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Discussion Starter #1 (Edited)
I am in the process of building sort of a FrankenCAT. I'm using a 4MG B model block and pump with a wide journal crank and rods. I have some questions about piston and nozzle selection. I was planning to follow Ynot's 625 C model formula. I am a little confused, however, since in the parts list it says that the pistons should be 14.5 compression ratio but when I talked to CAT the parts guy broke down the OR3783 cylinder packs and gave me the piston number of 7E-8656 which is a 15.6 CR. Maybe I missed something and transposed a number when talking to him or misunderstood the original parts list posted by Ynot. If anyone can clarify I would appteciate it. As far as nozzles go, will the OR8785s work with my pump? I did some reading that suggested that those nozzles pop at a higher pressure than the B pump operates at. If not are there nozzles that will work well with both my pump and those pistons or do I need to modify the pump?

Thanks in advance for any help you can provide.
 

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Discussion Starter #2
Are all the CAT gurus gone?
 

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I am in the process of building sort of a FrankenCAT. I'm using a 4MG B model block and pump with a wide journal crank and rods. I have some questions about piston and nozzle selection. I was planning to follow Ynot's 625 C model formula. I am a little confused, however, since in the parts list it says that the pistons should be 14.5 compression ratio but when I talked to CAT the parts guy broke down the OR3783 cylinder packs and gave me the piston number of 7E-8656 which is a 15.6 CR. Maybe I missed something and transposed a number when talking to him or misunderstood the original parts list posted by Ynot. If anyone can clarify I would appteciate it. As far as nozzles go, will the OR8785s work with my pump? I did some reading that suggested that those nozzles pop at a higher pressure than the B pump operates at. If not are there nozzles that will work well with both my pump and those pistons or do I need to modify the pump?

Thanks in advance for any help you can provide.
The cylinder pack you need is a 10R1439, this is a 14.6:1 two piece steel crown piston. The matching nozzle for this is an 0R8789 which pops close to 3500psi and would cause excessive wear in your B pump.

The only way to get that pressure is to swap to a C model pump, but in an ideal situation it would be a full pump build to get the right timing spec on the pump cam to match the lower compression.

If you buy 0R8789s you can send them to Diesel Controls in ohio and have the pop pressure lowered to better match your B model pump, or you can go with 0R3421s and hope you hit your pump timing spot on to not have them trailing smoke.
 

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Discussion Starter #4
Thank you for the reply. Of course in my simple mind it brings up more questions. Apparently the Ynot parts list is not appropriate for my application. I like the idea of funning steel crown pistons, but I've been told by a couple different CAT mechanics that the only way to run them in a C is to build ut to 8PN specs with OR9424 cyl packs, OR8290 nozzles, and an OR 4886 head and that running a standard head with two piece pistons can lead to valve clearance issues.
Do you happen to have the piston numbers for the ones in the 10R1439 packs?
Also, the nozzles I have now are OR3432. Are they good for anything other than paperweights?
Sorry for all the questions but I've been getting a little overwhelmed by all the information I've been getting from interwebs reading and live conversations as well.
 

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Just gonna throw this in- Do yourself a favor, unless you are gonna send your nozzles off to someone competent to thoroughly test examine and adjust them, BUY NEW -NOT REMAN Nozzles. They will start with a prefix other than OR. Example, iirc, 7W-7031 is same as OR-8785. Even at that I would imagine the pros like Cody is recommending would much rather deal with new. I , as well as some others, have had really poor luck with Reman sticks.
 

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I will say this now, you can either take the info I give you and use it or just forget I posted it.

Why are you under the impression that a steel top piston can't be used unless it came from an 8pn?

The 3406C generators that run them are not that different from truck engines, these engines are where you find the highest output as well as the pump cams that aren't designed for emissions.
 

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Discussion Starter #7
I will say this now, you can either take the info I give you and use it or just forget I posted it.

Why are you under the impression that a steel top piston can't be used unless it came from an 8pn? .
I'm sorry, I'm not trying to insult you. I had no idea what type of application those were from. I'm just going off what I've been told by a couple of mechanics (who deal mostly with truck engines) and also from reading on this site where some folks said they tried steel tops and didn't like them. That said, I just reread some of your old posts and noticed that you mentioned the 8789 nozzles and that they have a matching steel top three years ago. I just didn't see a piston number with it.
Again, I'm just a little overwhelmed by all the different formulas and part numbers I've come across. I appreciate your help.
 

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125-8869 is the crown # for the 14.6:1 steel crown...takes the same skirt as 8pn steel top but some of the rings are different. Theyre the only way to go for building reliability and the most power.
 

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Discussion Starter #9
125-8869 is the crown # for the 14.6:1 steel crown...takes the same skirt as 8pn steel top but some of the rings are different. Theyre the only way to go for building reliability and the most power.
Thank you much.
Any idea if 100-3851 double oilers are appropriate for the application. They are what was in the engine that is donating the crankshaft and use 3/8 bolts so I wouldn't need to drill and tap the block if they're ok to use.
 

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166-3650 is the double piston cooler nozzle you need that uses the 3/8"s bolt. Also need the higher pressure oil pump releif valve spring retainer as well.
 

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Discussion Starter #11
166-3650 is the double piston cooler nozzle you need that uses the 3/8"s bolt. Also need the higher pressure oil pump releif valve spring retainer as well.
Thanks for the number. I do happen to have a pump that is already set up that way so I'm good there.
 

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The 0r8290s i found in sis on an 8pn serial, anyone know what they flow compared to the 8785s.

Believe what they say about reman nozzles, ive put a second set in after being told there was no new inventory and a year later I'm suspecting they're junk, again.

For a 3zj, would the steel 14.5:1 or 16.1:1 be a better option?
 

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7W-7031's have been on national backorder for 6mos -or at least that I know of. Last time I asked I was told there were like 19,000 on backorder. That sounds a bit fishy to me. That is the new number for an 8785. You may already know this but the 8785's were never specd with a steel top. Came with aluminum pistons, marine spec [email protected] A good serial number for that spec is 4tb04640. Not sure , but I think 8290's flow a tad more. I do know that pop on 7031's is around 2300psi and 8785's are considered in spec down to 1600psi. Which in my opinion is allowing way too much tolerance in spec. I want to see them all within 200psi- 300 at max. But that is just me. The 7031's I have popped have been around 2300 new out of box and the 8785's out of box at about 1800 + or - 200psi.
 
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