Technical Do you measure rod bolt stretch or just torque?

On a rebuild, do you replace the rod bolts? With new rod bolts, do you resize the rod bearing end? Then, on installation, do you measure rod bolt stretch or just go with a torque reading?

 

how serious are you building : stocker or serious HP? on a stocker its OK to just torque, but on a serious HP it might just be a good idea to measure stretch!! just saying, Your choice....

 

Bolt stretch is far more accurate but as said not necessary for the majority of engines.


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Press in style, new bolts..Always re-size . Cap screw type, (for instance on a Buick) , you might get away with not re-sizing, but I still do it.
May not have to be replaced on a rebuild. It depends on what you're doing.

 

I’m a believer in changing the rod bolts during a rebuild


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Rod bolts are cheaper than block windows.

 

I use ARP bolts, resize, and an ARP stretch mic.

 

It depends....but if I want to make some suds and make it last, resized or new rods with new bolts, and tightened as the instructions suggest, is the way to go.

On old junk I'm just getting running again, I'll put the old bearings back in if they're not worn much, and torque the nuts to spec, and not worry about it.

 

If it's a common engine and they are available, aftermarket rods are about the same price as reconditioning and they come with new bolts. I purchased a rod bolt stretch gauge but could never get comfortable with the procedure so I went back to using the torque spec. A good torque wrench is a must and I torque, loosen, and re-torque new bolts three times. If you do replace the bolts on old rods, they must be reconditioned.

 

My son has a late model car that spun a rod bearing so I made the mistake of offering to rebuild the engine for him.

I knew it would be mean getting all New Bolts for everything but I did not realize that there was not a car dealership in the USA that stocks the bolts that were needed. I tried ARP and they did not have the bolts either.

It took 6 weeks to get the bolts from Japan and then have them shipped to somewhere in New York for proper testing for strength and length.

When I asked the guy's at the car dealership why that don't stock these bolts that told me they do not rebuild engines anymore!
I then asked them what they do when a customer as this same problem and they told me they sell them a New Crate engine and then charge them between $1,000 and $2,500 to install it and setup the computer to except it!

Long story short I was sorry I ever volunteered to rebuild my son's motor because his car sat in my shops for months while I waited for parts to come.
Because it was a dual overhead cam motor it had to variable cam timing adjusters and only one them was bad so I ordered one new variable cam timing adjuster which cost almost five hundred dollars.

Eight months after rebuilding the engine the engine would no longer fire up so I checked the timing again and this time it was off by 21 degrees which is the exact about of timing that the variable cam timing adjustments can swing each way so I had this funny feeling the 2nd car adjuster had let go.

When my son said dad are you going to take the motor apart again I said NO !!!

Rebuilding motors today is not like it was years ago for sure!
Jimbo

 

At the cost to have an old set of rods checked, resized and have ARP bolts installed, new SCAT rods are a wash, maybe even less expensive. I do whatever ARP or SCAT tells me to do for installation and torque and call it done.

 

Of course if you're building an engine for a traditional car, you have to resize the rods on an old Sunnen hone, re use the bolts, torque them instead of measuring stretch, etc.

And this method still works.

Don't buy chinese rods just because it's easier.

 

Working at a GM dealer in the parts dept, I sell a lot of engine parts (most warranty). rod bolts for most late-model engines are required to be replaced. During installation they're torqued by degrees...stretch? Hell, I dunno. But bolts (even high-end bolts) are affordable enough to replace.

 

It's hard to measure the bolt stretch on stock bolts. The arp bolts are made to work with a stretch gauge for accurate readings. The ends are machined to be able to repeat the measurement from one bolt to the next. A standard caliper or mic wont work right.

 

If your just rebuilding anything close to stock,low buck,best to have a engine that has never been rebuilt,that has not been over heated or blown up. Look good an close,as your taking it apart,it will talk too you with how the parts look. Used bearings tell you a lot from how they look as dose other parts about how even things have worn. Rods that are even across are good,same goes with mains about line bore if needed,look at them. Rod bolts an nuts,if your playing low buck n close to stock,need to be looked at,never turn a nut over when replacing it on a bolt. So much is done that is not needed,but you need to look, Play a big HP game,go with $ new.

 

Modern bolt tightning is by degree, one tightend the bolt to xx torque and then a small degree wheel socket is placed on the bolt head to be rotated xx number of degrees. But the spec on degrees has to known from the bolt manuf.

 

The big end gets resized if it needs it. If I have money I replace rod bolts and they are stretched too far yes they get replaced. On most of our old motors it is just a given that they are stretched but I never replace anything that does not need to be replaced.

 

MANY..."high end"/race type rods that use cap screws rather than nuts and bolts, have a closed off "hole" at the threaded end, so the stretch method of measurement is not possible.

Mike

 

So then just torque?

 

And obviously motors today are not like they were years ago.

 

i actually have this ARP rod bolt stretch gauge , i have never used it and probably never will

https://www.summitracing.com/parts/arp-100-9942

who has a need for one? if you can use it let me know

 

Yes, and even if they did, the rotation of the fastener itself would make getting an accurate reading very difficult, if not impossible.

 

Great responses. Guess times are different from rebuilding those motors, like say, back in the 60's. Back then, did the machine shops replace the rod bolts before honing the rod big end? Even finding an automotive machine shop these days is challenging. Those old motors would maybe live without new bolts when the horsepower was well below 500hp.

 

i don't remember changing rod bolts until the mid 90s?

 

In your estimation, what has changed since the 90's? Horsepower?

 

Perception a lot of what we do now that we didn't do has to do with marketing. We have been told that you must check rod bolts for stretch and then if they don't fall within a given range and we do what we have been told.

Obviously 60 (OK 50 LOL) years ago if the rod bolt would not tighten down far enough to give us our desired clamping pressure we changed them. If they would tighten down and hold the rod cap securely we were happy. Today we are often not as well versed in what will work and what will not. So we take the advice of those who make those decisions for us.

 

The beauty of quality aftermarket rods is that the cap is doweled to the rod. It registers perfectly when new and again if it had to come apart. Some stock rods have to be machined to accept a better rod bolt.

 

yup...times change, and mostly it's in our minds. In 1965, igniton points were fine for just about any car. Now you just gotta have electronics, because apparently points don't work any more...?????

 

In 1992, I was doing a rebuild on my nephew's '65 421 Pontiac. I had the rods rebuilt at a known engine rebuild firm in Modesto...and all the needed machine work.
This engine had been 'overhauled' by a P.O.'s Dad, ("Chevrolet mechanic for 37 years") He said it often.
Long story short: No oil pres. when cranking, 4 psi when cranking oil pump below dist.
Removed pan, all the con rod nuts were loose. I mean 3 threads loose!

Tore it down, had machine work done. Got parts back, rods rebuilt/new bolts.
I hang a crank in a fixture before assembly, and hang rods with new bearings on rod journals. (old 356 Porsche tech) Some of them bound, when torqued...some were 'loose'...Plastigauged them, specs were all over the place.
Took the rods back to Modesto, (40+ miles!!!) talked to the owner, he walked back with me to the machinist...asked him to go thru the Sunnen steps...
He clamped a Chevy rod in the vise, ground the surface; assembled the rod, but instead of torquing the nuts? Just 'secured' them with a Snap-On 3.8" drive breaker bar, 12" long. THEN he went to measure and hone.
The owner took him aside, talked to him, and said "I'll do your rods again, I still run this machine..."
I waited. When I got back with them, did my 'Porsche Rod Tech' and they were excellent.
(finally!) Two more idiots out of my life that don't understand 'circles'!

 

We could make a list as long as your arm. Some changes are valid and some defy logic. Our mind set changes and myth overcomes experience.

End of the day replace what needs to be replaced, do things the way you have been doing them for 40+ years (including *Mike's dangling rods test, if that works for you) and motor on down the road.

* @Atwater Mike I have not heard of anyone doing that with the rods and crank in a very long time. It is a good way for a quick check of your machine work, even if you are the machinist.