Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: Graeme77 on June 20, 2011, 09:15:03 PM
-
Whats the deal?
Mine rattles alot, quite loud!
Not used to bike engines, or chain driven cams etc so i adjusted the cam chain and checked the tappets to make sure neither of those were rattling (they werent).
Havent checked the primary chain yet but will do.
So, assuming all thats left is clutch rattle, how loud should it be?
Ive been told they all do, but is there any way to reduce it? I do have a spare new clutch. Why does the rattle not go when you pull the clutch lever?
I have heard brief mention about using a goldwing clutch plate to reduce rattle, but thats all the info i have. Anyone else shed any light on this?
-
FULL service then check the carb balance before condeming anything mate
-
As Bryan says, check the carb balance - but anything else you do will affect this so always do it last!
-
Mine does rattle somewhat as well and it does quieten done when I pull the clutch in, as the others have said check every thing and then balance the carbs.
Cheers
Den
-
All Hondas I've ever owned have had noisy engines but I think the important thing to determine is whether the noise gets suddenly worse. I know you do not have anything to compare it to but I suspect you need not worry unduly.
One aspect which I think is rather poor is that there is no way to adjust the primary chain and I imagine this is responsible for a lot of the noise. When I obtained my engine it had only done 7.5K and the primary chain was quite noisy, especially at tickover. However, it has not got any worse in years of riding. If your tickover is too slow it will be very pronounced.
-
Ill have a check and see how the primary chain adjuster is. Might pull the cam chain tensioner too, make sure its all working ok.
Its about as loud as the exhaust on tickover. Tick over at about 1200-1500rpm, but only had it running untill its just ok of choke, no longer really.
Engine has done 33000 but was rebuilt not too long ago. I have reciets for all the bits, including a cam chain i think.
I have a new chain in some spares but dont know if its cam or primary.
In a way, i'd quite like it to be the primary chain, would give me an excuse to pull the engine apart. I always at least take the head of any old vehicles i buy, just to have a look and see if all is well.
Thanks, ill report back if i have any questions or interesting updates.
-
They usually make more of a "rustle" sound if all in good order and much less clattering if that makes sense.
I've known a couple of these in the past that were thrashed beyond belief and they still sounded ok which suggests if you've got any major noise then it's possibly worth investigating if general set-up can't improve it.
They will sound noisier on choke if they are hunting around so need to be properly warmed to clearly judge but they never sound really smooth/whiney like a Kawasaki Z900 for example.
If you've got a lot of transmission backlash you'll be able to get some idea of it by rolling it back and forth in gear with the motor off, it shouldn't really travel that far (assume chain is adjusted well).
-
I played around some more this evening and it does sound like a chain.
I took the cam chain tensioner of and its fine. Not that far out when adjusted either so the cam chain should be fine.
Was looking at the carb air screws and the two cylinders which havent blued the exhausts (different subject i know) wernt set properly.
Ill get some gauges, or make some, to balance the carbs later.
Checked timing with a gun (electronic ignition) and its fine.
Im sure i can here a slight clutch rattle, and the main rattle. It does sound like a chain so next step i think is to remove the sump plate and measure the adjuster.
It doesnt like idling under 1000rpm so i think the carbs are deffo out of balance. If i hold it at around 1750rpm the main rattle goes but it doesnt go when just reved. Again, sounds like a chain to me.
Doesnt seem to be any backlash in the transmission. Ive been pushing it in gear to get it at the right point for setting the cam chain tension. The engine had stopped on 2/3, in 1st gear i pushed it to turn it over to 1/4 (no kickstarter). It was TDC on no.4 so pushed it forward more to get it up to no.1.
This only ended up with the bike maybe 1 foot further forward if that makes sense. Pushing the bike forward/backwards in gear to turn the engine has imediate effect.
The engine sounds very sweet, just with an extra added rattle :)
Ill probably pull the exhaust and check the primary chain tomorrow eve so ill let you know what i find.
Unfortunately i cant take it for a run to get it properly warm as i am still waiting for a date for my final test to get my full license :(
Trying to get the bike ready for when im legal.
-
Any reason why i cant use a sincle vacuum gauge to tune my carbs?
I have 2, an old snail type, and a 'ball in tube' type.
I used them to balance my cars (sidevalve ford on twin SU's and a zephyr 6 on triple SU's).
Sold the cars but still have the balancers.
Why do i need 4 gauges?
I know adjusting one carb effects the vacuum at the others, but its not too hard to do.
I have pod filters so can i run the bike without the filters and balance the carbs with the one vacuum gauge?
I assume the reason for the proper type of gauges using the proper carb connectors is so you can do this with the air box still attached?
I guess it will run well enough with no air filters to balance the carbs?
-
Believe me when i say after 30+ years of doing the job one gauge just dont cut it!
Yamaha used to supply one gauge with a rotary valve to select cylinders and that was a real pain in the A*se to use as well
-
Ok, :)
But im curious, why so bad?
Setting up triple carbs was more hassle than twin carbs, but still not too bad a job.
I can see why doing 4 would be more awkward, but apart from taking longer, i dont see any real problem.
Ive never done it though, and you obviously have. Many times no doubt, so i bow to your experience.
Just curious why so bad.
In one of my manuals it describes the build of some DIY fluid gauges, im sure you all know about these.
Looks simple enough. What i dont get though is why the need to make up carb plates rather than using fittings to link them up normaly. Are these type of gauges worth building rather than buying cheap gauges?
Cant really shell out for a decent set yet.
-
I've got a set of 4 (dial) gauges that go into the screw holes and as you adjust one carb the idle speed usually changes a bit so the vacuum reading for all of them shifts about so you have to chase them with the one you are working on if that makes sense.
You should eventually get there but may run round in circles as you approach ideal point as you can't see the others at the same time. That's all, I think.
-
Thats what i figured, will work, just more going back over them.
-
I have a load of Sensortechnic, millibar pressure sensors stashed somewhere, from a defunct 'Vapour recovery' work project. Anyone ever used four of these and a PC data logger to balance carbs. I assume you would have to damp out the signals to give a steady reading. Probably another project for days to come.
cheers ashD
-
Have done something similar for closed loop chemical flow, mag-drive in-pipe flow impelers reporting out to a PC. The software had to delay and damp the fluctuations to make the data useful, but we did end up with a useable reporting system. Probably much too complex for this task, would make a nice printout for a service shop to show customers though.
-
::) this post is getting interesting with all the jargon coming out ::) but" THE TRUTH IS OUT THERE " X-FILES,(bryan, K2 and spitfire) ,i can only do basic engineering ,so i will stick to my trusty 4 dial guages, timing light , and feeler guages :)
-
I agree.
I build hi fi amps and other hi fi electronics as a hoby, but computer based stuff is over my head LOL.
Ill use my single gauges this time (ill let you know how much of a pain it is!) then get some gauges later on.
-
By al means try it if you have loads of time JUST MAKE SURE that ALL the service items are done first
-
Steff750, the example I had was a chemical process that was basic but flow was critical for 6 seperate solutions and controlled by wopping great ball valves that everyone was scared to move in case we couldn't return it to original. We put in flow measuring impellers and sure enough the readout just jumped about all over the place (like a bunch of monkeys in a coffe house) making that report unuseable but then a clever computer guy at the company wrote a little program to collate and clean the data on a real time basis and it really worked. certainly opened my eyes as to the potential of mixing different mechanical, computer and pure maths logic systems.
It's engineers that have manufactured the modern world remember.
-
I'm trialling the Goldwing clutch plate mod. The plate is a heavy ol' piece of kit and basically takes up the space of one friction plate and one fibre plate. I'm still not sure how effective it is though, and I have a feeling the whole basket would benefit from stronger springs. I'll report back when I've been able to put some miles on the bike (see other posts for fun and games).
Meantime, this thread (http://forums.sohc4.net/index.php?topic=78643.0) might help give you some ideas for keeping the noise down a bit.
-
After going over everything, it seems the rattle is deffinately primary chain, and no doubt caused by the carbs being out of balance.
Tried using my single gauges, but the one i used to use is broken, and the other old one i found fluctuates wildly. As its the type you press onto the carb instead of the air filter, there is no damping it.
So, ill be buying some gauges then.
I see a few of you like the carbtune ones.
Ill look for them.
What are the cheap 4 gauge ones on ebay like? Cant argue with 40 quid LOL.