99 Century engine swap

[Sportster]

I can't find a decent 3100M motor but found a nice J motor. I know the intake and plenum have to be changed and noticed the Fel Pro intake gaskets have a different part number for the two motors MS98003T and MS98004T. I believe the J has bigger intake ports. I am not looking for power, just a smooth motor for my 99 Century. Has anyone here put a J motor in place of an M. I might have to put my heads and intake on the J motor to use it. Any suggestions?

[robertisaar]

i don't see any reason why to swap stuff, it should work fine. its not any rougher of an engine. i'm not sure about the EGR, but other than that, it should be direct replacement.

[Sportster]

Yes the EGR is different, the fuel lines won't reach and P/S pump will have to be changed as well as the timing cover as the belt tensioner is located different. It would be no problem with the M timing cover and intake.

[bszopi]

You can swap the timing cover without any issue. People do the 3400 swap (identical to the J motor except for bore) to older 3100 vehicles all the time. Although not everything will apply to you, go to 3400swap.com and download the guide. That will give you some ideas of possible issues you will run into. But honestly, it is almost a direct replacement.