First Stroker Vibration at Idle

[foggybottombob]

I got my stroker back last Wed and put the first 500 miles on it. I changed the oil and filter but I have
a vibration at idle that the stock 4.0 did not have. This is a 91 XJ with the 4.6L low compression rock
crawler build. I used the Keith Black pistons dished to 26 ccs and had the combustion chambers opened
up to 60 ccs. I put in the rubber bushing versions of Brown Dog motor mounts too. So I don't know how
much to attribute the vibration to the new motor mounts.

The entire body has a rumbling resonance at idle. I had the rotating assembly balanced by the block shop.
So is idle vibration common in a stroker? Does anyone think that this resonant vibration would go away
if I change back to stock motor mounts. The idle noise is really irritating at this point and I would like
to find some way to fix this. Should a stroker have a different harmonic balancer from a stock 4.0L.
Any help here would be appreciated.

[4.whoa]

Strokers use the same balancer as stock.People have had issues with new ones being out of balance and had to get them turned. You didn't say which cam you're using but a bigger cam will be noticeable at idle.

[SilverXJ]

Did you have your balancer and flexplate/fly wheel balanced as well? When I had my new balancer done by the machine shop it was pretty out of balance. Did you follow the brown dog mounts correctly? You aren't suppose to make the center bolt too tight. If you feel the mounts are a problem call Brown Dog and ask for their recommendation. I have heard they have top notch support. I have a set of the rubber brown dog mounts to install too. Also, check out your exhaust. Make sure it isn't rubbing on anything.

[foggybottombob]

I used this camshaft. My SCR is about 8.9 so this is not a radical build. Do you think
this camshaft would make that much difference over stock?

CompCams 68-115-4 192/200 degree camshaft

[Cheromaniac]

The idle should be glass smooth so something's definitely wrong. You might want to do a compression check on all cylinders and check for vacuum leaks.

[foggybottombob]

Once the rpms get to about 1000 the engine is very smooth. It's just down around 750 or so that I get this rumble.

[Hilljack]

What type of motor mounts did you put in?

If you put in Poly (stiff compared to rubber), they will give you a lot more vibration feed back than rubber.

Try the stock units or look at M.O.R.E Off-road bombproof motor mounts if you want an upgrade.

[rpz76]

Did anyone find out what the vibration was I have the exact same issue