Hey all,
Rebuilt my 96 heritage last year ground up, rode it a couple times before winter and ran into a problem and haven't dealt with it since. Fyi looking for information mainly. Every bearing, seal, bushing in the engine was replaced also installed a big bore kit in it with new cylinders as the old had rusted and corroded from the previous owner letting it sit.

The problem is it has a strong vibration that seems only gets stronger as I push up to 4k RPM I haven't pushed past that as the vibration is to much to handle my eyeballs vibrate so much i cant see straight, plus still in the break in period. I did not notice much at first because i kept the rpm's limited to 2.5k ish with a few local rides, then upped the rev limiter to 4k this is when i started to notice it. Did a few longer rides when I hopped on the freeway is when it really became prevalent as i was forced into the higher rpms in 5th gear.

I did not do any balancing or weighing of the internal parts. After replacing the connecting rod bearings I did true the flywheel assembly on my lathe with dial indicators and i spent way too much time getting it almost dead nuts. I am in the process of stripping the bike back down to pull the engine but i had a thought after doing some research and looking for some advice. I am not sure if this was present before putting the big bore kit on the bike as i only road it one time after getting it running after it had sat and found the base gaskets blown and really bad steering stem bearings that tired to kill me with a bad case of death wobble.

My thought i still have the original pistons i am going to weigh them vs the new and see what the difference is. If the difference is significant is is possible to trim the weight of the pistons and this would correct the problem? Part of me is trying to keep from pulling the engine and splitting the case if i don't have too. What am i missing and should i just bite the bullet pull the engine, not wanting to send the crank out if i can at all keep from it. I don't really have anyone local that can balance the crank from what i have found unless someone knows of a good shop in western Washington that can do it?

 

Did you run it with all the engine mounts loose for 30 seconds before tightening them down?

 

It is a solid mount engine no rubber between engine and frame. I am guessing you are referring to rubber engine mounts right?

 

Loosen the engine mount fasteners and transmission mount fasteners, re torque.

 

Would this really help with a vibration issues presenting at higher rpms? I mean I will give it a shot just don't quite under stand how that this will help on a solid mount setup?

 

Have you held 3-4k whilst stationary, in neutral? Did it still vibrate?

 

Always do the cheap easy stuff first when troubleshooting an issue of any type.

A loose engine mount fastener can cause a vibration, easy enough to loosen them and retorque, won`t cost a dime.

 

Which bore kit did you use?

You can try to compare piston weights but HD cranks aren't balanced (IIRC).

What else was done to the bike? Cam, ignition. Have you spent any time trying to tune the motor?

 

Another vote for out of balance because of super light (probably cast) pistons.

Original pistons are about 392 grams.

Those "kits" are low quality and most say on them "not for high performance use"

If you plan to ride it - go to a dealer and order 2 cylinder kits (they come with pistons/rings) and a top end gasket set. All that is about &1300. and you'll be in balance with original stuff.

 

The OP installed a big bore kit, so the cases have been machined to accept the larger diameter cylinders, so he won't be able to go back to the stock size 3 1/2 bore cylinders. The flywheels will need to be re-balanced if the replacement pistons are not the same weight as the original pistons. He might as well buy a 4 5/8 set of stroker flywheels and make it a 96 inch engine at this point, because he's almost there anyway.