TwinCam 88 - Engine Knock
 

Hi guys,

My engine recently developed a knocking sound and I want to ask for some of your opinions about what could it be. It's a 2003 RK with a stock 88" engine + stage 1 upgrade (SE mufflers, SE air cleaner, Mikuni carb). The cam chains + tensioners were changed this summer. The engine has about 50.000 miles.

The sound is very noticeable at cold starting. Once it heats up, the intensity diminishes. Probably the oil gets to the problematic area and the metal tends to expand a bit, compensating for the problem.

My mechanic suggested I keep on riding until it gets louder, as it would be hard to track down the problem if he takes the engine apart now. He said it might be the bolt connecting the piston to the rod.

It's kind of hard to sleep at night, knowing that my baby is sick :).

Here is a video with an audio recording of the problem:

What do you guys think?

Thanks!

There is no bolt holding the piston to the connecting rod, it's a wrist pin with a clip on each side.

That said, it kinda does sound like a rod knock, maybe the other end (the big end). I guess you could ride it until it got louder or broke like your guy says but it'll just cost more money. I'd take it apart and look.

Just reaching, but it kinda sounds like an exhaust leak. Hard to tell with the video. I had a 99 flht that sounded similar. At about 95k miles, a weld cracked on the exhaust coming off the rear jug. Hope it's something that simple.

The idle is way too low. Twin Cam engines have a higher idle so it could build oil pressure.

@Next In LineNext In Line: It was cold and I intentionally left the choke half-way, in order for the knock to be more easily distinguished for the video.

@MTBIG GMTBIG G: I will look for cracks in the exhaust.

@NomadmaxNomadmax: Yes you're right about the wrist pin. Sorry for that :). I'm just not too tech savvy, nor I'm too familiar with the mechanical terminology in English.

That's OK, My Romanian is terrible;)

I'd wait and see if someone comes up with any more suggestions here. In the meantime it couldn't hurt to look and see if it is an exhaust leak as suggested by the other poster. That said, I wouldn't allow the bike to idle that low, even for diagnosis. If it isn't something simple I wouldn't ride it until it became more pronounced, that's just going to cost more money and time.

Turn up the idle and re-post. At that low speed even a bad compensator will knock like that....

Idleing too low - agree on turn up idle and see if compensator is culprit.

I would HIGHLY advise checking compensator nut for proper clamp! Seen tons of them loose after they switched to dual rollers.

I took another 2 recordings:
Cold engine at startup:

Hot engine - 20 miles of aggressive riding:

When engine is this hot, I cannot hear the knock anymore.

Unless you've had the compensator bolt re-torqued, I would look into re-torquing it.. Also trim some off the base if the nut to ensure proper clamping force on the compensator / alternator rotor. It's common problem with the 03 as they were the first year without the left side timken bearing..