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Author: Subject: St170 to Mazda rx8 gearbox.
Pigsy

posted on 23/5/19 at 11:52 PM Reply With Quote
St170 to Mazda rx8 gearbox.

Hello everyone. I have mated an st170 to an rx8 6speed box. St flywheel. Ford transit heavy duty clutch complete. Rx8 slave cylinder and thrust bearing and pivot lever/arm. 10mm adapter plate.

Iím getting problems getting in to gear. I understand the problem of needing a longer slave pusher ďpinĒ. I made one 10mm longer to make up for the adapter plate thickness.

Has anyone any useful suggestions as I donít want to pull the engine and box again. Itís a lot of work in the mgb gt that Iíve put it in. Only just fits.

Thanks ĒPigsyĒ.

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Nickp

posted on 24/5/19 at 07:43 AM Reply With Quote
Are you getting full travel of the slave cylinder?
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Pigsy

posted on 24/5/19 at 09:05 AM Reply With Quote
Yes I believe I am. Itís a new slave cylinder and itís bled well.
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big_wasa

posted on 24/5/19 at 09:52 AM Reply With Quote
Nobody uses the St dual mass flywheel, it's a very heavy piece of scrap.
They are a lot thicker than a solid flywheel. You may be over compensating if your bassing it on what others have done with a solid flywheel.
Have you used the transit cover plate or the st ? The st won't take the cush drive off a conventional clutch.

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Pigsy

posted on 24/5/19 at 04:14 PM Reply With Quote
Hi. I did use the dual mass. It was recommended by quite a few people who had problems with the single mass flywheel. Ho hum. The clutch was complete and had the cover. Iím using the Rx8 thrust bearing. The clutch was very much like the st170 set but had the different spline count. I donít know the Rx8 cover depth.
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CosKev3

posted on 24/5/19 at 04:16 PM Reply With Quote
Does the input shaft reach to the spigot bearing?

Presuming you've fitted a spigot bearing for RWD set up?

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Pigsy

posted on 24/5/19 at 04:33 PM Reply With Quote
Prompt reply thanks. I believe it does. There are no unusual sounds or vibrations coming from that area. I had the car on stands until yesterday evening and could run it and once in gear to start it. Interestingly, I could with difficulty change gear to second using the clutch pedal. It wonít go into gear with the clutch depressed and just crunches cogs. It just did not push the pivot arm enough to get it in gear or for a good change. I have lengthened the slave cylinder arm this afternoon, but just too much and itís not in the car yet.

Iím chasing the receipt from the clutch and cover plate. I want to be sure of what Iím saying regarding what it goes into.

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Pigsy

posted on 24/5/19 at 04:38 PM Reply With Quote
Sorry but what did you mean by: The st won't take the cush drive off a conventional clutch.
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big_wasa

posted on 24/5/19 at 04:59 PM Reply With Quote
The st uses a dual mass flywheel and a solid clutch plate. Conventional clutches would have springs to cushion the drive line and a solid flywheel. This hub of springs and rubber has to fit in the cover plate or sometimes the flywheel. If this is the wrong way around or in a cover plate that doesnít clear, you wonít be able to depress the clutch properly. But I donít know the clutch you have used.

I still havenít heard of anyone picking an St fly over a solid one. Any ideas why ?

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Pigsy

posted on 24/5/19 at 05:22 PM Reply With Quote
A local mechanic with and st converted had this problem: The new flywheel had a very slight vibration. He took it for a ride and while revving the engine it smashed throught the side of the block, smashed the bellhousing to pieces, smashed the rad and dented the bonnet. It shattered in 2 sections. Could have been faulty but it was too damaged to tell. It was a lightweight but not cheap. He tunes stís. Has happened to him more than once but not this seriously.
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rusty nuts

posted on 24/5/19 at 05:46 PM Reply With Quote
Was he using a flywheel that had been lightened or was it a lightweight steel flywheel? In suspect your lever pivot maybe too short , a longer one would bring the thrust bearing closer to the cover ? Think you would have to measure the clearance you have at the moment?
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CosKev3

posted on 24/5/19 at 07:08 PM Reply With Quote
quote:
Originally posted by Pigsy
Prompt reply thanks. I believe it does. There are no unusual sounds or vibrations coming from that area. I had the car on stands until yesterday evening and could run it and once in gear to start it. Interestingly, I could with difficulty change gear to second using the clutch pedal. It wonít go into gear with the clutch depressed and just crunches cogs. It just did not push the pivot arm enough to get it in gear or for a good change. I have lengthened the slave cylinder arm this afternoon, but just too much and itís not in the car yet.

Iím chasing the receipt from the clutch and cover plate. I want to be sure of what Iím saying regarding what it goes into.


You believe it does have a spigot bearing?

Pretty sure you would have had to add one when you converted it?

Good point about the clutch plates above,dual mass flywheel use a unsprung clutch plate,solid flywheels use a spring plate,they ate not interchangeable

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big_wasa

posted on 24/5/19 at 07:50 PM Reply With Quote
St comes from the factory with a spigot bearing.
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Pigsy

posted on 24/5/19 at 10:14 PM Reply With Quote
I believe that the splined lay shaft that the clutch slides on goes into the spigot bearing. It has a spigot bearing. I would not have left it out.
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Pigsy

posted on 24/5/19 at 10:26 PM Reply With Quote
The flywheel came from a company selling lightened steel flywheels. Don't ask me who.

The clutch cover was a Ford Focus Transit 1.8 Borg & Beck. The plate was an MGB 1800 BORG AND BECK HEAVY DUTY CLUTCH.
The cover fitted the flywheel as it should. The plate was the right size and thickness.

I have lengthened the slave push rod by 13mm. 5mm to make up for the adapter plate and 8mm to take the slack with the push rod seated deep in the slave cylinder. I will try it tomorrow and let you all know.

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Pigsy

posted on 24/5/19 at 10:31 PM Reply With Quote
The lever pivot is the standard rx8 item as used with this gearbox. It fits well.
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CosKev3

posted on 25/5/19 at 08:31 AM Reply With Quote
quote:
Originally posted by Pigsy
I believe that the splined lay shaft that the clutch slides on goes into the spigot bearing. It has a spigot bearing. I would not have left it out.


Does the shaft reach the spigot ok though once the 10mm adapter plate is added?

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big_wasa

posted on 25/5/19 at 09:00 AM Reply With Quote
Iíve never heard of one of the reputable steel flywheels exploding ie Ttv, Turbosport, Raceline.

I have seen some pretty scary looking lightened cast flywheels.

But if you where worried an Oem Zetec flywheel would be a better start than an St170 flywheel. They where so crap that you where lucky if one lasted three years and the clutch couldnít cope with a standard St so was changed half way through itís life and upped from 230mm to 240mm. In cars with more torque like a diesel Mondeo they chewed through the flywheels even quicker with the debris taking out the csc and the starter at the same time.

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Pigsy

posted on 25/5/19 at 11:08 AM Reply With Quote
Thanks for that, but, as it's all fitted and in the car I will leave it there. Hindsight is the only exact science and at the moment if it comes to it, then i will do it. You no doubt have a wealth of knowledge that is far greater than mine.

By the way, its not my first engine swap, Ive done many on Morris minors, cortina's, escorts and the like. Its the first new school with a modern ecu, electronic ignition, itb's etc

Im in my 60's and not well at all. i"m struggling but wont give in. its taken 2 years so far. A couple of decades ago it was a months work. Ho hum.

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Pigsy

posted on 25/5/19 at 11:14 AM Reply With Quote
Does the shaft reach the spigot ok though once the 10mm adapter plate is added?

Adapter plate is actually 6mm.

As I said, I believe it does. I measured before hand and I have no vibrations or wobbling when the gear is engaged and everything is turning over at high rpm with the wheels of the ground. I have no problems with the spigot shaft. Take it as engaged. The problem is i'm sure the slave cylinder and pivot arm length. Im hoping to know this afternoon.

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Pigsy

posted on 25/5/19 at 11:16 AM Reply With Quote
I have lengthened the slave push rod by 13mm. 5mm to make up for the adapter plate and 8mm to take the slack with the push rod seated deep in the slave cylinder. I will try it and let you all know.

Please read the threads. I appreciate the help but please see what is written first.

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CosKev3

posted on 25/5/19 at 11:24 AM Reply With Quote
I'm out,help yourself!
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Pigsy

posted on 25/5/19 at 02:40 PM Reply With Quote
Thanks. If anyone else is listening, the slave cylinder is not getting full travel from completely compressed. Itís the clutch master not pushing enough.
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big_wasa

posted on 25/5/19 at 04:46 PM Reply With Quote
If your not getting enough travel at full stroke the option is to change master to slave ratio. Ie one or both with a bigger or smaller bore.


I am not telling you I know better or I know everything. I am just sharing my opinion and research and experience on the St flywheel and clutch combo.

The combination you have put together is pretty unique.

[Edited on 25/5/19 by big_wasa]

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Pigsy

posted on 25/5/19 at 05:23 PM Reply With Quote
Thanks so much for the reply. I appreciate it very much. The mgb clutch master is an 18mm bore with a 25mm throw. I noticed this on eBay: Tilton 74 Series Universal Brake / Clutch Master Cylinder 1 1/8" Bore Size. The bigger bore will make for a very stiff pedal I expect but I can live with that. The extra throw will be good. I think that there is another 6mm travel in the slave cylinder. I hope Iím right.

I have no problem with any suggestions. I was just being asked the same questions repeatedly and being told of for using a dual mass flywheel.

I appreciate your genuine help. I will just be happy if it works reasonably well

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