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8T Cat model 12 Grader

17 years 4 months ago #2593 by driggars
Thanks guys for the replys on my Cat 955K, now, I have some questions on my cat 8T model 12.
1st thing, trying to confirm the engine model in it. the engine ser# is 8T2735 and arrangement# 7F3687.
Someone told me it is a D318 engine, but I was talking to a parts supplier on ebay and he claims its a only a 4 cylinder engine, well its a 6 cylinder.
I need to consider either a head gasket kit or go ahead and get an inframe over haul kit. Now the graders ser # is 8T854. so possible someone changed the engine out in early years? since they dont match.

I dont run this machine much, maybe a couple times a year, a few yers back, it was getting comopressiion in the radiator, so I had a guy pull the head, I bought another used head from a used equip. dealer in Ok and they said it had been checked and magnafluxed. After reinstalling the head about 3 months later when I started using it to grade out my road, it started building up compression again in the radiator, bad enough to blow the water out.
It is for sure building compression.

I was told by someone that some of these engines in early years had a different type rod and main bearing ssetup and couldnt get those any longer and I am not sure if this is that model or not?
When I pull the head, of course I know it needs rechecking, but anything else to be looking for that might cause the compression in the radiator?
Who knows, maybe the mechanic didnt torque the head down right? I found this week working oon my 955K head that the head bolds came off using just a ratchet and one hand to break them loose!

Here is the other question, this originally had a pony start which was converted to electric start. Last year I went out to crank it up and the starter turned the engine 1/2 turn and stopped, so I did all the necessary checking of connections and even put on new batteries, still would not worrk,, soI pulled the starter and took it in, they said nothing wrong with it but replaced the bendix since it was just barely catching the flywheel. It still does the same thing, 1/2 turn and it acts like its locking up and will just click. took off agin and brought it back and told them to take it apart and check everything and rebuild everything that is in question, still have the same problem. OH, and did put a new solenoid also. I am wondering if the starter gear is wrong, maybe the rebuilder changed it?

if that is so, where can i get a bendix conversion gear? and anyone know a good place to get the engine kits.
PS: now I am out of breath:)

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17 years 4 months ago #2595 by Old Magnet
Replied by Old Magnet on topic 8T Cat model 12 Grader
Wow, that's a lot of questions:) :)
The 8T model uses the D318 engine (4-1/2 x 5-1/2)
The #2735 engine is 1949
The #854 grader is 1947

Besides head gasket leaks corrosion holes in the pre-combustion chambers and the liners are possible compression leak candidates.

I have not heard of the D318 bearings being a problem or hard to get but the earlier D4600 engine bearings seem to be a problem to source.

What starter do you have?
Original type with inertia drive bendix or later type direct mounted solenoid engagement.

Sorry I don't have source for engine kit, hope someone else does.

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17 years 4 months ago #2596 by SJ
Replied by SJ on topic Grader
Yes that would be a D318 engine and your compression problem sounds like a low liner & compression blows down along the liner where it seats in the block.I have repaired dozens of engines with that problem & possibly the new head gasket just put a band aid on the problem & kept it from blowing down into the cooling system for the short while.The fire eats away at the block where it,s bad & if that is your problem the only thing you can do is remove the liners & check the seats in the block & if the fire has got to it then the only way to repair them is bore the seat out down to good material & install a sleeve to repair it. Cat sells the sleeves & there is two different sizes depending on how bad the seat is burned (eat away).A boring bar is needed to do the job or the special tool that Cat dealers should have so it,s a machinist job unless you are one.Usually a liner should be any where from .002" to .006: above the block projection when it,s drawed down tight in the bore but should be pretty much all be the same height for all the liners.On the head gasket coat the sides with a light coat of #2 Permatex & helps the seepage of the long sides of the head.This was common practice with us at the Cat dealer.The head torque is 130 lbs. for the bigger nuts & 58 lbs. for the smaller ones.Take the torque in two steps & not go the full torque spec. the first time. Spec. says go to 42 lbs. first for the little ones then do the bigger nuts to 90 lbs. first then the 130 lbs & lastly do the smaller ones to the 58 lbs.

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17 years 4 months ago #2597 by SJ
Replied by SJ on topic Inserts
I should have mentioned that if you need sleeves put in the liner ledges then put a little Lock-Tite on the outside surfaces of the sleeves to hold them in good & for a sealing purpose too.

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17 years 4 months ago #2604 by SJ
Replied by SJ on topic Liner Seats
I just remember too that if seats in the block were not too bad they were cut on the bottom of them & Cat had thicker shims to install under the liner to bring it back up to the correct projection.You have to cut the seat till it,s cleaned up & then see if there is a shim that will be right & then the seat will have to be cut a little more for the correct projection in relation to the shim & liner lip thickness.

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17 years 4 months ago #2616 by edb
Replied by edb on topic head retorque
Hi driggars,
new to posting here, OM & SJ are on the money with their advice for your problem. I have recently retired after 43 years with local Cat Dealer. I learnt early on that these old engine head gaskets would lose tension after the first run to operating temperature. So at op. temp. after the first run we always backed the head nuts off about 1 flat ( in opposite order of tensioning) and then would retorque the head nuts and reset the tappets. If possible we used to suggest this be done again after about 20 hours to be sure . As your unit ran about 3 months before pressurising the cooling system this could be a possible cause.
Good luck, regards edb.

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17 years 4 months ago #2617 by driggars
Replied by driggars on topic 8T Cat model 12 Grader

well it didnt run for 3 months and then start acting up, it was about 3 months later that I worked it, right away it was building compression in the radiator. or within a couple of hours

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