D8H Engine Swap

Daniel Davis · Jan 17, 2021

Found a 270HP D8H locally in decent shape with a bad engine. It started knocking, so they tore into it and found a spun main bearing. They shined up the crank as much as possible and stuck a new bearing in it, which promptly spun again. Obviously it needs the crank turned and block line bored (big $$$).

Anyways, I can get it for scrap price. I don't really need another D8H, but I like a good project. I started doing some measuring and found the D342 and torque divider to be 102 inches long from fan to output yoke. I then took a measurement on an 855 Cummins with a 13 speed Road Ranger and it is 100 inches long from fan to output yoke.

Is there any reason I couldn't take the D342 and torque divider out and replace it with a 350 HP Big Cam Cummins and road ranger transmission? Just put the Road Ranger in 9th gear (1.57:1) with the Cummins at 2100 RPM and the output speed would be 1300 RPM - pretty close to the D342 at 1400 RPM with a little slip in the torque divider.

What would it take to make the powershift transmission work? The torque divider pump and torque divider scavenging pump would both go away. Would a single pump mounted on the engine be able to run the transmission and brakes and steering clutches?

Bluox · Jan 17, 2021

Now that's some funny shitt.
Bob

.RC. · Jan 17, 2021

I wonder how a series 60 would go. Would need a bit of counterbalance I suspect.

Tones · Jan 17, 2021

Leave the Jake hooked up in the Cummins

epirbalex · Jan 17, 2021

You would need a governor and an oil pickup for slope work in the crankcase . Some of the Cummings fitted to Komatsu's would be able to handle the pump and governor standard . Are the main blade lift hydraulics to be fitted in front of the motor ? if so can't see why that system can't be used to supply all the requirements . I looked at repowering an old D7 , fella I spoke to it about the options said it would be posible to use a throttle same as a vehicle instead of a governor , would depend on how easy it would be to have the brakes used by your left foot only .

John C. · Jan 17, 2021

That poor old Cummins in that application wouldn't be able to pull a single shank ripper tooth through a cow pasture after a big rain storm. Maybe you could turn the machine into a drag racer and see how fast it could go in the quarter mile.

56wrench · Jan 18, 2021

aw c'mon. we need another engine rebuild thread here. when i replaced the block and crank in my 46a back in the mid eighties, all the block repairs were about $4500 and it looked like a new block, so obviously more than that now. if the crank isn't too bad it may be ground to -.025 or -.050" or maybe the bad journal can be welded and reground. i would talk to a diesel block repair shop and get a couple prices first. it will be easier to rebuild the D342 than cobble together anything else

Daniel Davis · Jan 20, 2021

John C. said:
That poor old Cummins in that application wouldn't be able to pull a single shank ripper tooth through a cow pasture after a big rain storm. Maybe you could turn the machine into a drag racer and see how fast it could go in the quarter mile.

Luckily I do have some cow pasture I need to do some ripping in.

That was actually my first thought as well that an 855 will only have about 2/3 the torque at a given horsepower rating compared to the D342. But horsepower is simply a measure of work - if the speed of the Cummins is reduced via a transmission, the torque is increase. 350 HP at 2100 RPM is still 350 HP when reduced to 1400 RPM in the transmission, but the torque is increased to exactly what a 350 HP D342 would produce at 1400 RPM.

As for the quarter mile, it should be able to clock a little less than 50 seconds at 2300 RPM - in reverse.

Daniel Davis · Jan 20, 2021

56wrench said:
aw c'mon. we need another engine rebuild thread here. when i replaced the block and crank in my 46a back in the mid eighties, all the block repairs were about $4500 and it looked like a new block, so obviously more than that now. if the crank isn't too bad it may be ground to -.025 or -.050" or maybe the bad journal can be welded and reground. i would talk to a diesel block repair shop and get a couple prices first. it will be easier to rebuild the D342 than cobble together anything else

Only one machine shop around that could handle the D342, and they are not cheap, but they are the best. Anyways, starting at $5K to have the block welded and line bored, another $2k to have it milled and counter bores cut. More if they run into problems. They will not weld the crank as they say it takes the hardness out, but grinding should clean it up - have another shop that can do that for a more reasonable $400.

Anyways, I am looking at $7500+ to get the block and crank fixed. I haven't even called Cat to get a price on a complete rebuild kit and pair of reman heads, but I am going to guess at least $15K. Add a few little parts and I am figuring on $25K to $30K to get it done the right way. If I had a need for another D8, that would be a good option, but I don't really need two...

Or, I can take a cheap Big Cam and 13 speed and a can of welding rod and have it running for much less than $10k.

My biggest concern is how to make the transmission oiling system work without the torque divider. I can easily handle the rest.

John C. · Jan 20, 2021

I think your numbers for the rebuild are pretty close from my experience.

I'm wondering how you are going to fit the engine and transmission over the equalizer bar frame and then hook up to the D8 transmission.

You are also forgetting about the torque multiplication of the torque divider and the fact that the old Cat can deliver peak torque all the way down into the range of 750 to 900 RPM. Don't get me wrong though. I think it would be a great project just for the knowledge at the least.

d9gdon · Jan 20, 2021

You'd be better off buying that tractor for scrap price and using it for a parts machine to support another decent one that you find cheap at an auction or somewhere else. You don't yet know if everything else is right on that one. It could have a bad converter or final drive that would show up if you were able to work it before you bought it. You could wind up fixing the engine only to find out it's got another failure.

If you contaminate it with that Cummins, you won't have a Cat anymore...you'll have a Frankenstein tractor that won't perform right or that you can't resell when you're done with it. Cat made a whole pile of the D8Hs and I've been down this road with cheap equipment just needing an engine or final drive or transmission...and damn if it don't always cost way more in the end than just being patient and finding a well cared for tractor.

Just my thoughts...

Daniel Davis · Jan 21, 2021

John C. said:
I think your numbers for the rebuild are pretty close from my experience.

I'm wondering how you are going to fit the engine and transmission over the equalizer bar frame and then hook up to the D8 transmission.

You are also forgetting about the torque multiplication of the torque divider and the fact that the old Cat can deliver peak torque all the way down into the range of 750 to 900 RPM. Don't get me wrong though. I think it would be a great project just for the knowledge at the least.

Yes and no. I was figuring the D342 was good down to 900ish RPM as well, which through the truck transmission would be 1350 RPM for the engine. 350 Cummins peak torque is 1300 RPM so it still looks to be a good match.

I am not sure how to figure in the torque divider, so I figured it would be like a D8H 36A instead of a 46A. If more torque is needed, the truck transmission can be shifted down to greatly increase torque - it just won't be "self adjusting" like the torque divider.

As for making it fit, twin counter shaft transmissions are not very tall. My tape measure says it will all fit with ample room on all sides. Just a short driveline will couple the transmissions together.

Daniel Davis · Jan 21, 2021

d9gdon said:
You'd be better off buying that tractor for scrap price and using it for a parts machine to support another decent one that you find cheap at an auction or somewhere else. You don't yet know if everything else is right on that one. It could have a bad converter or final drive that would show up if you were able to work it before you bought it. You could wind up fixing the engine only to find out it's got another failure.

If you contaminate it with that Cummins, you won't have a Cat anymore...you'll have a Frankenstein tractor that won't perform right or that you can't resell when you're done with it. Cat made a whole pile of the D8Hs and I've been down this road with cheap equipment just needing an engine or final drive or transmission...and damn if it don't always cost way more in the end than just being patient and finding a well cared for tractor.

Just my thoughts...

All good points. I don't really know the guy who owns it, but I am good friends with the local mechanic that has worked on it several times over the last 10 years. He says it is a solid machine outside of the engine. Obviously a final drive could give up the ghost in another 10 hours, but that risk will be there with any used equipment.

I can buy it for a little under $150/ton. At that price, I can't get hurt. If I swap in a basically free engine and tranny, I can get it going for less than another $5K. If it works, great. If not, I can scrap the Cat, sell the engine and transmission, and only lose out on my time. I have a good track record for making Frankenstein builds work well, so I think it's worth the risk.

Back to my main question:

Will the transmission work standing alone without the torque divider with just one pump driven off the engine?

alaskaforby4 · Jan 22, 2021

This sounds like a fun project, looking forward to reading it happen! Good luck!!

em7-300 · Jan 23, 2021

Daniel Davis said:
Found a 270HP D8H locally in decent shape with a bad engine. It started knocking, so they tore into it and found a spun main bearing. They shined up the crank as much as possible and stuck a new bearing in it, which promptly spun again. Obviously it needs the crank turned and block line bored (big $$$).

Anyways, I can get it for scrap price. I don't really need another D8H, but I like a good project. I started doing some measuring and found the D342 and torque divider to be 102 inches long from fan to output yoke. I then took a measurement on an 855 Cummins with a 13 speed Road Ranger and it is 100 inches long from fan to output yoke.

Is there any reason I couldn't take the D342 and torque divider out and replace it with a 350 HP Big Cam Cummins and road ranger transmission? Just put the Road Ranger in 9th gear (1.57:1) with the Cummins at 2100 RPM and the output speed would be 1300 RPM - pretty close to the D342 at 1400 RPM with a little slip in the torque divider.

What would it take to make the powershift transmission work? The torque divider pump and torque divider scavenging pump would both go away. Would a single pump mounted on the engine be able to run the transmission and brakes and steering clutches?

It's funny, I was thinking about doing the same thing on a D4D. The engine is proving difficult to find. Not being familiar with the Old Cat stuff, I am wondering about tying into the shaft behind the flywheel housing with a different engine. One question is how fast the shaft needs to spin. There appear to be a lot of old Cats with bad engines. I can weld the block on the one I have but a commonly available replacement engine would be good if the swap is possible. I take it the torque divider attaches to the flywheel and multiplies engine torque?

Puffie40 · Jan 23, 2021

em7-300 said:
It's funny, I was thinking about doing the same thing on a D4D. The engine is proving difficult to find.

The D4D used a 3304 engine, which was also used in the 930 loaders amongst other applications. There are even turbocharged versions available. You could also consider the 3304B engines as well.

Speaking of turbocharged, any engine swap you do will have to keep the original power output in mind. I remember reading on the ACMOC forum years ago about a cummins repower of a D8 land clearing machine, and while the cummins almost doubled the power output, the D8 started tearing up transmissions.

em7-300 · Jan 23, 2021

Puffie40 said:
The D4D used a 3304 engine, which was also used in the 930 loaders amongst other applications. There are even turbocharged versions available. You could also consider the 3304B engines as well.

Speaking of turbocharged, any engine swap you do will have to keep the original power output in mind. I remember reading on the ACMOC forum years ago about a cummins repower of a D8 land clearing machine, and while the cummins almost doubled the power output, the D8 started tearing up transmissions.

That's interesting. Are the 330 and 3304 all basically interchangeable? Same basic block, flywheel housing? I understand Cat changed some things but if it will bolt in, that would help.

.RC. · Jan 23, 2021

I am wondering how long the transmission would last with no torque converter. Or the drive shaft for that matter.

Although I did hear a story once of people removing the torque converter from D9G's or H's to be used for blade ploughing. It might have been a narnia story as I have also heard stories of fitting lock up torque converters to D10's for blade ploughing.

Puffie40 · Jan 23, 2021

em7-300 said:
That's interesting. Are the 330 and 3304 all basically interchangeable? Same basic block, flywheel housing? I understand Cat changed some things but if it will bolt in, that would help.

As far as I know, they should be almost the same dimension-wise.

This HEF thread might help you out. It sounds like the engine parts won't interchange, but you should be able to swap out the entire engine in the tractor with very few changes.

Old Magnet · Jan 23, 2021

What s/n is the D4D? If it's early with the D330A (4-1/2" bore) it does not readily interchange with the 3304. If it now has the D330C engine (4-3/4" bore) upgrade to the 3304 has been done without to much hassle.

D8H Engine Swap

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