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JP2 big end bolts

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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

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.

Diesel Engineering:
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.

Now the tapered ring makes sense going on the top groove to avoid hitting any lip that may be there.

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.

bob g


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