7-bolt rods on 6-bolt crank, who's done this/knows if it will work!

[Verticaljump1]

I talked to Polk Performance and they said that 2g rods would work on a 6-bolt crank as long as I use 1G bearings. And FFWD Connection says that it can't be done, even with 1g bearings. I've called Crower (the rods I have), and crower said that it wouldn't work. The diameter of the "big end" of the rod is the same for the 7-bolt and 6-bolt, the ONLY differences are

1.) 7-bolt rods have a 22mm wrist pin, not a problem since I bought the rods with wiseco's mounted.

2.) The "big end" of the 7-bolt (1.038) rod has FEW HUNDREDTHS less width then a 6-bolt (1.115) rod.

I bought the pistons/rods thinking that I could use them, but after talking to FFWD and Crower, Idk. Polk said that they do it all the time with eagle rods, and I'd imagine that they aren't any different than the crowers in terms of specs. And the use of 1g bearings will limit free-play of the rod/bearings on the crank journal. Please let me know if you know it'll work or if you run 2g rods on a 6-bolt crank. I'm confused as hell . Polk said that they have done this before, but why did I get different answers from everyone else? I apologize to Polk if I am offending your business in any way, I'm not, I just want to make sure my motor will work.

 

[project_tsi]

I have had this discussion a few times now w/ a friend of mine.

He works at a performance store and has all 6 and 7 bolt rods and pistons in stock, however the 7 bolts are a bit cheaper in price, and the rods weighed a bit less.

We were debating just buying the cheaper 7 bolt rods and pistons and putting them on a 6 bolt engine/crank. We decided against it b/c we too found out the rods width are different and we didn't know if or if not that was useable w/ different cranks, but w/ the same bearings.

I would assume that buy using the 7 bolt bearings in conjunction w/ the 7 bolt rods would be the way to go, considering the 7 bolt rods are not as wide, so the bearings should not be as wide either, right? That way the rods can't "slide" around at all in a larger width bearing.

Or I may be wrong and the 6 bolt bearings need to be used. Maybe if you used the not as wide 7 bolt bearings in the 6 bolt crank, they run the risk of "sliding" around?

There is kind of an equal toss up on both sides here.

I am also very eager to find out what the verdict here is.

If anyone would know about this, it would be Mitch over at Engintecs.

http://engintecs.com/

 

[Verticaljump1]

BTW how's that eprom ecu working that I sold ya? You'd have to use 1g bearings because they would have to sit flush on the crank journal. You'd think that with the arp rod bolts torqued as hard as they are that there wouldn't be any slack for play. I'm leaning towards just saying the hell with it and doing it, the only difference would be less than 1/10th of an inch. And Polk approved it..., but I better wait. I bought crower rods/wiseco 9:1 pistons and that'll make one hell of a motor, I'd hate to give them up because they won't work.

 

[Big Woo]

Well I do not have both the 6 & 7 bolt rods in front of me right now, but I can verify this tonight.

Based on the information you provided the 6-bolt rod is 1.115 wide and the 7-bolt rod is 1.038 wide. That is a difference of 0.077, the Haynes manual specifies the connecting rod endplay (side clearance) at 0.0039-0.0098 for a 6-bolt motor. Therefore if your 7-bolt rods are 0.077 smaller than the 6-bolt rods, and the 6-bolt crank you are trying to use has rod journals wide enough to provide 0.0039 to 0.0098 clearance when used with a six bolt rod, then if you try to use the 7- bolt rods on a 6-bolt crank you will have from 0.0809 to 0.0868 of connecting rod endplay.

Exceeding the connecting rod endplay specification by this much will only lead to bad things.

 

[project_tsi]

Well then. Is it possible to take a 7 bolt block, and put in a 6 bolt crank, rods, and pistons? Maybe like a direct swap in, or w/ a line hone? If it is possible, wouldn't that just rule out swapping a complete 6 bolt in a 2g granted that the block is still in good shape? Or is it not possible due to the crank sensors and bottom end girdle configuration?

 

[project_tsi]

BTW how's that eprom ecu working that I sold ya? .

Its working great. No problems with it. Installed my DSMLink chip and its been working flawlessly since. Sure, it doesn't look the best, whoever put the new caps in must have had no experience w/ soldering or SMD's, but looks don't matter, its how it works. And it works great.

 

[biglady112]

Hea I told you when you were trying to buy those rods and pistons that it will work. Only if you put 6 bolt rods in a 7 bolt. We had a 7 bolt motor running 6 bolt eagle rods. We made 540hp with that setup. Just ran out of time to tune.

Take what BigWoo to heart. You can go bigger but not smaller. You can put 6 bolt rods in a 7 bolt but not vice versa. The big end of the rods are the same size, the journal width is what is difference. The pin size is also different. Just have to make sure the pin heighth matches.

Steven

 

[Spoolin4Ever]

The 7 bolt rods are weaker too, though, correct?

He just can't get his money back so he wants to do it? Cause most people want 6 bolt rods I thought because they are stronger.

 

[project_tsi]

The 7 bolt rods are weaker too, though, correct?

He just can't get his money back so he wants to do it? Cause most people want 6 bolt rods I thought because they are stronger.

You would think all aftermarket rods would be just as strong 6 or 7 bolt.