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Crawlers, Dozers, Loaders & Backhoes Discussion Forum

jd 450 rod cap screws

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dickpoinsett

08-02-2007 07:10:32




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Putting new rod and main bearings in my JD 455 crawler loader. Shop manual warns against reusing the rod cap screws. Can someone explain the reasoning behind this warning and/or the consequences of ignoring it. Thanks.




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jdemaris

08-02-2007 10:42:28




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 Re: jd 450 rod cap screws in reply to dickpoinsett, 08-02-2007 07:10:32  
The concern is plain old metal fatique. Deere didn't use to give those warnings to the same extreme when the rod bolts were tightened via a torque-wrench. Deere used to give length specs of a bolt. If it measured okay, it was reused - no problem. I suspect those bolts were better quality. When they changed over to "torque-to-yield" settings with newer style bolts, bolt replacment was suggested at every teardown. Any type bolt is simply a spring. You tighten it and it stretches - and hopefully retains it's tension. If it does not, it gets loose. If you tighten it more to compensate, it will get longer and eventually break. I probably rebuilt hundreds of little Deere three and four cylinder engines like your's - and with most of the older ones - the rod bolts got torqued to 52 lb. ft. and reused, over and over. I don't recall ever seeing one fail. Funny thing is, I saw several fail with the later configuration. I've also had several other makes lose engine due to failed bolts, including several Case tractors with 188D engines. New bolts are usually a cheap investment - but I have to watch what I call "cheap." I just bought new rod bolts for my 200 c.i. four-cylinder Allis Chalmers and it cost me over a $100 - AND - requires some new machining on the rod caps to use them. By the way, if you are doing a rebuild - you ought to get the big ends of your rods checked and/or resized. That IS an important issue. They tend to get slightly egg shaped as engine hours add up - and you need to get them closed up and made round again when putting in new bearings.

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dickpoinsett

08-05-2007 07:01:40




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 Re: jd 450 rod cap screws in reply to jdemaris, 08-02-2007 10:42:28  
Thanks for the reply. I intend to install new cap screws. The machine I'm working on is a 1986 455E and my shop manual doesn't mention torque to yield bolts. In fact the spec page at the beginning of section 0403 specs the cap screws at 52 lb-ft while the text on pages 0403-03 and 0403-10 specifies 95 lb-ft. I thought it was a typo on the spec page until you specifically mentioned the 52 lb-ft number in your reply. Do you have any thoughts on which is the correct number? Thanks

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jdemaris

08-05-2007 07:58:26




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 Re: jd 450 rod cap screws in reply to dickpoinsett, 08-05-2007 07:01:40  
95 foot pounds cannot be correct if it's the standard Grade 9 or 10, 3/8" or 7/16" bolt, fine-thread bolt. (I cannot remember). 52 lbs. was the original spec., and in some applications it got jacked up to 65 pounds - and that's the high limit - until "torque to yield" began to be used. If you buy new rod bolts from Deere, I suspect they will come with new "torque to yield" specs - but, who knows?

Personally, I prefer the older torque specs. But, the industry has shyed away from them because those specs. depend on variables - such as the threads being properly lubricated when torquing - and lately everything is being "dumbed down." Someone decided that, by using "torque to yield" specs, the job of tightening would be less dependent on lubricating bolt threads properly.

Funny thing is - I just got new and updated bolts for my Allis Chalmers diesel - and - now, they've dropped the "torque-to-yield" specs. They gave me a long list of different standard torque-wrench specs depending on what specific type of lubricant I use on the bolt threads.

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Bob

08-02-2007 07:41:28




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 Re: jd 450 rod cap screws in reply to dickpoinsett, 08-02-2007 07:10:32  
Rod bolts stretch a little each time they are tightened, plus they get the snot beat out of them in use.

Sooner or later, they MAY fail.

What do YOU suppose the consequences of that are???

Which would YOU rather buy, a few dollars worth of bolts, or a replacment engine, should the block get "ventillated" by an errant connecting rod?



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