factory new block, high revs = rod bolts?

[PowerDubs]

Question...

I have purchased a factory new block from overseas to replace the old us spec block in my playcar. The new configuration will be with ITB's, large cams, header, headwork, etc..

My concern is that the engine will see substantially higher RPM than the orig factory intended. I was advised to replace the rod bolts with ARP. I was then told that if I replace the rod bolts that I will need to have the rods resized at a machine shop? Is this true even though the engine is all factory new never ran? I was hoping I could take out one factory bolt..swap in the ARP while leaving the other orig tight.. then swap the other...my thought being as to not disturb anything with the bearing.

Thoughts? I've seen many *many* people over the years have problems with spun bearings on this particuler engine after rebuilds, so that was my reason for purchasing a factory new engine...but I don't want to run into issues taking the stock bolts past their limits either.

Thanks- Josh

 

[MikeHalloran]

I'd _guess_ that both factory and ARP bolts are pressed into the rods, and you won't be able to change them in situ without using a big hammer. Even if you can keep the hammer from striking something it shouldn't, the shank knurls will generate chips coming out and going in, and those won't do your engine any good.

Two strategies suggest themselves: Run it with a stock bottom end until something breaks, then replace the broken stuff with something stronger, and repeat. Or, replace rods, bolts, pins, and pistons with stronger parts before you bother to start the engine.

Cheapest way: Find some of those *many* people, and ask them what they did before, and after, their bearings spun.




Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[PowerDubs]

Mike...

These are for a Vw watercooled engine, and from my understanding, they just slide right in and out.

I did a search on a VW forum I frequent and here is a post about them with both sides argueing whether anything needs to be done or not, but I figured I would ask for help over here since you guys really know your stuff and are very helpful.

http://forums.vwvortex.com/zerothread?id=1571291

 

[strokersix]

PowerDubs,

If you fabricate a special press (kind of like a bg "C" clamp or ball joint press) with appropriate sleeves you might have better luck swapping the rod bolts while the engine is assembled. This will avoid using a hammer.

A better plan is to tear down the engine. This will allow you to inspect the components and do the job properly.

 

[Tmoose]

I think I'd do my own test, on my own con rods, measuring and mapping the bores before and after changing the bolts.

Actually I have done some testing like that, and I would not change knurled bolts without resizing the rods.

I think Air cooled VDubs used to have very loose bolt>cap fits, and a certain "alignment" was part of the assembly procedure. I think it's significant that Carillo and others use dowels to locate the cap to the rod. A typical spec for a rod's bearing bore is round within 0.0002 inch. Yes, before delta wall type bearings were available it was necessary on some engines to intentionally make the rods oval to get the bearing splint line a little further from the crank. But nobody want an offset cap.It's tough to beat a round hole the correct size.

 

[EngJW]

If there is anything about the bolts that control alignment- a pilot diameter, press fit, or knurl- you should get the rods resized after installing the new bolts. You are working down to .0001 or so and it would not take much to throw them off. Also, just the operation of pressing in new bolts could cause some distortion of the bore.

Loose bolts would have some other means of alignment such as dowels, sleeves around the bolts, or cracked caps.

If you are concerned enough about the high rpm durability of the engine to replace the rod bolts, you should get all the other blueprinting operations done on the rods as well.

 

[evelrod]

Josh, you are only going to get one shot at getting it right the FIRST time. If you have the proper equipment to measure the rods (I doubt you have as most shops do not unless they do their own machine work) then, change out the rod bolts and take them to be checked and/or resized as needed. ARP torque specs often differ from OEM. What's a couple bucks to loosing a bearing.

If you are concerned enough about the high rpm durability of the engine to replace the rod bolts, you should get all the other blueprinting operations done on the rods as well.

Words to live by, IMO!

Rod

 

[icrman]

What is the size differance of factory vs after market?
Even the after market stuff can fail. All it takes is one inclusion. If the after market bolts aren't any larger diameter or stepped for stress distribution. I would live with what the factory installed. A higher hardness is not always a good thing. Do both styles have cut or rolled threads?