Hitchcocks Forum

Recently, after removing the primary chain tension adjuster and replacing it with our hosts rubber based one, the bike has developed a knocking sound. Rather ironic, as the rubber based one should cut down on any noise. I have since opened up the chaincase again, removed and put back the rotor and readjusted the chain which is neither too tight or too loose. In second gear at 20mph the knock is about once every second, and it only knocks when under load. The sound disappears when going down hills, or when the bike is stationary. There is no movement in the rotor or drive shaft, and I haven't discovered any metal filings in the oil, even after riding the bike several hundred miles with the knock. I'm wondering if this is a main bearing issue or not. The bike is an Electra X with 20.000 miles under the belt. I would be very grateful for any advice!

Robin, you need to determine where the knocking is coming from. Use a stethoscope, ha ha ha, or a screwdriver to pin point the noise location. Place the screwdriver blade against the engine, primary chaincase etc and if you put your ear against the handle it will act like a stethoscope. You ask about main bearings. They do not normally "knock". As they only have rotary motion contend with, they usually rumble if they are failing. Knocking by definition is usually a sign of impact/compessive loads such as a big end. A primary chain adjuster may create sound but again as the chain runs over the surface it is unlikely to be a knocking noise.....unless you have left something loose to flail around and strike a casing. Diagnosis by noise description alone is nigh on impossible unfortunately. HTH.

Hi Robin. Your knock frequency at 20MPH in second gear equates to an engine revs of 2300RPM approx, which works out to about 38 revs a second. If you halve that to account that it's a four stroke engine it works out at 19 firing strokes a second for 20 mph in second gear. If you apply the primary chain reduction of 2.24, you get a clutch revolution speed of 16 Revs/S or 8 revs for every power pulse. The primary chain is 90 links. The engine sprocket is 25T so the P/chain circulates at approx 10 times a second. The gearbox sprocket will be turning at 5.4 revs/S. The rear chain is 94 links long. So the rear chain, driven by an 18T gearbox sprocket turning at 5.4 revs/S will cycle round at …guess what?.... About once every second! It would seem then if your knock is at 1 second at 20MPH in second gear, the ONLY part that is repeatedly turning at that frequency, is the Rear Chain. Is your rear chain loose?

At once per second it sounds a bit like a final drive issue, have you checked the main chain and sprockets? I agree with MM though a piece of dowel or stick will give a good stethoscope effect and will at worst tell you were the noise isn't coming from,

Ha! posted just before me you've got to be quick in this forum!

As a quick double check, if its rear chain related then it will be speed depedant and not related to any particular gear, It might only manifest itself under the same sort of condition though, accelerating ,constant speed or on the over run. For a chain to knock at any one place, well sone chains have a loose spot and a tight spot although this tend to cycle over several revs but it could occur every one revolution of the chain, depending on wear. Otherwise the spring link could be catching (unlikely) ...or any one part due to slackness maybe on the chain guard or on the back of the primary case.

Robin,
Are sure the knock is only once a second? My Electra X developed a knock at about 16000 miles and it turned out to be the dreaded Electra X big end failure. It progressively got worse over a month or so and in the end, after checking everything else, I whipped the head/barrel/piston off and sure enough there was some vertical movement of the conrod. There was some metal in the oil as well, but not as much as I expected

rog you say ".....There was some metal in the oil as well, but not as much as I expected". As I have said on here before there should be no metal in the oil. So how much did you expect to find one wonders? There is only one course of action to be taken immediately, if you have bottom end knocking and/or metal in the oil..........STOP THE ENGINE. Oil and metal do not mix they cause damage. Sorry if I sound like I am shouting BUT I have seen a number of reports on here where people seem to think that it is OK to have metal in their oil. IT IS NOT. The filters in any IC engine lubrication system will just not filter out the metal. I have never previously come across anybody who even thought that metal in oil is OK.

Thanks for all the response, Guys. A wealth of ideas to take on board. I actually wrote a rather lengthy and detailed reply last night, but I apparently took too long and the message system timed out on me and I lost it all when trying to post it. So this morning just a quick message. I'm off to work on the bike this morning and won't have any time to follow up your leads. Just did a quick check of the rear chain and all appears fine. I will have time for a more detailed investigation tomorrow, and keep you updated. Many thanks!

Rog,
You won't find a lot of metal in the oil because you have a roller big end, it only trashes one side of the crank pin and doesn't need much to be noisy, it is the floating bush which puts metal everywhere and I mean everywhere