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Author Topic: JP2 big end bolts  (Read 852 times)

Seedyh

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JP2 big end bolts
« on: March 08, 2022, 05:35:21 PM »
I'm rebuilding an early (32/33) JP2 and hope someone can advise on big end bolt tightness.  Having tightened according to the book and loosened the two bolts by one half turn they are now loose!  This surely cannot be right?  All other engines I have worked on all bolts are torqued equally.

Another query - the piston scraper ring is narrow and unslotted but tapered on one side. Is it taper up or down?
Many thanks

cobbadog

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Re: JP2 big end bolts
« Reply #1 on: March 09, 2022, 05:21:48 AM »
Hi Seedyh,
The torque setting should not be loosened once set and is why you have slack. What did you read that advised that to be done so it can be corrected. Whenever I need torque settings and don't have a manual I simply Google the bolt size and thread pitch in torque settings and that will always be right on the money as torques settings are mostly done by the bolt size.
I have never heard of torquing a bolt then loosen it, very strange indeed.
As for the taper on the oil ring. This is something best left to someone with a manual but at a guess I would face it down so it scrapes the bore and the oil back to the sump. BUT wait until someone who does know the answer to this please.
What will you be doing with the engine once you have it running? Always good to see some pictures of projects as well but they must be compressed to load up onto the Forum.
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Diesel Engineering

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Re: JP2 big end bolts
« Reply #2 on: March 10, 2022, 07:57:26 AM »
According to the parts book the piston is fitted with 4 rings. The top ring is tapered, the next  2 are normal rings and the 4th is a slotted scraper ring.
The big ends are not a straight forward fit like the more modern engines especially if new bearings are being fitted. It is important to check the clearances as they may need scraping to get to the correct clearance.

cobbadog

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Re: JP2 big end bolts
« Reply #3 on: March 10, 2022, 10:29:00 AM »
Now the tapered ring makes sense going on the top groove to avoid hitting any lip that may be there.
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mobile_bob

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Re: JP2 big end bolts
« Reply #4 on: March 10, 2022, 02:04:02 PM »
this tapered ring question is interesting, at least to me...

my experience tells me that i would want the larger diameter (taper up) for the top ring
the reason being is that i would not want the pressure from compression and firing to be able to get between the taper and the bore, otherwise it would want to lift the ring off the bore.

all i have ever seen with other engines places the taper so that it scrapes up toward the cylinder head.

however having said all this, i would be interested to see a reference to what this manufacture has to say on the subject, and maybe their thinking as well?

i am with cobbadog when it comes to torquing, i can't remember any reference relating to torque where one is directed to torque to a set point then back off.  however there is a "torque turn" method somewhat widely used, where you torque to a specific rate, and then advance (tighten further) by some specified amount, such as 120 degrees or some other amount.

i also agree that short of having a specified torque for a bolt from a manual, i would do as cobbadog states, google the size of the bolt (also grade and thread pitch) and get a torque rating and go with that. that generally will get you well within the tolerance given by the manufacture.

fwiw
bob g

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Seedyh

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Re: JP2 big end bolts
« Reply #5 on: March 10, 2022, 04:47:54 PM »
Many thanks for your replies.  The con rod bolt instruction is in the Lister JP/JK/JS manual admittedly a much later book than the engine which is from an early Ruston loco.  The heads have an annular ring machined to fit over the liner rims and uses copper rings/shims to set bumping clearance.  One piston is a replacement and has the normal ring set up the other one is probably original with the tapered scraper ring.  The liners are chromed and in very good condition with no perceptible ridge at the top.
The big end shells are being reused as in good condition.

cobbadog

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Re: JP2 big end bolts
« Reply #6 on: March 11, 2022, 03:31:48 AM »
Hi Bob, the ring sets provided for tractor engines when rebuilding offer the tapered ring to be fitted to the top position and in way that the narrow or thinnest side of the ring faces up to avoid any lip on the bore. Some kits that are supplied with the new liners do not have this taper ring at all. I purchased a made to measure set of 6 rings to fit an old McDonald Crude Oil Engine from 1945. I was not boring it out and only honing it. The ring set when made and after asking me if the engine is being bore or had been. I replied no just a hone then they made a tapered ring for the top and had it clearly marked with a description that said this side up.
I have heard of it for car engines too.
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Diesel Engineering

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Re: JP2 big end bolts
« Reply #7 on: March 12, 2022, 07:15:10 AM »
 A couple of attachments showing piston rings and big end fitting. Maybe of some help.

mobile_bob

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Re: JP2 big end bolts
« Reply #8 on: March 13, 2022, 04:25:30 PM »
cobbadog

thanks for the info

goes to show and old dog can learn a new trick or three!

everything i was ever taught was to remove the lip/groove at the top of the cylinder, then hone, and then put in the rings with the taper down.  but then again, i was taught nearly 50 years ago, and mainly on mid and heavy diesel engines.

one higher compression engines, i wonder how they keep the ring flutter down?  one would think that the higher compressions and higher pressures from ignition would lift the rings?  but maybe that is not the case on lower compression engines?  maybe even on higher compression engines, if the rings are made stiffer or have added expanders?

interesting indeed,  i could see how a stepped ring would be advantageous if you had a ridge/lip/groove at the top of a cylinder,  having a step would keep the ring from contacting that and being damaged.

i suspect there is a compromise being made, in order to not have to remove the ridge/lip/groove and being able to just give the bore a quick scuffing to remove the glaze and put the engine back together again and get it back in service without having to tear down for rebore or resleeving the engine. i suspect the lifespan is shorter than going with a complete overhaul. 

but what do i know?
i have been wrong before, just ask my wife!  :)

bob g
otherpower.com, microcogen.info, practicalmachinist.com
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cobbadog

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Re: JP2 big end bolts
« Reply #9 on: March 14, 2022, 04:46:53 AM »
Bob, no doubt you would have forgotten more than I would ever know. But over the last 12 or so years with doing engine rebuilds on old vintage tractors, stationary engines and mowers I too have been advised of some new tricks put into action by those who have followed us through on the journey of engines and their ways of bringing us unstuck.
The old McDonald had a lot of issues from lip to an unusual ring size both in diameter and thickness. These were made to measure over in Ne Zealand. These guys also advised about the taper as did the ring set for a grey fergy rebuild. Ring 'flutter' can be controlled by machining the ring groove out to next size up or by adding a spacer similar to the old style oil ring which had a top n botton thin ring with the thicker ring with grooves in it in between.
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