TheSamba.com :: View topic - RE-heat treating stock connecting rods?

Wed Oct 16, 2019 2:01 am

I cant remember if I asked this question here or not.
Can stock VW rods be Re-heat treated to make them stronger? Does any body know what they [stock rods] are made of?
A buddy of mine who used to road race Honda's [1980's-90's] was telling about having stock rods re-heat treated and how much stronger they were, could this be done to a set of 36hp rods? He said they would have to hone the big end afterwards and put new bushings in the small end because they had to remove them prior to going in the oven, I think he said the had to heat them to 1650° and quench them in special oil.
I realize Honda rods would be made of newer steel alloy then a 60-70 year old VW rod, I am just wondering if it would work.

eQ

Wed Oct 16, 2019 5:43 am

Forged rods are generally made from medium carbon steel, that temp you mentioned is a normalizing temp, this would reduce the tensile strength and hardness, but increase the impact strength, so basically it would stretch or bend before breaking, it also relaxes the previously forged steel making it easier and more stable to machine. Its possible Honda rods are too hard and brittle for high RPM racing applications, and break before bending, it all has to do with what is done after its forged, IMHO, the material is very similar to what VW used, its all about cost, factory passenger auto engines have different needs.

Wed Oct 16, 2019 8:06 am

In order for it to work though you have to know exactly what material you have, not I think it's this or I heard it was that. I heat treat parts in the shop all the time and I'm pretty sure the VW engineers knew what they were doing. Heat treatment for strength is an exact science and I can't see making a connecting rod "stronger" without upsetting the balance. Heat treatment transforms metals to give properties such as hardness, toughness, flexibiity, tensile, impact resistance, ductility, elasticity and wear resistance to name a few. The balance between all of the final properties is the key to any heat treatment process and upsetting that balance is a recipe for disaster. In my opinion you're chasing a ghost.

Wed Oct 16, 2019 8:24 am

earthquake wrote: I cant remember if I asked this question here or not.
Can stock VW rods be Re-heat treated to make them stronger? Does any body know what they [stock rods] are made of?
A buddy of mine who used to road race Honda's [1980's-90's] was telling about having stock rods re-heat treated and how much stronger they were, could this be done to a set of 36hp rods? He said they would have to hone the big end afterwards and put new bushings in the small end because they had to remove them prior to going in the oven, I think he said the had to heat them to 1650° and quench them in special oil.
I realize Honda rods would be made of newer steel alloy then a 60-70 year old VW rod, I am just wondering if it would work.

eQ

Well, this is good out of the box thinking but kind of goes right along with one of the golden rules......."If it ain't broke, don't fix it"

There really isn't any reason to even attempt this as the connecting rods are far from the weakest link in a standard aircooled engine.

Wed Oct 16, 2019 12:55 pm

Old school guys would shot peen the rods. I've heard of stress relieving rod after rebuilding. Bake in an oven 400* for two hours.

Wed Oct 16, 2019 1:27 pm

shot peening is stress releaving.....
hell I wont even attempt to heetreet rods.....no up side to it.just get good ones...from china!!!

Wed Oct 16, 2019 3:22 pm

Actually shot peening imparts surface stress by compression. The surface is blasted with hard steel shot of a given size at a given pressure as determined by the job, the part and the material. Each ball creates a dimple thereby imparting a work hardened dimple in the parent metal. As this happens millions of times during the process it creates a layer of work hardened metal in compressed stress that encases the entire part. It's thought that stress cracking originates on the surface and this process creates a hard layer that's highly resistive to to that among other things.

Thu Oct 17, 2019 1:46 am

OK, because a couple of "KNOW IT ALL ASS HATS" over on another thread decided to bad mouth me asking a question about some thing they probably have no knowledge of, please disregard this question unless you can provide some positive feedback.

Thu Oct 17, 2019 8:44 am

earthquake wrote: OK, because a couple of "KNOW IT ALL ASS HATS" over on another thread decided to bad mouth me asking a question about some thing they probably have no knowledge of, please disregard this question unless you can provide some positive feedback.

Those 'ass hats' are some of the top VW engine builders this side of the pond. Maybe you should be open to opinions from ANYONE and not just people agreeing with you. Forums can require thick skin :D

Thu Oct 17, 2019 11:32 am

sled wrote: earthquake wrote: OK, because a couple of "KNOW IT ALL ASS HATS" over on another thread decided to bad mouth me asking a question about some thing they probably have no knowledge of, please disregard this question unless you can provide some positive feedback.

Those 'ass hats' are some of the top VW engine builders this side of the pond. Maybe you should be open to opinions from ANYONE and not just people agreeing with you. Forums can require thick skin :D

Agreed 1000%. People seem to come on the boards with an attitude right off the start. Most of what I have learned has been from right here on the samba.
Some people can be a bit harsh though.

Thu Oct 17, 2019 12:43 pm

Get em Cryo'd

Thu Oct 17, 2019 12:56 pm

Maybe you can get someone with a PMI gun to identify what alloy they are and go from there. I know Vegas Fastener Manufacturing had one...maybe if you dropped by with a present they'd check it. You would still have to deal with the fact that they will likely warp some after heat treat and need to be re-machined.

Thu Oct 17, 2019 1:32 pm

VW connecting rod feedback.....

Stock VW rods are forged from the factory and made of superior material. Just like their rocker arms, cranks, and flywheels. When machining any of these OE forged VW parts, you will notice they are difficult to cut with normal machine tools. They are much harder and tougher than a typical American made similar parts. Most other manufactures cast their cranks, flywheels, and rods. This is why the aftermarket has made "forged" parts for years as replacements for weaker cast parts.

It has been a well known fact since the early days of VW hot rodding, a stock VW rod will easily withstand 8000+ rpm in a 150+hp engine. That is more than double what it was designed to do. Vw enginers were no dummys when it came to spec'ing materials for engine parts. In the past, the OE VW flywheel is one of the only flywheels the NHRA allows without needing a blow-proof bell housing.

Just so you know.......A stock VW connecting rod is already RC35 hardness. Not super hard, but way harder than a cast part, and much tougher.

If you would like, send me a set of rods, and I will personally put them in our $20,000 heat treat oven, and I will heat treat them to whatever harness you specify. Tell me what you want them to be hardened to, and then what you would like them drawn back at, and I will do it. We can make them RC65 if you want. Don't set them down on the bench to hard, or they might shatter.

Like someone else said...The VW rod is about the last part to worry about in a VW engine. They are way overbuilt, and have been tested many many times to hold way more power than they should. Spend your time somewhere else way more productive. Like cylinder wall and ring prep, or airflow research.

Earthquake......I am sorry if I hurt your feelings. Please forgive me, and build an engine around some super hard rods. I am always up for a good experiment. :wink:

Señor Ass Hat

Thu Oct 17, 2019 3:15 pm

Some of the guns won’t read carbon. If your trying to harden a steel you need the carbon content to heat treat it. I get steel parts heat treated pretty regularly. And everything changes shape. We actually make our parts oversize then finish them after heat treatments. That would mean most likely doing both the bores on a rod and possibly straightening it. That cost alone should make a better set of rods a more attractive option. Plus unless you really know what sort of hardness your looking for you would pretty much have to experiment. It’s not a bad idea in itself. Just not really cost effective in my opinion.

Thu Oct 17, 2019 3:54 pm

Stock rods are really strong. I know I have beat on them quite hard.
I would be more worried about the heads of the rod bolts.
Get good bolts and be very picky about how much you grind off them for stroker clearance.