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R Cubed

GMC 352 Engine Conversion

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Hi all well here we go, some of you might have heard about this when it was over in france last year. Well if not here we go.

This thread will detail how I have fitted a Cummins 6BT and ZF s5-42 gearbox out of a Leyland DAF 10ton tipper into my GMC 352, having had the truck for many years I have got fed up with the fuel costs, so when this engine and box came up for sale I thought it would be an ideal engine swap !!! Some said it could not be done, but I have done it and also covered roughly 700 miles fuel consumption is well under half of what I was doing..

 

First step remove cab and old engine and gearbox to get to chassis rails and see what I have to play with.

 

here we have removed the cab complete which is heavy as some of you will know.

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This is what we used for cab and engine moving high enough to get the pieces over the front of the rear body.

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Now time to get the old engine and box out we did the same thing as the lifting frame is stationary we had to move the truck about.

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Edited by R Cubed

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Once the cab and old engine and box are out you are left with all the bits and bobs which are attached to the chassis rails under the cab such as the Hydrovac and brackets, brake master cylinder and bracket, high, low / front axle leavers and bracket, gearbox mounts very quickly it dawned that this is a much longer engine and box than what had just come out !

 

So all above items had to come off, some of these do not just unbolt they are hot riveted so what I did with these items so as to be reversable all I did was to drill out the rivets.

 

The other stroke of luck came by the way of the starter motor being on the same side a the GMC engine this meant that is was out of the way of the steering box a major bonus, phew.

 

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As you can see the high low bracket was well in the way, just infront of these leavers would be the gearbox mounts which would be hot riveted to the chassis these have already been drilled out and removed as the bellhousing is also much bigger.

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Also when you test fit something you realise what other things are in the way..... like say the transfer box, doh.

So what now hmmmm well the transfer box has to go, at least that gives me a clear space, more on the transfer box later.

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Hi what are you doing with the OLD engine?,

I contemplated putting a 4 pot MAN engine in mine,

fits just right

 

All old bits are to be held on to as if I was ever to return it to a GMC engine I would have all the parts to fit right back on it.

I did consider a 4BT but they sound a bit van like and thought the 6BT would sound more truck like which it does, very nice.

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Hi Richard, at what point did you bury your head in your hands and think 'what have I started on here?':D

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Hi Richard, at what point did you bury your head in your hands and think 'what have I started on here?':D

 

Hmmmm, well it's like this. I do like a challenge, But.

 

Once you have taken the rad and suround off, the cab off, the old engine and gearbox out, transfer box out and other leavers, brackets and thingies ect you are left with a large space from the front of the front crossmember all the way back to the fuel tank, dont forget its a 352 !

 

So when you put something in this space, you then realise with a startling fact that there is no starting point, anything you fit anywhere WILL have an effect on someting else you have NOT fitted yet so where do you start...

 

Go in and think about it for several weeks, well nearly.

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Hi all back again for another installment. In the last pics above you can see the output yoke of the new gearbox is touching the input flange of the transfer box, very bad as there should be a propshaft in there, hmmmm what now, so at this point the engine and gearbox are roughly in the correct place for front to back positioning.

 

Right so the transfer box has to come out for the time being.

 

Below you can see transfer box is about to be removed and lowered down the long piece of timber just above the jack head is bolted to the jack.

 

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Here it is out and on the floor, for your information the split axle transfer boxes are heavy roughly about 100Kg's

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Here is what is left just a very substancial bracket !

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So what to do.... I decided the transfer box had to go backwards down the chassis to give me enough room to get a propin there, so the next step was to decide how to do that. 1- could cut out the original transfer box crossmember and move it backwards, bad idea as it is such a large item and also hot riveted in many places I thought it might prove an issue as it does provide a bracing effect to the two chassis rails.

Option 2- make an identical new crossmember and asociated brackets to fit in behind the original one, good idea.

 

So below you can see the new identical copy of the original one, the second picture shows the top hat profile of the main crossmember I did consider bending this in my teeth as I have done with other brackets ect, but as this is 6mm thick and a tad over 600mm long I got an engineering company to do it, as it turned out the press brake they had was rated at 65 tons and when I went to collect it they said there was not much left in it so quite a job, but it turned out absolutly perfect not a single twist or warp in it, i was well chuffed.

 

 

 

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Edited by R Cubed

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Who did you use for metal fabrication/bending?

 

Just a small private engineering company down here on the south coast.

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Well having got the new super dooper new bent bits of steel for mounting the transfer box I needed to mark out all the holes slots ect then test fit to make sure it all goes where it should. So here you can see the new one fitted just behind the old one.

 

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Just offering up the transfer box to see how it fits, in the first pic you can see the rear of the new gearbox in the background. In the next couple of pics you can see the transfer box temp mounted and the gap between the new gearbox yoke and the transfer box uj flange. Just right for a nice new prop.

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Here you are looking forward from just in front of the first rear axle, just see they both look just right hmmmm.

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Have you mounted the transfer box at the same angle as the gearbox?

 

I was going to comment on the extreme angle of the inter-box prop and then realised I was trying to mate up the gearbox to the output flange for the front axle prop :wow: :rotfl::n00b:

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Have you mounted the transfer box at the same angle as the gearbox?

 

The transfer box has to be mounted square to the chassis rails as that is the way the cross member is fitted, the main gearbox in the pics is not at the correct angle as at this point I had not finished designing and fitting the front engine mount, I think there is a slight angle difference on the uj at the main gearbox end but if I can remember its only about 5deg not ideal but it was the best I could get due to all maner of other things.

 

I was going to comment on the extreme angle of the inter-box prop and then realised I was trying to mate up the gearbox to the output flange for the front axle prop :wow: :rotfl::n00b:

 

Ahhh, after I posted the pics and then looked back at them I did think someone might get the wrong end of the stick but I have to admit the pics are at a bad angle but there you go, and you did twig in the end, or was I doing it to keep you lot on your toes :angel:

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Just for NOS, here you go how about this, it's a bit of a better side view showing the short g box to t fer box prop, below and in the fore ground is the front prop.

 

Inter prop pic (600 x 337).jpg

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Did you manage to keep the props at their original length?

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Nope, sorry to say due to the engine and the gearbox being longer and keeping room between the front of engine and rad for a fan, I had to move the transfer box backwards down the chassis about a foot so the front prop is longer and the rear two props out from the transfer box are shorter the only original prop is between the pilow block and rear rear axle, there is also a custom prop between the ZF gear box and the transfer box too as the yoke on the ZF box is the next size uj up from the GMC ones and it is a custom length to match the gap.

 

 

 

mmmmm nice shiny new props new uj's and ballanced too, what luxury :D

 

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Did you manage to keep the props at their original length?

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Just wondering if you have taken into consideration the increased torque the driveline will be getting. Tooltallmike has done several conversions on Ward LaFrance's with this engine, however, the driveline is heavier duty than the one on a GMC. I do not know if the transfer case and axles would take it as you are introducing a a couple of hundred more pounds of torque into the equation.

 

Your thoughts?

 

John G

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Just wondering if you have taken into consideration the increased torque the driveline will be getting. Tooltallmike has done several conversions on Ward LaFrance's with this engine, however, the driveline is heavier duty than the one on a GMC. I do not know if the transfer case and axles would take it as you are introducing a a couple of hundred more pounds of torque into the equation.

 

Your thoughts?

 

John G

John,

 

The engine spec I fit to WLFs are 125+hp more than this one, however there is still considerably more torque than the original truck design allowed for so I suspect it will have to be driven gently. I wonder what the weakest point of a GMC drivetrain? On a WLF it's the Xfer box.

 

Although it's not remotely the approach I would have taken, as an engineering project it's very interesting and I'm looking forward to the next instalment.:drive:.

 

Regards - MG

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The weakest point was the short intermediate prop between gearbox and T/box, but this is now uprated so I wonder what the next weakest was? On heavily abused trucks it was trunnion bars breaking and diffs (first Timken then Banjo) but that is not likely. Also gearbox input shafts were not that generously sized, so that could be twisted off if someone's foot were to slip off the clutch I guess.

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I agree with Mike on his comment to this being an interesting engineer build. Weak points I am thinking are the axle shafts and the transfer case. As R Cube has fabricated a new mounting point for the transfer case there might be less of a worry at the mounting point as original, however, might have to a keep a close watch on the mounting bolts as the originals were prone to loosening up.

 

John G

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Just wondering if you have taken into consideration the increased torque the driveline will be getting. Tooltallmike has done several conversions on Ward LaFrance's with this engine, however, the driveline is heavier duty than the one on a GMC. I do not know if the transfer case and axles would take it as you are introducing a a couple of hundred more pounds of torque into the equation.

 

Your thoughts?

 

John G

 

hmmmmm you are probably right about the extra torque it's obviously lots more, the conclusion I came to is to drive it cautiously, however regarding the diff / axles due to there being a low range in the transfer box when this is selected the torque multiplication would be increased many times so conclusion diffs / axles could be ok !! we will have to see.

Transfer box is another thing completely I have a plan for this which involves getting new shafts and gears made to do away with the high / low gear selector which I believe is the only real weak point in the split axle boxes, again time will tell.

 

John,

 

The engine spec I fit to WLFs are 125+hp more than this one, however there is still considerably more torque than the original truck design allowed for so I suspect it will have to be driven gently. I wonder what the weakest point of a GMC drivetrain? On a WLF it's the Xfer box.

 

Although it's not remotely the approach I would have taken, as an engineering project it's very interesting and I'm looking forward to the next instalment.:drive:.

 

Regards - MG

 

Mike, regarding the weak points who knows, drive gently yes, there is a definate improvement in acceleration so that in it's self proves there is more torque. There is a guy in the states which runs the bigger 6 pot engine I think 302cu inch which I think produces about 150HP dont know the torque but he also tows lots as well. Going by the rest of the truck all the drive train could be well over engineered and may be fine, we will see.

 

As an engineering project yes I can safely say it has pushed my thought processes to the limit, engineering wise I knew once I started exactly what I wanted to achieve but having never undertaken such a large engine conversion before, the first thing was when you are starting with bare chassis rails everything is variable and where ever you put someting it will affect something else which you have not fitted or some items which have to go back in one place only.

.

Would I do it again....... yes.

 

Knowing now what I do and where parts go it would be a much easier task to make a start. The worst thing I had problems with was trying my very best to make it as respectable as possible first time while not trying to make it someting it's not. Just to look right and not just thrown in and bodged together.

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Ouch....severe pain in the wallet:wow:

 

That was nothing compared to the air brake fittings ect, but thats for later time. :D

 

 

Might just be a touch of tenneritis Degsy.

 

Nope not tenneritis more like fiftyitis :blush:

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Without doubt there have been more than enough GMCs used abused as lime spreaders in the 20 years following the war to establish with some certainty the weak points. I can only go on what I've been told by other people, some no longer with us, but I'm not aware of any ongoing issues with transfer boxes. However there are still a few former operators around who can testify to the CCKW's strengths and weaknesses.

 

One such example is an operator of several trucks who used to replace the banjo axle diffs with units from Chevrolets. He claimed that despite being a bit faster they were actually stronger than the standard CCKW diffs.

 

What do you reckon, Tom? :cool2:

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…. The worst thing I had problems with was trying my very best to make it as respectable as possible first time while not trying to make it someting it's not. Just to look right and not just thrown in and bodged together.

 

Looks like you have done admirably in that respect!

 

Although I think the extent of the alterations you've had to do is almost tantamount to confirming that it is not possible to put a 6B into a CCKW :D:D:D

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