Rod bolt information.

[ole4]

Met with a ARP tech at the lucas drag races this weekend and was asking him about bolts vs studs. When he switched the conversation over to rod bolts I learned a few things that were the opposite of what I believed, He gave me a tech book that had all this information in it and I have copied the 3 relevant pages for anyone interested. The first page talks about rod stretch importance which in our case on clones cant be done on the rod bolts. But what I found out most interesting is the effect of various lubricants on the "friction factor" There is a chart on the second page showing the various psi's exerted on the rod bolt when torqued to the correct valve. What stood out to me was the fact that final rod bolt stretch requires a number of re torques as the first tightening will fall short as the bolt burnishes the threads creating false friction. Anyway I am going on too long here are the pages in case anyone is interested.

 

[EVOL Tweety Bird]

Really good info, things most don't even think about as they assemble an engine. You should see what I go through explaining to so called mechanics, when I tell them that they have to replace the head bolts on stretch type set ups. Or why the head gasket blew on their recent build because they didn't use the new bolts. There is a method to the madness.

 

[Havasu Dave]

Really good info, things most don't even think about as they assemble an engine. You should see what I go through explaining to so called mechanics, when I tell them that they have to replace the head bolts on stretch type set ups. Or why the head gasket blew on their recent build because they didn't use the new bolts. There is a method to the madness.

I brought this up, specifically ARP and bolt stretching a few years ago here. Crickets chirping. We used that method to assemble drag race engines. (Cars not lawn mowers) ARP has several fixtures for that they love to sell.

Speaking of which, I noted their snake oil thread lubricant. Maybe it's cheap at the NHRA events. LOL! I've been using "bolt paste" for years, always when steel goes into aluminum just for galling even if I am not torqueing. Makes everything I touch for the next hour silvery unless I remember to wash. We had a discussion on bolt lube and torque here as well. I didn't want to mention any of this to Ole, and steal his fun, but there you have it.

Ole, it gets real interesting when you come across vendors selling metallurgy as partial lubrication solutions. Way better than the Amsoil displays. But then I'm always trying to see someone famous start an engine, or snagging one of the Force women's T shirts to get too busy with vendors.

By the way, this gets moot with the two strokes. They're using 320,000 PSI Rod bolts now, twice even in the race engines, instead of the 180,000 PSI bolts. (One time use) These engines are turning a lot of RPM, but bolt stretch is moot really in small gas engines.