Will this gearbox fit my Marlin?

[Robert in Cumbria]

I have found a Triumph Dolomite gearbox today which is said to be in GWO. It has an overdrive, Clutch housing and output UJ flange.

My Marlin has a Marina 'A' series 1275 engine complete with it's original gearbox. Will this gearbox fit my Clutch housing with or without machining or mods? I have access to lathe and a vertical/horizontal Milling machine (and large hammer!).

This question may have been raised before but my expertise at searching is limited so please accept my apologies if this has been asked many times before!

I found this image on the Rimmers site, and have 'borrowed it' for educational purposes. This is the underside which I have not seen before but it looks generally the same. I think it has what is termed a single rail gear selector shaft. There is a single rod in a tube from the top of the G/B back to the gear lever.

It has various switches screwed into the casting and the speedo drive is present.

[b_caswell]

Re: Will this gearbox fit my Marlin?

Robert, That is a Single rail gear box with J type O/D But it will depend on which Dolomite its from ? If its from a 1500 its a NO the input shaft is too short for the Marina bell housing ----- but the 1850 is a Yes with a Marina bell housing although there is some concern that the input shaft splines are slightly shorter this conversion has been done by quite a few people without problems.You will need the Triumph clutch plate.

The other way to do it is to change the mainshaft in your Marina box and use the dolly o/d mainshaft then bolt the O/D to that box. MOC tech tips tells you all you need to know.

[christopher.bogue2011]

Re: Will this gearbox fit my Marlin?

Hi Robert,

I went down this road with my Marlin years ago. I used the 1850 gearbox as the first motion shaft from what I can remember was the same as the Marina's. All I did was to bolt the Marina Bellhousing onto the 1850 gearbox. I had to modify the gearbox mount and slightly re-jig the tunnel along with shortening the prop shaft but all was very straight forward and I am not an engineer by any means.
Regards,
Chris

[Robert in Cumbria]

Re: Will this gearbox fit my Marlin?

Thank you both, I will get the box and sort the details later, one way or another it seems I can use it. I will check out the numbers, there is a card tag tied to the O/D with string, it has numbers on so it may be a recon unit, the numbers are very hard to read but may mean something so I will try to decipher.

How can I identify the 1500/1850 differences from appearance please? I will post photo's of the box later.

Are the shaft lengths 'known'? If possible front face of G/B to tip of spigot would be very helpful.

I take it the 1st motion shaft and lay gear are different from the 1500 set?

I know or knew all this stuff on Mini's, this is another batch of data to learn. All great fun!

[stevejgreen]

Re: Will this gearbox fit my Marlin?

Lots of info on these Dolomite Gearboxes is in the Tech Tips and archived Pitstops.

Different input shaft dimensions below.

[tony.branson76]

Re: Will this gearbox fit my Marlin?

Hi Robert,
Fred Mills who you met last month has an overdrive gear box in his B series engined marlin. I don't know what it came from. With the B series the first motion shaft has a larger diameter. I know it has the standard B series shaft as I helped him change the clutch and that's a saga on its own ( the rear engine mounting was fitted after the engine and welded in place). Fred may have some information and you could have a look at his fitting. I'm sure you will be able to fit it it will require a shortened prop-shaft but that's not too difficult.
Cheers

Tony

[Robert in Cumbria]

Re: Will this gearbox fit my Marlin?

Well I bought it... The price went up £10 overnight but I beat him back down!

It is a Dolomite 1850DL Gearbox it appears, the serial is WM-2000, apparently from my research WM denotes an 1850DL gearbox.

The input shaft (1st motion shaft) has 19 teeth and is as shown on the left of Steve's diagram.

I have cleaned it up and drained it, there was a little gunge stuck to the magnet but no big lumps, the baulk rings seem OK, there is a bit of slop in the selectors but I will see what the original gearbox is like if/when it clears the V5 inspection. All the gears seem to select OK and they seem smooth enough. There is no gear lever with it but I will cobble something up.

[b_caswell]

Re: Will this gearbox fit my Marlin?

Thats looking good but a recount on the splines should be 20. Dont loose those 3 little springs that load the lay shaft and that bottom bolt is the one to remember with the copper washer.

[Robert in Cumbria]

Re: Will this gearbox fit my Marlin?

The TEETH on the 1st motion shaft, not the splines! I mentioned it because some of the ratios in different boxes vary, I have seen that somewhere but despite much searching I can't find the tooth counts again.

Does anybody know what the standard 1300 Marina clutch plate Dia is please, I don't seem to be able to find that either. I need an equivalent Triumph driven clutch plate to fit the input shaft. Unless I can swap a Triumph spline hub for a Marina spline hub. I did that years ago to fit an Escort gearbox on an Anglia engine. We even managed to get the correct rivets from Ford! I still have three because they gave us six (Yes GAVE us) just to be sure in case we messed up with the first attempt.

It needs a new copper washer! and perhaps better sealant in the threads of the bottom bolt. It had oozed quite a bit of oil from that location. I have re-fitted the Dolomite clutch housing to preserve the springs and keep dirt and sand out of the front bearing. I live barely 100 yds from the shore and sometime the air is full of sand dust when the wind blows from the estuary if the sand is dry.

Digging through the boxes of bits last night I found a gear lever which looks as though it will fit.

[tony.branson76]

Re: Will this gearbox fit my Marlin?

Hi Robert,
I have an A -series clutch somewhere on the mezzanine floor of my garage and also a 1300 marina gearbox. That came out of my original Marlin before I fitted Jonathan's B series engine and gearbox which he lent me. I have returned the engine to Jonathan but the gear box lost all the crinkly bits on first gear on Bamford Clough ( I think the sequence of events was me landing back in the car with my foot on the loud pedal shortly before the rear wheels landed on the ground). I'll see if I can find the clutch and measure it. I assume it's the diameter overall and the spline numbers that you need.

Cheers

Tony

[Robert in Cumbria]

Re: Will this gearbox fit my Marlin?

Hi Tony,

Yes the OD of the clutch is my main interest right now although eventually I will be able to access my own, once the V5 replacement is resolved one way or the other. It's very frustrating not being able to touch the car until it's been inspected.

You don't have a Marina 'A' series block too do you? I desperately want to weld in the engine mountings before the weather turns on me, but I need a Marina block to locate the positions. I have Mini blocks but they don't have the same mountings. The hybrid chassis had Ford mounts which I removed but no trace of any 'A' Series mounts.

I do wonder if taking 3mm off the back and front of the clutch housing (total 6mm) would help the engagement of the clutch plate splines to regain half the missing 12mm and probably achieve full engagement of the splines. But pulling the box shouldn't be too big a job even if it did drag slightly, I don't see this car doing a big milage. I am planning to be able to access the gearbox from inside the car, so removal should be easy.

[b_caswell]

Re: Will this gearbox fit my Marlin?

Hi Robert, I am not sure if these figs help but I have a single rail box from a 1500 Spitfire stripped at the moment and have counted the teeth.

input-- 16t/ Main shaft 3rd 20t/ 2nd 25t /and 1st 29t

lay gear front/input 29t/ 3rd 26t/2nd 21t/ 1st 15t

this gives gearbox ratios Top 1:1/ 3rd 1.39:1/2nd 2.16:1/1st 3.99:1

It seems the smaller engine Triumphs do use lower ratios but they also use

the box that uses the short input shaft which isnt suitable for the Marina.

If you do mill the faces of the bell housing you will need to watch the clearance between nose of input shaft and inside of the crank end.

[stevejgreen]

Re: Will this gearbox fit my Marlin?

As far as I know there were three different clutch sizes fitted to Marina / Ital cars.
Very early 1970-71 1.3 Marinas had a 20 spline 165mm / 6.5" dia plate, These were changed as they were found to be under sized.
Later 1.3 Marinas & Itals had 20 spline 184mm / 7.25" dia plate
All 1.8 Marinas and 1.7 Itals had 23 spline 203mm / 8" dia plate

The saving grace is that generally Triumph gearsets are much more available than Marina. So if the clutch splines do wear prematurely replacement input shafts should be available.

[Robert in Cumbria]

Re: Will this gearbox fit my Marlin?

Thank you both,

Ben, The 1500 ratios are interesting, I will compare them with the 1850 when I have a moment. I was anticipating cutting ~ 6mm off the spigot. I once fitted a manual gearbox to a previously auto Rover V8, I didn't realise auto spigot bearing was steel, a very noisy screech with the clutch held down! I had to drop the engine back out and swap a bronze spigot bearing out. What might be more of an issue is machining the recess for the first motion shaft bearing and clutch release bearing sleeve 3mm deeper. I will weigh it up when I get there. On balance I don't think the larger 25mm shaft with 23 splines will suffer too much punishment from an untuned 1275 engine.

Steve, I have seen some listings stating that the 1.3 Marina has an 8 inch clutch plate with the 22mm 20 spline drive, although I don't question your post. Rather my source, which was why I asked the question. Perhaps Tony will come back with a measurement once he finds his clutch plate.

I am counting my lucky stars with this find, we were actually looking for a part for Lee, it was my 11 year old son who spotted it and said "Dad... isn't that a Triumph gearbox lying in all that junk, what's that extra bit at the back?" Hang on... Since when did Michael know what a Triumph gearbox looked like! I must be training him well! I explained what the "extra bit" (the overdrive) did and why. He sit's and reads workshop manuals in spare moments.

[stevejgreen]

Re: Will this gearbox fit my Marlin?

Your idea of thinning the bell housing down, starts off looking good but....
The weight of the Triumph box, prompted the BL engineers to add an extra plate between sump and bell housing.
On the engine face of the bell housing you have very little meat where the bolts run through into the block. Similarly at the gearbox face you would have to bore the recess for the 1st motion shaft sleeve that the thrust bearing runs on. You would also end up with a very shallow hole for the clutch arm pivot pin to mount in.
I think it all becomes rather too marginal to be practical.


There are loads of odd dimensions quoted for Marina clutch plates. I have seen one, I think Borg Beck, that quoted 215mm / 8 1/2" Dia but what will actually fit inside a 1.3 or a 1.8 flywheel/clutch assembly is anyones guess unless you have both to measure.
Another variation is that despite identical bell housings, the 1.3 and 1.8 thrust bearing carriers are different overall lengths, presumably to cope with different flywheel thicknesses.

I think that most of the data in Tech Tips is based on 1.8 engined cars, and just where the clutch splines actually engage might be better, assuming the 1.3 flywheel is thicker of the two.

Sorry if I am rambling, but thinking as I type, and I will have to rummage in the garage to see what parts I have to measure.