Machining 6-bolt Forged Rods

[Meh987]

I recently bought a GSX with a crankwalked 7-bolt. The engine came with Ross pistons and Crower rods. I'm doing a 6-bolt swap to replace the crankwalked 7-bolt. After some thorough research, I determined that I could not use the 7-bolt rods in the 6-bolt block. I know that the 2g piston/1g rod combo is pretty common, so I bought a set of Eagle 6-bolt rods. I brought the rods and pistons to the machine shop and the machinist said that if he were to machine the rods to fit the 7-bolt Ross pistons it would take off too much, if not all, or the bushing in the small end of the rod. I've searched and could not find any information pertaining to the bushing in the rods. Will machining take off too much of that bushing? Can I replace the bushing? Or should I go ahead and buy some new pistons?

 

[jspec]

Sounds like the machinist already told you the answer to this question. I believe the rods and pistons in 6 and 7 bolts are totally incompatible. On another note I may be interested in your rods and pistons if they are in good shape.

 

[JackM]

Why not just replace the bushing with the one that came in the 7-bolt rods? I would try taking the bushing out of the 6-bolt rods, get the 7-bolt Eagle rod bushing (or whatever fits), and then machine the small end of the 6-bolt rods to fit the 7-bolt bushing. Might be more trouble than it's worth, but you can use those rods if you do that... Just about any machine shop should be able to order a generic set of bushings that will fit your piston pin and they can machine the rod to fit it easy.

Shoot, if nobody there can do it, send them to me and I'll do it on my CNC milling machine, !

Jack

 

[GILZTSIAWD]

I have 6-bolt eagle rods machine to wiseco 7-bolt pistons, all in my 7-bolt block. I have run this for a good hard 2k miles with no problems whatsoever...its all in the machinist though...

 

[Meh987]

How hard is it for those bushings to press out? He told me he might destroy the ones from the 7-bolt rods when pressing them out. And also, where can I order new bushings?

 

[luvmygst]

Why cant you use the 7 bolt rods in a 6 bolt block? People use the 6 bolt rods is 7 bolts all the time. The only machining to do to put 6 bolt rods into a 7 bolt is to narrow the pin end and increase the pin hole by 1mm. If you already have the pistons and rods together then it should not be a problem. I looked at the specs for both rods and the only difference that I see between 6 and 7 bolt is the width at the pin end and the pin size.

 

[Meh987]

The 7-bolt rods will not fit on the 6-bolt crank. I don't know the exact reason why, but I stumbled upon it somewhere in the forums. I e-mailed Eagle this morning about getting rod bushings for 7-bolt rods, but they haven't gotten back to me yet. Does anyone know the size of the bushings I would need and where to get them?

 

[JackM]

Why cant you use the 7 bolt rods in a 6 bolt block? People use the 6 bolt rods is 7 bolts all the time. The only machining to do to put 6 bolt rods into a 7 bolt is to narrow the pin end and increase the pin hole by 1mm. If you already have the pistons and rods together then it should not be a problem. I looked at the specs for both rods and the only difference that I see between 6 and 7 bolt is the width at the pin end and the pin size.

The big end is much narrower on the 7s over the 6s. You can machine the big end of a 6-bolt rod down to fit the 7-bolt crank, but you can't make the 7-bolt rods wider to fit the wider bearing journals of the 6-bolt crank.

Jack

 

[luvmygst]

Thw width is the problem but it has been done, would I do it, but people have.
http://www.dsmtuners.com/forums/showthread.php?t=208641&highlight=7+bolt+rods+into+6

 

[Sharadon]

I read the other thread,, I would not use the 7 bolt rod on a 6 bolt crank. If you increase the rod end play you also increase the oil demand of the bearings. Rod end play is a factor of oil pressure and how much oil is splashed onto the cylinder(more so spash then pressure) If you have more cylinder oiling then neseccary you can overload the rings ability to control oil. That can lead to oil consumption. Also I would never use a bearing wider then the rod. Bad idea.

Pin bushings aren't that expensive, get new ones. Or, better yet. Trust your machenist. Get the right parts. Build it once.