360 con rod big end bore?

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67Dart273

67Dart273

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Tore down the "junkyard" 360, which spun no 8, did not tear up the crank. It appears that the rods have been "reconned" but from the internal pattern, almost looks like some hack honed them with a brake hone, etc

I don't see in the "book" WTH is the allowable big end rod bore and out of round?
 
A quote from "How to Hot Rod Smallblock Mopar Engines" by Larry Shepard.

"The big ends ID (inside diameter) should be between 2.2500 in. and 2.2505 in. For high RPM use, it's recommended that the big end be sized two-tenths undersize or 2.2498 in."
 
Thanks. I don't know why that doesn't seem to be in the (76) shop manual. My thinking is that these rods were "backyard" reconned and the bore is too large. The rods/ bearings "have the look" to me of being a little loose, plus, one spun. It didn't seize on the crank, the crank "looks" great.

I'm sittin here with my beat up old mikes tryin to decide which ones might still be accurate, LOL I have a "stackable" 2" standard.
 
Bad Sport said:
A quote from "How to Hot Rod Smallblock Mopar Engines" by Larry Shepard.

"The big ends ID (inside diameter) should be between 2.2500 in. and 2.2505 in. For high RPM use, it's recommended that the big end be sized two-tenths undersize or 2.2498 in."
Click to expand...

Correct.
 
Follow up. Thanks for the info, here's the end of the story, or at least I hope so.

I have a total of 3!!! 360 cores, 2 of which are involved here

1..The one started this thread is the one bought running out of a junk van. I ran it for awhile and it developed a small knock. Yanked it out, dropped in a 318

This thing has been "into." The bores are great, but evidently it lost a crank. This one looks OK but has some taper, and the rods look like they were "reconditioned" by a kid with a grinder. The rod and mains show plenty of wear, all are "down to copper." Suprising, given that it's a regrind at some point and also surprising given the great condition of the bores.

2...The 2nd core is the one I paid the least for, less than a hundred bucks. The bore shows lots of wear, but the crank and bearings are "like new." Rods look great, too.

So the plan is to hone / rering the block / pistons out of engine no1

Pull the crank out of no2 and use it

Swap the no2 rods onto the no1 pistons
 
67Dart273 said:
Tore down the "junkyard" 360, which spun no 8, did not tear up the crank. It appears that the rods have been "reconned" but from the internal pattern, almost looks like some hack honed them with a brake hone, etc

I don't see in the "book" WTH is the allowable big end rod bore and out of round?
Click to expand...

A new or freshly rebuilt rod big end bore should be round within .0005 and should be straight and not tapered, hour glassed, barrel shaped, etc. more
than .0002. If the bore is longer than one inch that spec. becomes .0003. A
used rod can be as much as .001 out of round as long as it's bigger from side to side than it is from top to bottom, which they very seldom are. I hope this helps.
 
Thanks. I've got "the solution" for now, as I don't have much invested in the second block, and it would need to be bored. This is going to be a budget build. I may have to break down and invest in a set of dial bore gauges. I've got an old inside mike, but lord that thing is difficult to use.

On a side note, I could NOT FIGUREOUT why "none of this" made sense. I often "throw" my caliper in the mike to make damn sure I haven't made a great big error

Well it turns out I have a "medium spread" digi caliper from one of the "outfits" and this thing has always been "OK" for OD measurements

IT TURNS OUT that the INSIDE jaws!!!! were never !!!!! finish machined!!!!! to match the OD jaws!!!! In other words if you measure the crank with the caliper, it's within .002 or so, but if you stick the inside jaws into the mike with the same reading!!!! the damn thing is way off!!!!

These are they, and I thought they were OK until this weekend LOL

attachment.php
 
You are almost always better with used good measuring equipment, Starrett, Mitutoyo, Brown and Sharp, than with new cheap stuff.
 
I know, and agree, but I usually use this digi for "non critical" stuff and to verify readings. The whole thing is, it's pretty darn accurate for OD measurements, it's just that evidently the inside jaws were never finish machined to match the OD jaws!!!! (The jaws are one piece)
 
Ona side note - it's difficult to remove a pressed-pin piston and keep it's shape. Normally they get "squished". You may just want to reuse the whole rotating assembly rather than worry about swapping what is essentially the same piston. You're not going 110% so a little extra ring side or piston to wall clearance isn;t a big deal.
 
Plastigauge works, it could be used to test out of round too. It is still important to have the bearing fit the rod for correct crush. I like to feel the way rods rotate with oil, out of engine, tightness, or slop bad.
 
moper said:
Ona side note - it's difficult to remove a pressed-pin piston and keep it's shape. Normally they get "squished". You may just want to reuse the whole rotating assembly rather than worry about swapping what is essentially the same piston. You're not going 110% so a little extra ring side or piston to wall clearance isn;t a big deal.
Click to expand...


Actually THAT problem may be solved as well. It turns out the core block with the good rods and crank is in great shape bore -wise as well. It's looking like it will be a simple re-ring. Very little wear and taper. What I thought was a "worse" ridge turned out to be mostly carbon.

Now, wu...'d ah do wit dem 202 heads???
 
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