Lower end Knock or rattle

This is all new to me so pls bear with me. My 81 Seca 750 has a Knocking/rattling noise that I have been unable to get rid of. It appears to be coming from @ the lower front end @ oil filter but I can not be certain (darn machine is a vantrilaquist). I have attemted to reset the auto cam chain tensioner (2 clockwise turns w/a quick counter turn), but noise is still their. Bike has 22k miles. I am about to give up and transport it to the shop but before I do.... Any suggestions??? Can bad gas create this condition?? AHHH we are in the waning riding days of the year - Thanks for any help

 

Bottom end knock is not a good thing.

Before you panic though - check to make sure nothing is loose or banging.

-Exhaust downpipe collars.
-Exhaust banging against frame.
-Horn loose

etc.

** Don't ride or rev it until you know what the problem is.

 

Thanks MiCarl - Exaust collars appear to be secure but I will dbl check connection under engine - Dtc

 

Is it rhythmic with the engine RPM? That would probably eliminate any external connections.

Header pipe connections/collar would have been my guess, but I'm not sure what could get loose down there and rattle.

 

Hard to say about rythm I'll guess it stays in frequency of RPM. I'll have to get a better desciption and try to rule out exhaust noise(although i hope it is the exhaust). I might add that a couple of weeks before I noticed this noise some exhaust "popping" on decelleration started. When I listen with a stethescope (long screw driver to my ear) it does not sound internal.

 

I take this bike on relatively short trips and it has been cold with high moisture in the air. I ran it last night and there is a lot of water in the pipes (steam from exhast extensive). Was wondering if this could be causing rattle?

 

ah ha - found the bolt which dampens the middle exhaust has fallen out. dampening assembly is loose (luckly I didnt lose it). Any one know what size it might be?

 

I just use zip ties and duct tape to fix just about anything. J\k I would just head to the hardware store and find a few that might be close and give it a whirl.

 

Much better than bearings!

When you go for you bolt assortment remember to get them metric

 

Got it , M10-24. I hope this stops the rattle. Also replacing diode in headlamp can and probable the headlamp relay. These little items are mucho $$.

 

Take comfort that the Lower ends are so well built that it would have taken some serious abuse to have a bearing go bad.

You need to get a length of wooden dowel and "Listen" to the engine while its running.
Probe the areas you think you hear a knock and touch the block with the long dowel. Apply pressure to the dowel and hold your thumb over the opposite end and listen to the vibrations coming from the engine.

You'll hear a knock if there is one.
If you don't ... and I'm confident that you probably will not ... check the Exhaust Collars for leaks.

Nothing is more scary to an XJ-Owner than a Exhaust Leak at the Header Collars.
The leak sounds exactly like Bigs or Main bearing knock.

You can treat the Exhaust Donuts if they aren't burned through.
I hope you find that there is just an issue with an exhaust leak, somewhere, and NO knock.

The Cycle Press labeled these engines "Bullet-proof an Hard to Kill"

Not without reason.
They are built tougher than a Ford Truck!

 

Thanks Rick

To check the collars should I back them off and inspect them? or just test with something light enough to detect a draft? The bike runs beautifully but that noise gets under my skin. Riding in cold weather is nice because my ear are covered. (like a tree in the woods) Dave

 

Inspecting the exhaust gaskets will require the removal of the down pipes. For as inexpensive as the doughnuts are, spring for a new set and eliminate them as the source of your noise.

 

You can masking tape a 1/2" X 2" long strip of typing paper to the end of a long screwdriver and probe the collars with the engine running.

Look for the paper to flutter if there is a leak.

 

Thanks Rick & Robert - Will do today dispite cold outside.. Still, no salt or sand on the pavement though. Dave

 

Yep. I can attest to that personally.

Don't tell Mike Rowe that. You'll hurt his feelings.

 

OK. stumped Again! I purchased replacement exhaust header gaskets. Remove the header collars. Loosened the camps @ lower pipes but can not budge header pipes. They are stuck on the lower exhaust real well. any trick to loosen these things? - Dtc5

 

Hard Rubber hammer. You ...
Tap to the left ...
and then you tap to the right ...
then you grab the stuck head pipe ...
and shake it all about.

If those Pipes haven't been out of there in years ... they ain't going to want to come out of there without a BIG fight.

Rubber Hammer them and get them ... moving.
Shoot penetrating oil all around the seam.
Tap them left and right and then start pulling the 12 O'Clock ~ 6 O'Clock vector until they start inching their way out.

Eventually, there will be a point that the bike surrenders and you win.
You'll have one of the Head Piped out.

That when your glad its not an 8 Cylinder!!! : )

 

Thats what I thought. Gotta go bust some knuckles. My kind of trick . Thanks Rick