engine noise

I have a faint engine knock that just started. The bike runs excellent and has been well maintained. Any suggestions??

 

I'm fairly new and unfamiliar to these bikes so any advise would be appreciated. Here she is.

 

What you may hear is the lifters. They do make a distinct sound thay may be taken as engine knock. But being as we can not hear it that may not be the case. Where is the noise coming from? That would help. Upper engine, lower engine, front of the engine, rear of the engine, middle of the engine, near the ? Details... Hopefully it is nothing serious.
Also in your profile information you should put in your bike info. I would guess you have a seca 750 but can't be sure your picture is fuzzy.

 

It's an '81 SECA 750 and the noise is near the front of the engine near the exhaust port. Not sure if it's a lifter- I hope it's nothing serious but all I can think of to do is get a professional opinion or wait til the noise gets a little worse ( hopefully not stranding me in the process).

 

How many miles on the odo? is it a knock or a rattle?... does it change with load or rpm?

wouldn't hurt to record a video of it knocking and post it on the youtube or vimeo or someplace... maybe someone here with a keen ear could point you in the right direction.

could be something minor like an exhaust leak, loose valve or cam chain..

 

Very pertinent question, and we could use some history on the bike.

It most likely IS one of the simple items listed; all are common occurances.

 

Thanks alot guys- I'll get a sound clip asap. It seems to only make sound while idle. The instrument cluster has been changed so I'm not sure of the meleage. And I have recently changed the 4-1 exhaust back to the stock.

 

Soak 2 towels and wrap them around your exhaust, half off the ends.
This absorbs all exhaust sound. They won't burn.
you'll be able to hear the motor only.

 

*ding*ding*ding* Good possibility alarm***

Did you replace the gaskets between the head pipes and the head?

Also check the EGA port plugs ("drain" plugs) on the bottoms of the pipes.

 

Towels, Interesting...I have a noise also. I am pretty sure it's in the stock exhaust, maybe baffles rattling. Intermittent at idle, always noisy when I engage the clutch and give it gas, goes away around town speeds but on the hwy it is there again. The problem at 60+ mph is wind noise as I try to listen. Wrapping the mufflers may help isolate the noise.

Anybody had exhaust experiences to share that cured the noise?
(Not to steal your thread John, maybe we both get some info.) Greg

 

The stock headpipes hare double walled and have been known to crack. I had the same experence with my XJ700, it drove me nuts trying to find it. It sounded like the engine was coming apart. It ran fine otherwise. I had to remove the exhaust and tap with a rubber mallet to isolate it.

 

Yes my system is stock and I had no idea about the double walled head pipes. Thanks. My collector has rusty exterior and dented. Any trouble- shooting comments about that.

I PMed chacal for stock replacements and will check his recommendation. I have slightly looked into replacing the entire system. a quick search appears that the aftermarkets are going to be louder which spells rejetting. I do not want to rejet. Any ideas on replacement systems.

 

I did what ya said with the towels and I'll be damned. It's leaking-so I tightened the bolts and spent the time to go through and tighten any loose bolts and problem solved. It's a relief to know that it's not a piston or a lifter. :wink: l. Thanks guys.

 

Neat trick using wet towels on the exhaust. I'll have to remember that one.

 

I found no "gasket" on the 4-1 just "shims"- didn't think that was necessary. It fit well and the performance was improved 100 fold by the change so I went with it.I guess I'm learning?

 

The shims you found are actually crushable gaskets. Buy new ones at the dealer and torque the headers down to spec and the seal will be complete. An exhaust leak often sounds like a knock in the top end. The gaskets are not too expensive, likely $4 - $6 ea.

 

the gaskets are probably there, pounded into the head. Quite often there don't appear to be any, they're so hammered in they have to be dug out.

There should BE gaskets between the pipes and head, they're a crush-ring type and will prevent further leaks from developing.