D339 Decompression linkage

Under normal run mode the clearance between the compression release push rod and the rocker arm is 0.025 to 0.030". The push rod is free floating and is controlled by the compression release camshaft.

The parts book lists these parts on the decompression pushrod
2A1278 "end" which bears on rocker arm and screws onto top of pushrod
1B4203 "nut" (locknut)
6B4040 "rod" Bottom of rod appears to bear directly on decompression cam shaft which is in engine block

I think I would lift the rocker arm assembly and remove the decompression pushrods to investigate..........however, as I'm sure you know, there are a lot more likely causes for a rattle or knock than a decompression pushrod. (I can't see how that would make any noise at all)

One you might not have thought about is a bad injector or an injection pump that needs the lifter set as these would affect ignition timing and can result in anything from a rattle to a bad knock. Then there are the more worrying problems with connecting rod bearings, foreign matter on top of pistons (dropped valves etc).

What is your interest in this machine? Potential purchase? fixing it for someone?. If you're purchasing it, you may want to consider a lot of other things about the tractor rather than keying in on the engine and the rattle.

I am considering purchase as it is being sold for about scrap price. I am here because I do know enough to know there are MANY things that I might not know about these old CAT motors. Given what you folks have shared, I am leaning towards a stuck valve holding the rocker away from the decomp push rod (though the rocker push rod is tight, don't know if lifter in on ramp of cam or base though and I will have to go back to trouble shoot). Not sure what to make of the lifter injection timing but I was told it ran fine the developed a rattle (I can not confirm that) vs right off the bat which I would imagine a timing problem would be. I did manage to stop by the local Cat guru (50+years of owning operating and servicing his stuff) and he mentioned that the lifters has some sort of retainer that has a fastener (bolt/stud) that may have not been properly tightened and came loose. He also said that if that was the case, it didn't matter how much the was invested overhaul.... it was an indication of poor workmanship that could not be trusted. Around here older D7E cats seem to sell for $12000 to $20000 depending. The one I am looking at has 90% UC and that's what got me going on the notion of "simple" engine work to take a chance on it.

I guess I am duly scared at this point and the "getting a deal" for the price of scrap it looking more like a money pit. Probably should just scrape together another $10k and get a working 7E that has a record of maintenance and ready to go to work.

Thanks again....

BTW - I have a line on an older 17A as well but local Cat guru seems to think that the operation of the manual steering is not for the faint of heart. I will search the blog here on that abandon that notion of a 17A. I am used to my old Cletrac BG6 with 10' road blade so how bad can a CAT be compared to that?

Seems you are giving up rather easy....without troubleshooting.
Developed a rattle doesn't give much to go by. Are you talking single cylinder or whole engine? What kind of rattle?....valve clatter, injection, rod???????

If you are unfamiliar, try and find an old Cat guy that can help diagnose.

If the undercarriage is 90%, then even if the engine is totally shot, you could buy another for scrap with a good engine, and transplant it if you can get it for less than the extra 10k it would take to get a good condition unit with good u/c. Value is mostly on undercarriage as you know.

I hear ya, but the real problem was with the lack of consistent pressure to make the machine move. The rattle developed while the "new owner" was removing the blade and moving the machine (20-30 feet a pop) about one hundred yards to the location he was going to work on the problem when it "reportedly developed the rattle". I do have an old Cat guy (as of today) but between the rattle and original converter issue (shaft stops moving) it is too much for this newbie. It is well worth the money but I do not have the luxury of time as I need the machine for work by summer. It can be had for $6k to someone who wants to get it going. It could be just a couple of thousand or it could be another $10k to get her up. Still worth it but for the time. Too many of the things I have been told don't jive for my liking.

I rather go for a fully operational one for more money... I do have the contact info if someone in upstate NY is interested in this one. It's got too much going for it to scrap.

Thanks for all the help and insight... I am going to own a Cat within the next 30 days! It will be a D7 too.

[attachment=23403]D7 RES.jpg[/attachment] Old Magnet, I am only going by description as I did not want to start it until I had a better understanding of the engine. What I know now (with much thanks to you folks here) is that it can not be anything to do with the decomp assembly but maybe a stuck valve, lifter issue or injector/timing. Once that is solved then a pressure test can be done to help trouble shoot the converter issue. It all may be simple (nothing every really works that way) and readily fixed. I myself have a bad back and can not "steadily" work or lift heavy parts any longer so am slow and must pay for help. Hate to admit it but that's my reality. It seems like it is priced right so someone can get it going but I am looking to use it in short order.

Thanks again, this is a great place for Cat knowledge.

I would look seriously at that 17 A. They were always my favorite.