3400 top end on a 91 3.1L

[JH]

I have a 3.1L in a 91 lumina and i have a friend that might be able to get me a 3400. I was reading on the top end swap part of this web page and it said you can't use the same old push rods from the 3.1. But will the pushrods from the 3400 work right with the 3400 heads on my 3.1?. If they won't can anyone tell me the size of pushrod i will need to make it work? thank you for any help

[TheProfessor]

well you will need custom pushrods cause there is a difference in valve train geometry
i.e. the difference in the height of the lifters and the different rocker are ratio i think too
not sure on what size though

[v6h.o.]

You *can* get away with still using the stock 3.1L Pushrods, to this day im still running the stock 3.1L MPFI pushrods with my GEN3 top end and COMP CAM's 1.6:1 Roller Tip Rockers.

It can be done this way, however the proper pushrod length should be used to properly align the rocker tip to valve stem.

Gen3 Pushrods will not work when doing a Hybrid swap, the reason is they are too short, GEN3's use a Roller Lifter setup which then reduces both pushrods lengths by about 1/4 inch shorter.

[TrailMug]

So.. stock stamped-metal rocker tips will approach the stems at a bad angle, but roller rockers can be used to allow for some angle "fudge factor"? Hmm.. I wonder if machining the stock rockers to have a more-flat rocker-tip-to-stem contact is a sane thought.

[dbtk2]

I am using stock pushrods and my stock 1.5 stamped rockers. I've had no problems going on 3k since i did my swap now.

Shawn

[JH]

So would a 1999 3400 hvae the 1.5 stamped rockers or 1.6 rockers?

[dbtk2]

1.6. I used the stamped rockers from my 3.1. A 94 & 95 3100 will also have stamped rockers. I have '95 heads, so it allows me to use my stamped 3.1 rockers.

Shawn

[88jbody]

1999 would have roller tip rockers

[JH]

So would 91 3.1 pushrods work with roller tip rockers?

[dbtk2]

1999 would have roller tip rockers

No, a '99 would have roller FULCRUM rockers. No 3100's that I know of came with roller tips from the factory.

Shawn

[TheProfessor]

nope all were either stamped or roller fulcrom