Factory rod bolt, over-torque?

LeakProof · 12-11-2009, 06:11 PM

Hey guys,

I accidentally over torqued one of my factory rod bolts to probably about 45 ft lb.
About 5 ft lb more then I was striving for.
So you think I should just loosen up on it and call it a day, or would this be foolish?
Perhaps I should just go ahead and order one or probably two more bolts (minus the nuts), for even torquing (both sides, 10,20,30,40 done).

Any suggestions would be great.
Thanks,

Leakproof.

LeakProof · 12-11-2009, 07:15 PM

Well guys,

I just went ahead and ordered two new bolts from our host.

Better to be safe then sorry.

Thanks,

Leakproof.

88-diamondblue · 12-11-2009, 10:50 PM

Good choice as they are one time use only. Peace of mind after it is all back together.

sc_rufctr · 12-12-2009, 12:18 AM

It probably would have been OK but....
Considering the cost of two new bolts it's better to be safe than sorry.

BTW: I would have done the same.

LeakProof · 04:56 AM

Thanks guys,

I really, really appreciate the feedback @ this stage in the game.

Probably not wise to take a risk with those potentially snapping bolts.

Leakproof.

chris_seven · 12-12-2009, 06:28 AM

The standard torque figure in the manual states 50Nm which is about 36 lbft.

I have been curious about factory rod bolts for some time.

The early 1968 Workshop manual clealry states that the rod bolts are 'malleable' and must be replaced at every general overhaul which is a very odd statement.

From 1972 when the length of rod bolts seemed to change; this statement has been deleted and there is no mention of replacing rod bolts from then on.

Wayne's book clealry states that rod bolts stretch permanently when torqued and must therefore be replaced at every rebuild.

I wonder if anyone has measured a rod bolt with a stretch gauge before and after use to see how much plastic deformation occurs.

I must say that I don't like this type of fastener in a con rod application as the yield strength of this type of material is not particulalry high and I can imagine that the preload must be very close to the fatigue loads seen by the bolt in service.

I would be much happier with some ARP or similar bolts correctly lubricated tightened with a stretch gauge.

This will ensure the correct preload and help the rod bolt to avoid fatigue failures.

I would think the average rod bolt will see somewhere between 10^8 and 10^9 fatigue cycles in its life time.

TCallas · 12-12-2009, 06:48 AM

LP, This is a no-brainer, you made the correct choice by deciding to replace the questionable fastener/s. Chris, I agree the ARP fasteners would be a better choice but require a bolt stretch gauge for proper installation.

Tippy · 12-12-2009, 07:22 AM

Never loosen a bolt once torqued. Over-torque is better than a tightened fastener which is then loosened.

This is aviation guidelines I'm referring too.

ix0ifan · 12-13-2009, 11:24 PM

Quote:

Originally Posted by Tippy

Never loosen a bolt once torqued. Over-torque is better than a tightened fastener which is then loosened.

It is common practice to torque new fasteners, that can't be tightened using stretch gauges, two or three times to burnish the threads to eliminate the effects of surface finish on stiction.

The amount of stretch that is produced by a given torque can vary by a much as 2 to 1 when new fasteners are 'excercised' in this way.

With any critical fastener it is common to use an approach that determines the 'nut factor' K which removes the torque taken to run the nut along a thread.

The underhead friction is also an important factor and nust with serrated flanges have a significant effect on clamping loads.

DIN 946 provides a detailed methodology to determine these factors.

I must say that I don't t feel that using overtightened bolts is a good practice.

LeakProof · 10:08 AM

Thanks again guys,

I should be more specific, My final torque is actually 39 ft lb and not 40 ft lb.

I decided on 39 ft lb, with bolts & nuts pre dipped in Marvel Mystery Oil.

3- brand new Craftsmen torque wrenches, for accuracy (didn't help on the over torque).

Wayne's book, step 1- 14.6 ft lb/ step 2, 90 degrees +/- 2 degrees.
Do not have a degree gage and was advised that this was not necessary.

Service Manual states a torque check of 50-55nm (37-41 ft lb). 37+2 = 39.

Performance Handbook states: 37-40.5 ft lb with mixture of moly lube & motor oil.
I Was hesitant on doing this because one guy on this site was snapping all his rod bolts with this type of lubricant method.

Also I was told by a Porsche engine builder that factory bolts are fine for street use.
My race car buddy disagrees saying these rod bolts are the weakest link. But I'm not racing.

Also I believe, an expert P-builder who contributes to this site uses the 10,20,30,40 ft. lb. alternating torque method.

Thats how I came to these conclusions, hopefully, I'm not screwing up to bad.

Leakproof.

robmog · 12-14-2009, 09:46 AM

how can you use oil in combination with the red locktite?

LeakProof · 10:14 AM

Great question Robmog,

I, in-fact, asked this same question. You can't. So therefore... simply put...

You don't need to use red Loctite on the rod bolts. I didn't recall seeing any Loctite on the old bolts upon removal.

But I will put a dab on the 9-flywheel bolts when re-installing.

Leakproof.

robmog · 12-14-2009, 01:27 PM

i have now officially freaked out.
as per waynes rebuild book, i torqued to 14.9 ft/lb + 90.
i used locktite not oil.
the nuts were pretty tight at + 90.
they all "dropped" evenly when the crank was tipped, and now my case is sealed.
i have to say it was uneventful, but now i'm wonder if i'm under torqued!
i saw that extensive thread about wet vs dry torque. it seems to me the issue was unsolved.
should i open the case and do it again?
its only money.

LeakProof · 03:19 PM

No, in my mind your as good as gold.

My interpretation is that you can do it either way. Also Loctite, I believe is rated as a lubricant.

Believe me, I'm freaking out my self, and haven't even closed the case yet.

I'm sure your fine.
I just hope I'm fine also.

Leakproof.

Tippy · 12-14-2009, 03:21 PM

Quote:

Originally Posted by ix0ifan

I must say that I don't t feel that using overtightened bolts is a good practice.

I failed to say it is better to end the torquing in the tightening direction than the loosening direction.

robmog · 03:32 PM

may your case be leakproof

LeakProof · 04:04 PM

I agree Tippy,

I think that one of the reasons I screwed up the over-torque was by doing it on the flywheel because #3 top bolt was @ the bottom, next to the flywheel (well one up). I honestly didn't feel the wrench give in, in that awkward spot.
I think if I had a crank holding device like the pro's it may of been a different outcome.

This must be how you gain experience.

Leakproof.

LeakProof · 04:01 PM

Robmog, I'm rite behind you. I'll be sealing up Friday.

What was your sealing method of choice?

I'll tell you my method if you tell me yours?

Oh, and thanks for the kind blessing. One can only hope these engines can one day be.. Fully-
-Leakproof.

LeakProof · 04:57 PM

Oh, and i don't know about your building facilities, but it kind of resembles my building facilities, which is a concern i have, because it's in my basement!
I'm really not sure how far to go before it's impossible to carry out?

Sure is warm & cozy next to the boiler though.

Leakproof.

mca · 12-14-2009, 06:54 PM

Quote:

i have now officially freaked out.

as per waynes rebuild book, i torqued to 14.9 ft/lb + 90.

i used locktite not oil.

the nuts were pretty tight at + 90.

they all "dropped" evenly when the crank was tipped, and now my case is sealed.

i have to say it was uneventful, but now i'm wonder if i'm under torqued!

i saw that extensive thread about wet vs dry torque. it seems to me the issue was unsolved.

should i open the case and do it again?

its only money.

I did the same method last year. Actually had a hard time making the full 90 degree turn - probably only hit 80 degrees.

9000 miles later and tons of 6000 rpm + revs ... still fine.