quik95lt1

iTrader: (7)

Figured I'd share some machining infortmation of what replacing rod bolts can and cannot do. Theres been much controversy over the years espically on ths site pertaining to swapping out rod bolts in an engine and not resizing the journal ends. Many say its ok just do it and many say no take it apart and resize. A recent customer engine I took apart for a rebuild had ARP rod bolts put in it about a year ago and never had the rods resized. Below are the bearings from the engine.

Here is the rod cap and bearing.....as you can see there is a wear mark about .75" wide right on the bottom of the bearing.....you can clearly see the wear is fresh compared to the rest of the bearing......



Here is the bearing shell from the rod.....again notice the 1" wear mark at the bottom of the bearing again.....


this was caused by the rods not being resized and the clamping force on the new bolts being different from the original GM bolts.......the arp 8740 bolts are supirior to the GM bolts in clamping force however the effect on the rod bearing is negated by the clamping force improvement. How this happens is the housing bore is distorted by the extra clamping force, it pulls down ths sides of the cap more which intern pushes the sides of the cap outward and pulls the top and bottom of the cap/rod inward. In essence "ovaling" the housing bore, had this motor been continued to be run and not taken apart failure wouldn't have been to far in the future. Hopefully this is some clear cut evidence for anyone replacing rod bolts and questioning whether to resize the rod ends. Basically, DON"T DO IT! When changing bolts if the clamping force is different the housings MUST be re-machined. This goes for rods and mains.

Hope this info is useful!!!



Mike

toomany

I always figured it was standard practice to resize the rods when replacing the bolts. The machine shop I use only charges $12 a rod to replace bolts and resize, that's cheap enough to not even consider not doing it.

speed_demon24

iTrader: (6)

Its pretty common knowledge that you have to the rods with new bolts. only the ratards say you don't have to.

jaycenk

iTrader: (1)

question though. That I take it from using arps torque specs. If you used gm book specs would the outcome be different? I'm guessing no but I'd figure I would ask.

96capricemgr

iTrader: (1)

I can almost see this being a valid debate with capscrew rods if the new bolts are designed for the same clamping load. With pressed rodbolts I can't see any pretending it would be OK to swap bolts without resizing.

96capricemgr

iTrader: (1)

Torque specs are designed to stretch the fastener, different design fasteners have different stretch for a given torque value. If the ARP requires 10ftlbs(just a for instance) more to get it to stretch then using the factory torque is effectively leaving it loose by not stretching it enough. Does that sound like a reasonable idea?

I also wonder about bore distortion just from pressing old bolts out and new in.

jaycenk

iTrader: (1)

See this is what I was always told was anytime you repress them they should be resized. Good info with visuals though. I wont be taking either of those chances though.

ADM

I just picked up a 95' scrap yard short block to rebuild for my 94' Z28.

All the main bearings were in perfect shape, and so were the con-rod bearings except for 2 of them that had wear marks like you showed in the picture on the cap end. They were all GM bearings.

The wear marks were similar to the 1st pic but narrower, and the wear marks seemed to have some discolouration at their borders.

Machinist inspected the crank and it was clean, not a scratch. Also measured and requested standard bearings for both main and con-rods.

But I wish to install ARP rod bolts and studs as a safety measure. I spun 3 mains and 5 rod bearings on my previous short block banging the rev-limiter in a WOT failed 2-3 shift at 6500.

My machinist said they would aim for 0.0015" - 0.0020" for bearing clearances, where as I have read from searched that the bearing clearances of the stock LT1 are different in between mains and also different in between con-rods.

Seen some performance rebuilds go for 0.0025" clearance and was wondering if I should go for that.

All I run is a CC503 with supporting mods, a GMPP high pressure/standard volume oil pump and will have forged pistons as the cylinders need an overbore.

The machinist here will not assemble the block, I will have to do that myself. Picking up the How To Rebuild LT1/LT4 book to help guide me through the assembly process.

I do have access to high quality torque wrenches and also accurate calibrated precison measurement tools should I want to do things the bolt strech measurement way.

Should I install GM bearings on the rebuild or go for aftermarket? If so what brand?

Its going to be a daily driven car that will see some hammering and high RPM shifts whenever I get the chance (I drive my car hard) but never see the strip.

I want to do this once and do it right. Please advise from your experience in bulding motors.

quik95lt1

iTrader: (7)

.0015 on rods and mains is WAYYYYY too tight......i run my street motors at .0025-.0027 on rods and .0028-.0030 on mains......my race motors like mine i run .0028-.0031 on rods and .0029 to .0032 on mains......

bearings id run clevites ive always used them and have had excellent ersults....

invest in a good torque wrench.....

quik95lt1

iTrader: (7)

true this issue was on an LS1 i took apart last night which have cap screws and after seeing this issue yet AGAIN lol i figured id post up and show the effects that no one ever sees.....same idea applys to stud rods too but yes your right about the studs

96capricemgr

iTrader: (1)

Like I said I could see it being a valid debate on an LS style capscrew. I did not say I thought it was perfectly OK on them.

I have an ich to play with my Sierra so I have been doing some LS variant reading.

ADM

I was planning on using this kit as I am on a budget...if I can find some good used forged pistons and forged I-beam rods with ARP cap screws I would not reuse my current rods and the Speed Pros in the kit

http://www.summitracing.com/parts/FEM-CSMHP766-300/

Bottom end will get ARP fasteners, already have ARP head bolts for the top end.

I know the HV oil pump is not to be used, already have a standard volume high pressure GMPP pump off my previous motor.

My torque wrench is a Snap-On piece, I get it calibrated at a specialised workshop we have at work where we have a Snap-On torque wrench calibration rig.

Which assembly lube should I use?

People who are going to bash my parts list, can you kindly advise better alternative parts please.

gregrob

iTrader: (8)

This is not an issue an an LS engine if done properly... he should have used the katech bolts instead of ARPs....

BIGCAT7274

i would not use a hv oil pump. the std volume pump with a higher output psi would be safer.

Speedy

Well I resized mine when I put in ARP bolts. Some things are just better left to the machine shop.

fex77k

iTrader: (2)

I've ran clevites in my last few motors. I had to get a tech angle and a BHJ plate for an LS build. Both were a bit pricey, but they get the job done.

bowtienut

iTrader: (1)

Regardless whether you're using stock or ARP bolts, I'd resize the big ends anyway, if the engine is going to be seeing some R's.
The big ends on mine were up to .0015" out of round when we tore it down. bone stock B-body motor with only 90k miles on it; probably never saw more than 5500 rpm.

quik95lt1

iTrader: (7)

https://ls1tech.com/forums/generatio...ng-come-3.html

check this out.....i posted up this same thread in the LS1 section to maybe try and help a few people...........got all the keyboard warrior's arguing my point....and a few people actually agreeing with the solid info........ "but LS1Tech says its ok!!" .............its times like this that remind me why i own an LT1 lol

96capricemgr

iTrader: (1)

The thing is people don't understand "things we get away with" vs. "doing it right"

I understand guys get away with the Katech bolts in LS1s, that doesn't mean there is no distortion. One guy was claiming years of use on multiple engines, but he has no idea if one will fly apart tomorrow. Given the number of success stories with the Katech bolts in LS rods I think it somewhat reasonable for guys to try it accepting it as a gamble.

quik95lt1

iTrader: (7)

couldn't have said it any better myself.............goddamnit i hate people sometimes lol