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What gave the 13A d8 more power?

17 years 1 week ago #3214 by OzDozer

Thanks, Oz and Kelly for the run down on the D8 13000. Some points to be aware of when swapping engine parts!

Yes - it's crucial that you acquire parts books for any engines you want to swap parts between .. so you can compare parts and design changes. Some engineering changes are very subtle, and can cause you grief, if improperly mixed.
A classic typical situation, is that nearly all turbocharged engines use oil-cooled pistons .. but N/A engines do not. So if you commence an engine swap, with an N/A basic engine, and just add a turbo, you can end up with melted pistons.

So to recap, increases in HP before the 13A were accomplished by upping the RPM, using a stronger spring or lighter weights, different injector pump cam and letting the rack open up more.
With the 13A a change to valve timing and beefier pistons on top of these tweaks?
Accompanying the increases were the change to precision bearings, improvements in crankshaft and piston design and metallurgy, oil delivery/cooling as well as the screw-in injector heads. There were defenitely some key turning point changes!

Yes, there were some substantial engineering upgrades to the 13A engines, based on rapidly improving technology, related to steels, and alloys, in the early 1950's.
The D9 was being built from scratch, in this era .. and the D9 required new steels, and advances in technology, because the massive weight and HP for the time, was putting Cat into totally new territory, in relation to the then-currently available steels and alloys.
Some of that D9 research, no doubt, went into 13A engine design.

OM - I think you'll find that Cat were very conservative on the installation of the early turbos, due to the fact that they were concerned about reliability becoming a problem, if they went overboard on HP increases with turbos.

The turbos were initially touted as a godsend for high altitude work, as the turbo engines don't become affected as badly at altitude, as the N/A engines. I gather, that the engineer thinking in the early 1950's, was .. that major HP increases, were not seen as a primary reason for turbos .. but rather, improved performance at altitude.

Once the turbos had been tried and proven in the field, and more advanced research work done on potential engine problems, Cat then commenced to boost HP with the turbo engines.

It was found, of course, that better quality valves and oil-cooled pistons were needed to counter the increased combustion temperatures on turbo engines .. but that decent HP increases could then be obtained, without sacrificing reliability.

It was understood that turbos could lead to substantial power increases, by larger and longer combustion times .. but it took testing to see if the increased power would lead to major failures.
As we all know well, nowadays .. turbos provide a smooth increase in power via increased combustion pressure down the full length of the power stroke .. but in the early days of turbos, there were many of these factors that needed to be tested and studied, before they were translated into improved design .. otherwise reliability would suffer .. as would Cat's jealously guarded reputation, along with it.

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17 years 1 week ago #3215 by Kelly
Replied by Kelly on topic D8 Pusher and D813A.

Kelly - I'm a little short on Service Magazines, Service Reporters and general new model releases in the 1953-1954 period.
Was the 13A available in a "Standard D8" form, as well as the "Pusher D8"? If so, what were the differences?

Yes they were, as I understand it, the pusher was build from 13A1 through 13A234 and equipped with the 3H1906 Transmission Group. The newer standard D8 Tractors retained the same 13A series of serial numbers as the former D8 Pusher Tractor. For pusher applications a pusher arrangement 3H5676 was offered. This was the new standard D8 Tractor equipped with heavy duty track roller guards, and the 2000 pound counterweight, a 3H1906 Transmission Group and crankcase guard. The later D8 Tractors came with the larger fuel Tank more commonly know as the “Bubble Tank” which became effective with machine SN 13A959. (Caterpillar Service Magazine, June 11, 1954)

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17 years 1 week ago #3231 by maximan
Here's a question. In the earlier 2U's there is a transmission case reinforcement shown in the parts book - basically a rod threaded on both ends. It looks like it would run front to back on each side of the transmission case. Was this due to the increased horsepower, or was it to allow the attachment of tools to the back of the case without ripping it off?

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17 years 1 week ago #3233 by SJ
Replied by SJ on topic Turbos
Turbos were good up to 7500 ft. elevation listed for truck engines but I know some turbos on tractor & truck engines had a finned ring to direct flow so they wouldn,t over speed & they were engineered at a certain angle to do it. There were other rings if engines were used in real high elevations to direct the flow at a different angle to keep the RPMs up on the turbo so it would put out the required boost for listed HP.

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17 years 1 week ago #3236 by Kelly
In a since your right….. although there were not put forth as such. The cast iron transmission cases of earlier D8 Tractors which engaged in severe operations ….(no mention of the increased horse power of the tractor.) could be strengthened by installing the reinforcing group bars. There was more than one group of the reinforcing bars because of the earlier transmission case design, some of the earlier cases had no provision for the fastening of the tie bars. The 5H414 Reinforcement Bar Group was adaptable to these cases.
These reinforcements groups were adaptable to all early transmission cases which did not contain threaded bosses at the rear of the case or machined bosses at the front. Adaptability of these groups were applied to all 5E, 1H, 8R, 2U, and 13A Series D8 Tractors up and through serial number 13A738. 4H6194 Reinforcement Bar Group included shorter tie bars and was directly adaptable to D8 Tractors 13A739 through 13A1001, there is other Groups as well.

Effective with D8Tractor serial number 13A1002 this reinforcing became standard equipment on cast transmission cases.

The author help the local Caterpillar Mechanic install a set of these reinforcing bars in a very early D8 13A after losing the bevel gear and pinion then finding the case was busted under the bevel gear bearing cage.
The whole tractor was dismantled and the case was taken to the local black smith for repair.

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17 years 1 week ago #3239 by jbdoug
Maximan, interesting on the reinforce kit for the D8 .Was not aware that it was that big a problem.Dad pulled a D8 apart to replace the main case and while i was still in school in 52 helped out on repair. Was an 8R and always thought with the frame that they were quite strong. most had the cable blade with Isacson front unit and lift frame. The logging cats usually had winch on back and look like that would apply quite a leverage across the case. On our 1H model probably stressed the heck out of the case while land clearing lots of heavy stumps. With a winch on it the D8 was pretty well balanced but still could stand her on her toes while lifting stump out. What was considered severe service in Cats view or did they give any examples? Have to keep an eye out and see if many of the kits were put on. Always learning something new>> John D

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17 years 1 week ago #3243 by MTMike
Very well said Thanks for all the good info and Thanks for taking the time to Post the info MTMike

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17 years 1 week ago #3244 by Kelly
I don’t think you’ll find the above mentioned reinforcements groups rods available in the earlier years of the D8’s. Not until the mid-part of 1954 were they available, yes after that date, they were available for the early tractors as well.
Your repair job in 1952 would have been a little early for the reinforcement rods to be added to the transmission.

Not until serial number 13A480 was the bevel gear case (transmission case) reinforced at the factory which help prevent case brakeage.

The case strength was increased by: 1) Increasing the thickness of the bevel gear cover (“doghouse”) seat. 2) Increasing the thickness of the bevel gear bearing supports (“saddle”). 3) Increasing the thickness of the vertical walls under the bearing supports and seats. 4) Increasing the thickness of the vertical wall ribs. 5) Reducing the diameter of the oil drain-back hole in the bearing support to 5/8”.

It is interesting to note that when installing the bars the front retaining nuts were torque between 100 and 150 pound feet, in excess of 150 pound feet may disturb the bevel gear adjustment. Torques below 100 pound feet did not give effective support.

On can only guess what the stress would have be on back of old D8 with a Hyster 3 Drummer (Yarder).


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