel raised the apparent biting point by about what I would have expected so….?

No strange noises. No “sensation” fed back through the pedal. Pedal feel is very light, even with the 0.7 m/c. Perhaps a little “mushy” at the top of travel and no obvious feel of it going over-centre.

So WTF is wrong with it? Seems we (he) is faced with the taking it apart again - unless anyone has any bright ideas. I have a (short) list of suspects but would very much like more suggestions!

To add that we are pretty confident of the bell housing alignment re. parallel and concentricity and I’m told the box goes all the way onto the engine easily.

[mjrstar]

How much clearance on the pilot bearing(bush)?

How close is the friction plate thickness to that which would be matched to the pressure plate?

Is the concentric slave designed to be a constant contact, and if so is the spring weight appropriate?

 

Come to think about it, I had a similar problem with the metro turbo clutch in my mini, I managed to start it in gear and then a couple of clutch dumps and it came good. 

Almost like the synchros were dry and the slightest bit of drag meant you couldn't select a gear.

[Unclejake]

11 hours ago, VitesseEFI said:

This showed up a few issues including a non-functional clutch.

 

Non-functional as in he can't get the clutch to release, or non-functional as no drive is transmitting from the engine to the road wheels?

[VitesseEFI]

Releases enough to roll the car in 4th gear easily, but not enough to get it into gear with the engine running.

[gibbon]

Can you adjust out the clutch pedal pushrod to try and get a little more throw on it? I guess you don't want the bite point too much higher though 

[R3spct]

So im going with Gibbon, it sounds like the clutch pedal rod to cylinder needs to be longer, so it disengages more and raises the pickup point.  If its not that, then something is dragging or binding or going over center and binding? 

Exedy used to do a "heavy duty" kit for fwd sr20 that needed a shorter clutch throw to disengage, stock nissan pedal setup would over throw it, causing the springs on the clutch plate to hit the fingers of the pressure plate and eventually smash them out and then all sorts would go wrong. Of course exedy would never warranty it despite no documentation being provided with the kit to explain the necessity. 

[mjrstar]

The other thing with a concentric slave is they can be a little tricky to 100% bleed, but if you have a known engagement point at mid stroke it seems unlikely that it actually needs more hydraulic travel, well unless the master cylinder or pedal ratio is miles undersized.

 

Also spent quite some time finessing the excedy hyper single in my honda. The adjustment was a little unconventional including a fork pivot mod, master cylinder spacer,  and up and down stops. Due to too much hydraulic travel.

[Unclejake]

I'd remove the gearbox and pay VERY careful attention to the gearbox input shaft nose and how much fore and aft clearance it has to the crankshaft when the bellhousing is bolted up tight to the engine block.

[VitesseEFI]

18 hours ago, mjrstar said:

Come to think about it, I had a similar problem with the metro turbo clutch in my mini, I managed to start it in gear and then a couple of clutch dumps and it came good. 

Yeah…. If the engine wasn’t freshly built and completely un-mapped….. and his road want steeply sloping and fairly busy…… I might have been tempted to try to drive it…. Perhaps advancing age and dodgy experiences are bringing wisdom /caution /cowardice (you choose!)

6 hours ago, mjrstar said:

The other thing with a concentric slave is they can be a little tricky to 100% bleed, but if you have a known engagement point at mid stroke it seems unlikely that it actually needs more hydraulic travel, well unless the master cylinder or pedal ratio is miles undersized.

Yes, all of this.
 

One possibility though is that the diaphragm fingers are shaped to give a raised landing area for the release bearing. I’ve not personally had the change to view them together but eyeballing the spare pressure plate, I have concerns that our bearing might be a bit big for the landing zone, so there might be a bit of a ‘rolling down a cone” effect robbing some motion but I still feel the bigger m/c should have overcome that - unless it’s causing the pressure plate to tip.

My other thought is simply that when he’s shortened the splined boss in the friction plate he’s not de-burred it well enough after, and it’s just hanging against the flywheel….. which would at least be and easy fix - bar all the dismantling and reassembly….

[VitesseEFI]

So, to update you, it’s all apart again.

At least two problems….

This is the scarier one. As assembled, the oilite spigot bush was an interference fit in the back of the crank and a nice running fit on the input shaft. Though apparently not at the same time…. No specific measurements were made to determine the degree of crush inflicted by fitting to the crank nor was a test fit without clutch done. I would have done these things. My son was not (yet) that paranoid. He is now!  He merely noted that the gearbox “went on pretty easily”.

Input shaft is heat marked but not really hurt. Bush picked up on it and spun in the crank. You can just about see a small step on the right which is the original OD (21mm) vs. the “self clearanced” which is about 20.75, perhaps tapering very slightly to the left but no more than 0.05.  Lots of oil came out of the bush. This self-adjustment can only have occurred during the “started in gear” periods, which amounts to less than 60s run time. I’m struggling to reconcile this with the “gearbox went on easy”!  More investigation needed here for sure….

The other issues (actually two related) is that the friction plate used (8.6mm uncompressed) is a bit thicker than his original test one (8.1mm, matching the OE Ford one) and apparently slightly too much for it as it significantly increases the release distance. Might have got away with it except the over-stroking from the bigger m/c crashed the back of the diaphragm fingers to the cushioning springs.

Surprised we didn’t hear that!  This is fairly easy to sort as his original test friction plate is now proven to release well within the stroke of the smaller m/c (which is originally tested) and has the springs further out.

Development and learning curve….

 

 

[RUNAMUCK]

Using a mish mash of parts once, i unknowingly used a clutch with an ever so slightly raised boss on the inside of the centre hub. And while it sat nicely inside the recessed centre of the flywheel, the outside edge just touched against the capscrews id used to affix the flywheel to the crank. (Due to the taller heads) this meant that i never enjoyed 100% clamping force. And despite a 36% increase in friction surface area, it was still prone to slipped under maximum abuse. (Every single time i drove the car)

[mjrstar]

I'll fax through the invoice for 1x chocolate fish.

[VitesseEFI]

2 hours ago, mjrstar said:

I'll fax through the invoice for 1x chocolate fish

But yes, you were right on the money querying the pilot bearing clearances….

Wish I knew whether it’s purely a clearance thing or if we’re dealing with some misalignment as well.

There'll be a gap in progress now as he’s gone on hols and when he comes back I’m off to drive around some of Europe’s hillier parts in another old British car with a dodgy gearbox conversion…… This one’s done 50k miles or so though and can be considered semi-proven.