Crankcase Knock

[coleshere]

Hi, I'm desperate for any ideas.My bike is a 1979 gs750e.It has done 28,000 miles and never been apart.It runs and rides perfectly.The problem is a loud
knocking form the left side crankcase cover.I can feel it with my foot.It only makes the noise when the engine is under load i.e accelerating.On the stand when revved there is no knocking.I have checked/changed the rear wheel and cush drive bearings.The chain and sprockets.all the clutch bearings are perfect.All adjustments are correct.It is definately from the bottom end.Any ideas much appreciated.
Thanks Colin.

[chiphead]

Welcome to the forums. Stating where you are may be beneficial. You never know if someone is close to you and is willing to stop by and give it an ear.
A 79 750 has a roller bearing crank. I suppose you could have a bad bearing but I don't think that is common. You may have a starter clutch that is coughing up a hair ball or clutch allen screws on the back of it are loose OR a crank end nut that holds the rotor on is loose. Take the left cover off and check it out before you do more damage.

[chiphead]

Suppose it could be a rod knock on #1. Take the left cover off and go from there.

[coleshere]

Reply to Chiphead

Thanks for your ideas Chiphead.I agree with you,I doubt it is the crank bearing( I hope!).I will check the starter clutch etc.Unfortunately the bike is not at my home so it will not be until the end of September.I will post after inspection.Once again many thanks Colin.

[coleshere]

Crankcase Knock

High Chiphead,I have just checked the bike again.Sorry its been so long.I have checked the starter clutch and all is well.I could not undo the crank nut as it is too tight.I think it is going to be an engine strip.Shame really as it runs so nice.Cheers Colin.

[rustybronco]

Welcome to the forums. Stating where you are may be beneficial. You never know if someone is close to you and is willing to stop by and give it an ear.

I would do what was asked, long before you start to strip the engine down.

[supersonictoys]

does it make this noise in all gears or just 1?

[barmstro]

You have to get that nut loose and the rotor off,as it's the only way to rule out the starter clutch.
Mine made an awful knocking sound at low rpm sounded like bottom end but ended up being starter clutch .

[blowerbike]

you cant brake those engines with a sledge hammer...
its nothing serious im sure.

[SqDancerLynn1]

Does it do it at all rpm's ? Is it a knock or is it pinging ?? Have you synced the carbs. I would check the carb boots and sync the carbs. If one cyl is out of sync it can make it sound bad. My 850 would pinging andd rattle when under load, traced to bad intake boot leak.