Dan Lockwood

Good morning everyone. I'm new here so this is my first thread topic.

I've tried other Miata forums, but none have responded. I joined this forum back in '15, but life got in my way of this awesome new project and it's now back on track.

My question will be better at the end after you all have the background on my build project.

I'm going to be building an open wheeled car powered with a Harley counterbalanced Twin-Cam "B" motor. It will be coupled via an adapter that's used in the manufacture of the new Morgan Three Wheeler in the UK. They have the adapter between the motor primary bolt pattern and the bell housing of the Miata 5 speed. There is an inset plate in the adapter that has a double row sealed bearing that supports a stub shaft with the flywheel bolt pattern. Inside the adapter is a coupling of sorts. They originally used an actual Harley compensator, but they wore out really quickly. Now they use a Centa rubber coupling that allows for around 5 to 10 degrees of wind up to "compensate" for the torque pulses of the Harley motor. Without the soft coupling the trans would get really beat up.

Here is the Morgan M3W with an S&S 2L motor with the drive arrangement explained above.

Actually this is close to what I was originally going to build.



Then someone on Talk Morgan did a little Photoshop on the M3W and came up with the M4W. WOW, what a great looking little beast... Well that's my opinion anyway.



I'm going to be adding suicide doors and will have more of a hotrod tubing main frame than Morgan's space age tube chassis. So I'll be running my exhaust under the body along the outside of the main frame rails. It will be exposed, but not in any way to get burned on. It also gives access for the doors.

I'm going to be using a MG Midget rear axle housing stretched about 3" to 4" per side to give me my rear wheel track I need.

Here are a few pics of the Morgan drive line.

Here's the motor with adapter and trans. This is a Miata 5 speed.




Here's an out of focus but better picture of the adapter area. The groove cut into the top is for the rack and pinion center section.



One last pic of the trans.



So with my build and running a 3.9:1 rear axle ratio and 18" wheels/tires, I'm thinking that the 6 speed would be a better choice for me and it also picks me up a little bit more on the first gear and then better gear spacing.

I "think" that Morgan uses new '06-'14 Miata 5 speeds. Is that what's shown in the pictures above?

They do NOT run the Miata flywheel and clutch, but they use a Volvo light weight setup and I believe Volvo's hydraulic throwout bearing assembly.

I plan on using the stock Miata clutch slave cylinder setup.

So here's my question. If this is a '06-'14 5 speed, which, if any, 6 speed will have the same bolt pattern? Are certain 5 speeds and 6 speeds interchangeable?

Because I'm going to be purchasing the Morgan adapter, Centa and the stub shaft assembly, I'm really locked into the Miata trans setup. Morgan has had LOTS of issues with their M3W's, but the Miata 5 speed has not been one of them. They seem to be holding up amazingly well.

If I want to go to the 6 speed, which I'm thinking I do, what year 6 speed would be a bolt in replacement for the 5 speed pictured above?

I've seen on eBay quite a few light weight flywheel sets and some aluminium flywheel sets. Are there any better than other sets that I might look at? I'm going to be running around 80 to 90 hp when completed. I need to keep it all as light as possible as the Centa compensator weighs quite a bit.

I greatly appreciate whatever information I might be able to get.

Thanks in advance.

Dan

See Dan's Photo Albums

Midtenn

iTrader: (15)

The tail shaft housing on the transmission isn't from a NA/NB (89-05), so its likely NC (06-15) if its from a Miata. In that case, you'll just need to find a 6 speed from the same year range. They use the same bolt pattern and PPF mounting.

This calculator might help you visualize the speed and gear ratio differences: Gearing Calculator - Graf Garage

Dan Lockwood

Midtenn, Thanks for the reply.

So as long as I stay year series to year series, 5spd to 6spd, I should be okay in swapping out to the 6spd. Thanks.

What about light weight flywheel sets? Are there some reasonably prices assemblies that I should look at or stay away from?

I have a Morgan stub flywheel shaft from the very early Harley compensator type coupling. Is there a bolt pattern available for say an '06 or so Miata crankshaft that I can compare to what I have? Because Morgan uses the Volvo flywheel/clutch assembly, I would like to make sure the adapter I buy will have the correct bolt patter for the Miata. If they are Volvo and not compatible with the Miata, I may have to draw one up here at work and have it made on our Mazak turning center to match the Miata.

Thanks again and look forward to sharing my project.

Dan

Monk

iTrader: (3)

Midten is right. That is an NC 5 speed.
The 6 speed from that generation is a monster by comparison.

Dan Lockwood

Monk, thanks.

I can probably get by with the 5 speed and it's low gear, but having the steeper low of the 6 speed could be a help.

So from what you guys are saying, the 6 speed will bolt to the same motor and use the same clutch/flywheel assembly, but takes up WAY more real estate and would harder to build around? I would imagine that the foot well and pedal area would have to be sacrificed a bit to make room for the larger wider 6 speed.

Just thought I'd mention it again, does anyone have the crank/flywheel bolt pattern for the Miata of this vintage? I need to compare what I have with known accurate flywheel dimensions.

I appreciate all of the views and I'm getting good information, thanks a bunch...

Dan

Monk

iTrader: (3)

I'm having a hard time tracking that down, and I don't have one to measure.
Don't take this screenshot as gospel, but check it against what you have:

Dan Lockwood

Monk, that is awesome.... THANKS.

I'll check it out tonight when I get home.

curly

iTrader: (25)

Are you using the Morgan frame? If so you have near zero room for a larger transmission. As for the clutch/flywheel, only the throw out bearing is Volvo, the flywheel is a custom billet piece, mated to a 7" racing clutch, most likely Tilton or similar. No markings on the one I'm currently looking at. Please ignore my lunch.

If you have any questions, feel free to ask me, I've worked on a them quite a bit, this clutch/flywheel is out one that's getting it's engine replaced. Again.

ryansmoneypit

iTrader: (6)

I got to drive a Morgan, the very early one using the Harley / VW transaxle. man what fun it was!

Dan Lockwood

Curly, thanks for the picture and information.

I've seen several on the Talk Morgan forum while they were down for the compensator/Centa upgrades. I didn't recognize the flywheel when I saw it and they said that they got parts from Volvo, so I figured they might be Volvo parts.

I plan on building my frame from 2"x3" tubing and doing it similarly to a hotrod frame. I have some very heavy a-arms from an ATV/Quad that I'm in the process of converting to my needs. The M3W uses London Taxi ball joints that screw into the spindle top/bottom and then the taper goes into the a-arms, just the opposite of most ball joint applications. I have purchase four London Taxi ball joints from a UK vendor of taxi parts. They cost me almost as much for shipping as the parts.

I plan on making my own front axles and they will be pressed and welded into the heavy wall spindle tubing just like the M3W uses. I like the clean look and the tall spread between the ball joints; very old style looking. I have a Mustang II polished rack for the steering and am still working in AutoCAD on the front geometry to get rid of the potential bump steer. I'll be using Triumph Spitfire drilled and slotted front rotor and Wilwood 4-piston calipers. The splined wire wheel hubs will be MG/Sprite short style. I'm be buying all the wire wheels from the UK to match my hubs. I'll be running the exhaust along the bottom of the body but under so no one will get burned on them.

I think I'm going with quarter elliptic rear springs mounted outboard the body for looks and better control of roll. I think I'll stick with stock rear drums, but all new. They MG guys say they have more than enough stopping power on their track cars, so that's good enough recommendation for me.

I guess I could fit in the 6 speed as I have no foot well limits, within reason that is. I like the lower 1st gear and I'll be running a 3.9:1 open rear end.

On the M3W, where do they put the starter? I don't see them mounted in the opening on the trans bell housing.

So if I were to purchase an aluminum flywheel and use a spring center hub mild race clutch disc and pressure plate, I'm sure that would be enough for my needs.

I'm glad you shared your experience about the Morgans.

Thanks again and have a great evening.

Dan

curly

iTrader: (25)

Uses two bolts from the side. As you're finding out, nothing comes from the same car, so I'm not sure where the starter comes from.

Dan Lockwood

Curly, can you post a picture or two of the starter? Maybe starter tags or numbers etc?

Where the adapter is machined out, is that the "normal" location of a Miata starter?

Can you purchase parts through Morgan? I've had some quotes from Norb up in north Chicago on the adapter, Centa and misc parts. If pricing is the same, I'd rather buy from someone I know.

I confirmed, not that there was any doubt on your end, but from the chart that Monk posted, my old Harley compensator stub flywheel shaft has the 2.75" bolt patter and 1.261" center protrusion to center the flywheel. There is no dowel pin hole though. This is the one with the splined shaft and the new Centa stub flywheel shafts just have a single key with a bolt in the middle to hold it all together.

One of the forum guys in Europe added a machined center shaft on the Centa inner shaft assembly and then machined a matching bushing that goes inside the motor outer housing. When installed, the shaft goes into the bushing and stabilizes the inner shaft assembly from wobbling on the end nearest the motor. He said that it did help vibration a bit. He's also designed and hand cut urethane elliptical pucks to replace the rubber rods in the Centa. There seems to be a LOT of guys right now that the rubber rods have broken up and falling out. One guy only had one rubber rod intact and he noticed a bit more vibration and tore his apart and found them in chunks and some missing. Also the elliptical pucks limit the wind up between the motor and trans. The Harley compensator would allow around 10 degrees of wind up on the torque pulses. The stock Centa was close to the same in degrees of wind up. The guy in Europe said that with the elliptical pucks he can take off in 1st without any throttle and no lugging or shutter in the driveline. Makes one wonder. But the purpose it so isolate the crank torque pulses of the Harley from beating up the trans.

I appreciate your help and sharing of information.

I've got a LOT of work ahead of me on this project, but it will be fun and should be a great looker when I'm done.

Thanks and have a great day.

Dan

Dan Lockwood

Curly, is this what the starter looks like? If so, as you probably know it's a Miata. But you being familiar with Miata's and you saying that you didn't know where it came from, I doubt this is it, but worth a try anyway.


Thanks and have a great week.

Dan

curly

iTrader: (25)

Dan Lockwood

Curly, not sure if it's too late or not, but the adaptor/housing for the Centa compensator, how long is it?

That would be a big help on my AutoCAD layout. I've only been able to guess to this point.

Thanks and have a great weekend.

curly

iTrader: (25)

I can get a measurement for you possibly Sunday if I remember, if not Monday. About to install another engine in one as soon as some parts arrive.

Dan Lockwood

That sounds great, thanks.

curly

iTrader: (25)

As close as I can tell, engine to where the trans bell housing would bolt up is 10 7/16".

Dan Lockwood