confusion in Wayne's book on measuring rod bearing clearance

[Trakrat]

So I bought some plastigauge to measure the clearance of the rod bearing on the crank... but after I kept reading, it seems that Wayne then says that doing this will deform the bearings and can cause the bearings to spin?

So... I'm asking you all.. what is your experience? Should I just go ahead and put the rod onto the crankshaft or first measure the clearance?

Also... I have ARP rod bolts, so I'm guessing it's OK to tighten and loosen as many times as needed?

Thanks all!

[Neil Harvey]

The fact you are checking is a good thing.

Don't read to many books on "how to's" they all have their own opinions, often none based on experience. If what you are reading is written, its complete nonsense.

Too much has been written and become urban myth, it has put the fear of "God" into many reassembling their engines. Rod bolts, clearances, Cam timing etc.

There is no real set amount of clearance required. The factory give a "suggestion" of what the clearance should be. You can run clearances tighter and looser but you need to understand what and why. As most do not have this knowledge, it is best to run what the "book says". But if you are just on the upper or lower limits, or even over by some amount, as long as you understand what and how to compensate, you are OK.

As for your question, you are good to go. Don't quite understand the thought behind writing such a thing. The bearings are not made of chocolate. That seems to me to be from someone who is not an engine person nor having any experience in building engines.

Anyone with experience would tell you differently and probably tell you this way of measuring is not be most accurate. Most accurate is to fit the rod bearing shells, torque the nuts/stretch the bolts, then measure the bearing ID with a bore gauge. Then mic the crank journals and do the math. Also make sure you use the rod bolts you intend to run with and measure their free length before you start. Then after tightening and checking your clearances, you can go back and see if they return to their original length. This way you know you have not gone past their yield point. I can assure you that the torque specs they give you will not deform the bolts. Often to meet the ideal stretch length, you have to go past the torque value. This typically is because each bot/nut will have slightly different friction levels.

Hope this help. If you need further advice, you can email me or PM me. I'm glad to help.

[Peteinjp]

To be fair to Wayne- in his book he says that he does not ascribe to that idea however a “prominent” mechanic mentioned this idea to him so even though he doesn’t ascribe to it he’s just putting it out there so to speak.

[Walt Fricke]

Rat - basically all steel bolts can be reused as long as they don't exceed their plastic limit. That means that after they are stretched (by torqueing, which stretches them)they return to their pre-stretch length when unfastened and measured again. ARP has a specification for how much residual stretch is OK - I forget, maybe one one thousandth of an inch longer than when brand new in the box.

Which is why you should use a stretch gauge on ARP bolts, and keep a record of what they were new, and what you stretched them to, in case you ever have to undo them (like to replace rod bearings).

If you don't use a stretch gauge, ARP has a procedure for torqueing, but you'd take a chance reusing those bolts, as you would have no way of knowing if a bolt had exceeded its elastic limit. Porsche just said never reuse rod bolts to avoid this.

Carroll Smith wrote a book called Nuts, Bolts, Fasteners, and Plumbing. Buy it. It will allow you to sound like you are an engineer and know about this stuff. You've figured out why higher strength rod bolts are a good idea on the 3.2 crank. You'll enjoy the book.

When a rod cap is tightened in place, it changes the shape of the big end ID. I thought this couldn't happen, but others who had measured things set me straight. Which is why shops which recondition rods have to have them fastened to the spec they will meet when installed in the engine when they rebore them. Did you have the rods reconditioned? Measured? Balanced?

[Trakrat]

Originally Posted by Walt Fricke

Which is why shops which recondition rods have to have them fastened to the spec they will meet when installed in the engine when they rebore them. Did you have the rods reconditioned? Measured? Balanced?

Ollie's required me to send them my ARP rod bolts. Unfortunately Ollie's provides no numbers/documentation to its clients of any measurements, etc... They 'said' they balanced and measured everything though, and their customers just have to take their word for it.

I weighed each rod myself and it seems 4 of them are all the same gram weight... with 2 others being a few grams off.