I thought HondaMan might be able to answer a 46 year old question that has been bugging me.
When I bought my '76 750K new, after a short time (days to weeks) I would get a clutch squeal upon letting out the clutch. The sound was as like a squeal you would get from a sleeve bearing where both the bearing and journal were made from hard steel and no lubrication.
I took my new bike back to the dealer and let him know the problem and he said that a lot of the new bikes do this at first and to give it time and it should go away. I gave it a couple of weeks and it still squealed upon letting the clutch out. I took it back and the manager said he would try having his tech. install a cushion plate in the clutch like the GL1000 have. I got the bike back and it was a little better but still squealed off and on until I had ~4,000 mi on it. Leap forward 40 years when I restored my bike I got to rebuilding the clutch and remembered the squeal and saw that no cushion plate was in the clutch like the manager said he was going to do.
Although it is now 46 years ago, it still bugs me as to what the cause was and if it truly was a common occurrence with these bikes. Mark, can you shed any light on this? I figure if anyone knew of this problem it would be you. Anyone else that had a '76 750K (or any other year for that matter) that had this problem, please chime in!
-P.
Oh, yeah...for lack of a better description, I've called this noise the "clutch squak" sound when pulling away from a stop, especially with a cold engine.
It's actually not in the clutch - well, sorta in the area, though. It's in the cage bearing in the center of the clutch hub assembly, which Honda only sold as the assembly (and you split the cases to replace it!). The K6 bikes showed it early on after Honda had quit making the K5 for the F0 model (which sales fell flat for and then hurriedly started making the K6), sometimes with...umm...marginal parts (i.e., too-tight or too-loose tolerances: tight ones make noise when cold). They were the first ones to exhibit it right away: most of these problems appeared in the 'improved' clutch found in the post-1/72 builds of the K2, which remained the same until the F2/K7 bike. The 'improved' clutch hubs were simpler to make. The bearing is situated such that oil from the mainshaft trickles in to lube it, thru 2 half-round indents in the hub's casting. When the bikes sit for a long time, especially on the sidestand (like years) the oil drains fully away from the bearing, and if the old oil was wet it can cause rust or corrosion to partially block these passages, starving the bearing when the engine is cold. It gets a little more lube flow when the oil thins out with heat, usually making less noise in the process.
On my own K2 after I had cancer and didn't ride from 2001 to 2006, mine screamed bloody murder at every stop-to-takeoff letout of the clutch, A LOT, when cold. It was embarrassing (and with the Vetter, REAL loud!), so in 2008 I took the (engine and) clutch basket out and pulled the bearing, found another one in a used hub I had, and put it back together after scraping those 2 passages clean: they had some crud buildup in them and the long sit let it harden up.
I suspect that dealer had no idea what made the noise: few did. I only saw it because my shop was one of the very few "worst case repairs" kind of shop, where I got stuff that others failed to fix. (Basically, I think this was because I wasn't afraid to dismember the Mighty 750 like most shops?) The one bike I saw this on in those days had been started up and run about 4 miles with no oil in it: I guess the owner forget to refill the oil tank during an oil change (I think beer was involved...), or something like that. It galled this bearing (not to mention the crankshaft and rod bearings, and the crankshaft journals). Honda does not supply the bearing, although it is a common size (I have several of them somewhere), so I had to get a new hub to 'fix' it back then.
In more recent years I got a 750 from the Gulf area (USA) that actually had a high-water mark inside the engine from sitting for 30 years. It had slowly condensed moisture, drop-by-drop, into the crankcase by simply sitting with no oil changes or engine heat all that time. The water mark was halfway up the mainshaft. This bearing was real rusty: that was when I discovered that they can be replaced easily, and are common caged needle bearings. I'll have to dig thru my stuff, though, to find them and their size.
On yours: I might suggest, if you decide to dismember it, to closely measure the mainshaft site where this bearing rides (when you get there) and mic it to report it here. Being a needle bearing, the OD of the shaft at that site might be the offending item, if it is too large in diameter by as little as 0.01mm. In the meantime, while I have some engines apart, I'll go out and measure a few to see what this dimension is on a good shaft (I have about 6 trannies in boxes, too). If yours is too big, this can cause the noise because it is tightly packing the bearing's needle rollers between the clutch hub and the mainshaft. The hub (cast iron) and bearings (moly steel) will grow more with heat than the mainshaft (simple cast steel), usually making the noise go away after a good warmup. In the meantime, make sure your oil has ZDDP (zinc) in it, because this is precisely one of those spots in these engines that needs zinc, big time. Needle bearings need either zinc or long-chain synthetic oils (which these engines cannot ingest without other troubles) in order to run quietly and smoothly. If you're not running something like the Bel-Ray EXL Mineral oil (20w50), maybe get a gallon of it ($50!) and change the oil, then run it 500 miles or so to see if it helps to quiet it down when cold. If it does, stick with that oil for a while (forever would be good!) until the bearing and mainshaft can gain some clearance (like, 5k-10k miles? It is a slow-wearing part) which will then let it run quietly again. This bearing only gets used when the clutch is pulled in and the engine is in gear.
