replacing rod bolts

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abdywgn

abdywgn

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When is considered time to replace them?When the engine was cheapy rebuild the first time,I installed new rod bolt nuts from the dealer.the engine leaked oil badly from the cam plug,so the engine only had 300 miles on it.It is now sitting apart waitting for it's next adventure.And if it is considered replacement time,any tips for doing this at home?If it matters,the engine is a 73 360 from a 3/4 pick-up,has 125,000 miles on it,always a 2-bbl intake/carb,with the rebuild it got a 340 cam/springs/headers/dual exhaust.Thanks!Bob
 
You can't do it at home. The rods must be resized after replacing the bolts, so they will have to make a trip to the machine shop. The pistons will also have to be R&R'd to do this
 
68 Sedan said:
You can't do it at home. The rods must be resized after replacing the bolts, so they will have to make a trip to the machine shop. The pistons will also have to be R&R'd to do this
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Agree. Unless you plan to completely rebuild the engine leave those bolts alone.
 
With that many miles on them in a 3/4 ton truck I can almost guarantee they need new bolts and re-sized and I agree with the guys above that they have to be re-sized after installing new bolts.
 
Thanks guys!and not to start a fight or anything,but have any of you replaced them before during a rebuild?There are devices to hold the rod and cap together while torqueing the bolts...could you use this to replace the bolts?Or-leave them on the crank and tap one out at a time,reinstalling new ones as you go?The engine is apart at the moment...guess I should measure the id of the big end,get bearings and install on crank,do the bolts one at a time and torque them up.Then remove and remeasure the id.IF I start giving stuff to the machine shop to do,then I'd put in new rods,which means new pistons and boring the block.'Course then you may as well throw in a 4.00"" crank which means better heads...so you see how this all snow balls!Bob
 
When you press them out and press the new ones in it can/will distort the bore of the big end hence the need to resize.

When I built my engine the machine shop wanted $25 each to replace the rod bolts, resize and balance them plus the cost of the bolts. Also, it's not much point in doing it if you aren't going to go with a better quality bolt.

FWIW, it was cheaper to purchase Eagle SIR rods than to rework stock rods and you wind up with a stronger rod, more closely matched weight wise, balanced rod with floating pins.
 
dgc333 said:
FWIW, it was cheaper to purchase Eagle SIR rods than to rework stock rods and you wind up with a stronger rod, more closely matched weight wise, balanced rod with floating pins.
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Not to mention the newer more modern rods are lighter. Less weight means engine will rev quicker.
 
Does anyone really think those bolts in there now are going to break? Steel doesn't wear out unless overstressed. That will break it, but it won't wear out like aluminum, which is why aluminum rods need replacing and steel rods don't.
 
Its not an issue of them wearing out but if you are modifing the engine with plans to rev it past the factory redline then the additional stresses can cause them to streach which can/will result in the nuts coming loose and/or the bearings/journals taking a beating.

Also, if the bolts have been stretched enough to yield them then the cross section has been reduced and they can't produce the same clamping force as before resulting in the first paragraph.

You have to remember that as much as the engineers would like to have designed the engine to live at 1000 HP the marketing and bean counters would have had their heads. So, the engines were designed for the target HP with an appropriate safety margin. The lack of finite analysis tools back in the day how accurate were those safety margins? Then increase the power with other changes any you can easily exceed the strength of factory parts.

Then factor in 30-40 years of unknown history of possible abuse it just makes sense to replace the two most highly stressed fasteners in your engine (rod &main bolts) and take advantage of 30-40 years of technology advancement with high quality fasteners for the rods and mains.
 
Point well taken, though the rod bolts he has now if simply reused in a low stress engine will not have to be replaced. It's a low mile rebuild and there fine.
 
The Eagle SIR rods are the units I would use...if boring the block,replacing pistons,so and so forth.I can see where pressing bolts in and out will distort the rod...which is why I'd consider measuring before and after.It's possible they may be out of round now.My thinking on bolts breaking is the rod bearing/crank journal clearance is too great.the extra movement in that area could stress the bolt even more,not to mention the rod where the bolts attach.So,what this was leading up to,I forgot.Anyway,I will use new nuts again,keep the rpm's below 5500(hyd cam),and try to remember there are cast pistons in there with some miles on 'em.Unless of course,I find a bag of money in the street and get a reward.Thanks again!Any other thoughts?Bob
 
It's not the pressing. It's the torquing. Steel does have a certain fatigue life. So replacing them does make sense, and I always go better, not more stock ones. But any change, even in brand of stock type bolt, will not load the rod cap the sae. The bore distorts, and the bearing is compromised. Sometimes guys do this without knowing and have it work. I've never seen it, but I'm sure someone has. I'm also sure I would rather run copper-worn bearings in factory high miles rod bolts before running a new bearing an new bolt without resizing.
 
What will happen is a bolt will stretch. This will allow a nut to loosen. When that happens it will back off and, if you're really lucky, the cap will get pealed open and (basically) flat on the down stroke. That will (probably) break off the other bolt and wedge the rod between the block and crank.

don't ask me how I know
 
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