Torque specs - conrod 1930-31 Nash 8

Old28 · October 30, 2013

We are rebuilding a 1930 Nash 490 Straight 8 engine, new white metal bearings having been poured and we are readying to start putting everything back in and on the block.

We really need the torque settings for tensioning the nuts on the connecting rod and main bolts.

Hoping someone has these specifications for 1930 - mid 1931 Nash Straight 8 engines.

The 1946 National Service Data book has the torque specs for 1935-40 Nash, maybe someone has a pre-WW2 edition or some other workshop book that lists this data for 1930-31.

Thanks

Old28

Owen_Dyneto · October 30, 2013

Factory-recommended actual torque specs were pretty much unheard of that early, factory and field mechanics were generally instructed by "feel". I hope someone can give you a firm recommendation but based on other engines of that era I'd think about 35 ft-lbs is typical.

Old28 · October 30, 2013

Factory-recommended actual torque specs were pretty much unheard of that early, factory and field mechanics were generally instructed by "feel". I hope someone can give you a firm recommendation but based on other engines of that era I'd think about 35 ft-lbs is typical.

Thanks Owen, The engine rebuilder we are using is very cautious, hence my query on the Forum. He has not done many engines like our Straight 8 Nash before though he is widely respected for his skills with post WW2 engines. We chose him because he is so careful, doesn't rush in but queries and thinks everything out, his is a very small family owned workshop and he is prepared to take the time over our engine, which we really appreciate. Will see him today and discuss your comment.

cheers

Old28

ply33 · October 30, 2013

Factory-recommended actual torque specs were pretty much unheard of that early, factory and field mechanics were generally instructed by "feel". I hope someone can give you a firm recommendation but based on other engines of that era I'd think about 35 ft-lbs is typical.

At least for Plymouth, I haven't found factory specified torque values earlier than around 1934, 1935 or 1936. Seems pretty standard in the factory service manuals by the late 1930s though. So I'd have to agree with Owen_Dyneto on this, you are unlikely to find official factory torque values. It seems that a good mechanic was simply supposed to know by feel how tight to go on each bolt.

Use of strong speciality steels for fasteners was in its infancy too, so you are likely looking at "grade 0" bolts. I'd check a machinist's handbook for recommended torque values based on fastener diameter and thread pitch and go from there.

Owen_Dyneto · October 30, 2013

Although it's often a good reference, I would NOT arbitrarily go with torque values recommended based on the diameter and thread pitch for connecting rod bearings without some other source data. Even back into the teens rod bolts were generally special hi-grade bolts and capable of more torque than should be used - it's a matter of too high a torque distorting the bore of the big end.

What you might do is measure the thread diameter and diameter of the connecting rod throw and with them as reference go to later makes and models to see what torque they recommend. Just by way of reference, Packard recommended 45-50 for insert bearing connecting rods in the middle 30s though I know of rebuilders who recommend about 10 ft-lbs less for the poured bearing variety though of the same rod diameter and bolt size.

Nash in the mid 30s and later seems to have specified 55-60 for all models except the Model 40 for which they specified 27-30, source is Motor's Manual.

I hope all of this is of some help.

Edited October 30, 2013 by Owen_Dyneto (see edit history)

Old28 · October 31, 2013

Ply33 and Owen,

Have just spoken with the engine rebuilder and passed on all your comments which he and I are very grateful for, appreciate you both taking the time to respond to my query. Can't help thinking how much easier sharing information and ideas is in our hobby now, when we got the Nash in 1968 we had to wait anxiously for air mail letters and parts parcels for 3-6 weeks from fellow Nash restorers and antique car enthusiasts, now it's a matter of hours!

As someone who has collected auto manuals, factory and after-market, for nearly 50 years, I was not expecting initially to have difficulty in finding the spec.s in my own collection of books, but having never had to locate this information before for any of our other cars I hadn't realised that factory torque spec.s before 1935 was going to be a problem, but not one of about 8 original mechanics and engineers books for 1920-1934 cars had the spec.s we needed. Hence me throwing the query out there on the AACA and NCCA Forums.

I have had a couple of responses too over on the Nash Car Club Members Forum - looks like the most common tensions suggested all round are in the range for Rod Bolts 35-45 lb ft and Main Cap Bolts 70 lb ft.

Engine rebuilder has taken all the comments on board and we are again underway, deadline for the block to be back in my shed for putting back into the car is December 1st - giving my son, me and a small group of vintage car club friends the Christmas school holidays to get the car back on the road.

Old28

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