3900 Cam bearing spacers

[95Grand-Am]

A while back I was talking to someone that was going to replace a 3100 with a 3900. He said that he had to put rings on a gen 3 cam to make it fit properly in the 3900. He said that the rings that he used, had to be heated then they would slide over the bearing journal and when they cooled they fit tight. Just like a ring gear on a fly wheel. Does any one know where I could buy a set of these.
My plan is to put the 3100 timing cover on the 3900. Then I would use LX9 heads and intake that way all of the older accessories should bolt on no problem. Basicly it would be a big bore LX9.

[Joseph Upson]

A while back I was talking to someone that was going to replace a 3100 with a 3900. He said that he had to put rings on a gen 3 cam to make it fit properly in the 3900. He said that the rings that he used, had to be heated then they would slide over the bearing journal and when they cooled they fit tight. Just like a ring gear on a fly wheel. Does any one know where I could buy a set of these.
My plan is to put the 3100 timing cover on the 3900. Then I would use LX9 heads and intake that way all of the older accessories should bolt on no problem. Basicly it would be a big bore LX9.

It would probably be better to use cam bearing spacers from CNCguy or have the camshaft journals resized, I believe that would be the most dependable route. You can place non 3900 heads on the block but I would not advise it due to the change in location of the combustion chamber relative to design, the earlier heads are also a little smaller in surface area not to mention what you would be giving up going backwards in airflow capability. The valves wouldn't be in an optimum position relative to the bore either. It's about the equivalent of placing iron heads on a 3400 in place of the aluminum heads.

[95Grand-Am]

Yes your right about heads being a down grade. But according to the flow chart it realy is not that much. Are you saying that they changed the bore spacing or widened the block? I'm not sure what you mean. Does the CNCguy have a web site with his products in it?

[IsaacHayes]

Yeah bore spacing changed IIRC.

[ForcedFirebird]

4mm change. I have several pics of the 3900 head gaskets on 3500 head and vice-versa.

Unfortunately I lost the data the was used to CNC "torque plates", but I can tell you the 3500 head gaskets overlapped into the chambers on a 3900 much like 3500 heads do to a 3100.

EDIT: Isaac, it is actually the rod to crank centerline was moved south. If you used a straight edge and put them in the centers of the 3900 bore, they would touch well below the crank centerline, whereas the early 3500 and older engines, the center of the crank and cylinder bores would meet.

[IsaacHayes]

Ah that's right. So technically it's not a true 60* anymore?? A little bit greater...?

[95Grand-Am]

Do you have the pic posted somewhere? Thank for all the info.

[SappySE107]

Ah that's right. So technically it's not a true 60* anymore?? A little bit greater...?

Its still a 60V6, the angle didn't change. Yeah this thread is old as dirt....

But I wanted to post this link to the spacers.

https://www.wot-tech.com/product/lz4-lz9-cam-spacers-for-vvt-delete/84