CB750A Hondamatic noise at startup

Erik

Hello, I'm new to this forum so I hope I don't violate any rules.
I have a '75 CB750A which I bought in parts. With the help of a friend we assembled the engine and installed everything back together but since then when I start up the engine there is a metallic noise on the torque converter side which disappears when the engine gets warm. I have replaced the torque converter to no avail.
After that I have pondered various possible causes, the one that keeps coming back is the fact that there are apparently three oil 'check valves' in the oiling system which we failed to check their presence during assembly. However, I would love to get some sort of confirmation before taking apart the whole engine again. Are these check valves (or small orifices) present to avoid oil starvation during start up?
If anyone can give some more information on this subject your help would be much appreciated.
Thanks,
Erik

zjeppe · Posted: Sun Jun 05, 2011 12:05 am Post subject:

Erik, ik heb wel ne four zevenenhalf in de collectie, maar ken niks van die automaten Embarassed

D'er zijn er hier wel, dus, wacht maar af Wink

05c50 · Posted: Sun Jun 05, 2011 6:37 am Post subject:

Hi Erik, we might need a little more information about your noise. Does the noise seem to change with engine speed.......does it go away when you increase the idle? "a metallic noise".......tick,knock,rap,clunkety-clunk?? The 4 cylinder Hondas from that era can have a pretty loud primary rattle if the carbs are not syncd properly. The check valves that you mentioned are used mostly to control oil circulation to the head and valve train. If they become clogged (a common problem if too much gasket sealer is used during engine assembly) they will cause extreme damage to the camshaft and rockers. That noise will be loudest at the top of the engine. If the engine has high mileage, the noise may be a combination of a stretched primary chain and out of sync carbs. It can be quite loud and very alarming if you haven't heard it before. This noise will usually quiet some when the engine is warmed up and idlyling correctly. Hope this helps.

.....................Paul

zjeppe · Posted: Sun Jun 05, 2011 8:47 am Post subject:

Do not know much about the auto, but, as the loud noise from the douible primary chain for the "normal " fours (750's) I 'm pretty shure the automatic had an " Hyvo chain"(Of course, thyat can make noise to, but it was done to avoid that Idea

)

Erik · Posted: Sun Jun 05, 2011 12:25 pm Post subject: CB750A Hondamatic noise

The noise, to my ears a rattling noise, as in too much play from mechanical parts, does not come from the top of the engine, but from the lower RH side. I think we can rule out the primary chain, because my friend advised replacing it with a new part, in view of his experience with ordinary CB750's. The noise disappears when you increase the rpm's and also when the engine gets warmed up.
The remark about the oil jets for top end lubrication confirms what I suspected so I presume we can rule that out to.
Maybe I should check parts differences a little bit more, perhaps torque converter or axles were changed, because I suspect Honda did change the '76 and '78 models compard to the '75 and I have mixed up parts.
To Paul: had a GL1000 previously, will attach photo.
Thanks for all the input, all contributions are very welcome and much appreciated.
Erik

Erik · Posted: Sun Jun 05, 2011 12:37 pm Post subject:

OK so maybe my previous message was a bit lacking in information.
The noise only happens when I start the bike with a cold engine.
When I rev it with the cold engine it disappears. When it is warming up and the idle speed goes down the noise comes back until the engine is fully warmed up, then it doesn't manifest itself anymore. I then can drive the bike without any noise. This leads me to think it must have something to do with lack of oil.
Just for the fun of it, another picture of the same GL1000 with different color and seat (still miss that bike but it was soooo heavy).

05c50 · Posted: Sun Jun 05, 2011 8:06 pm Post subject:

Very nice wing Erik. Here in the states, the Solar Yellow 76 is becoming somewhat of a cult bike. Although they weren't very popular when new, many people are restoring them, or looking for them.

My 750A has noise when started and goes away when warmed up. It's never been something that I was concerned with, because all the others that I've heard had the same noise.

...............Paul

Erik · Posted: Mon Jun 06, 2011 4:16 am Post subject:

Now that could be a possibility too, I recall having read some sort of comparable remark, that they all make noise when starting up. So all other Hondamatics you have encountered had the same noise? I cannot imagine that Honda would have accepted this as being normal.

05c50 · Posted: Mon Jun 06, 2011 7:50 pm Post subject:

I don't think we could call the noise a normal noise, more of an "inherent condition of that model". Many of the Honda sohc/4 engines have an inherent noise after a few years of use. Many have the rattle,rattle,clunk,clunk until the clutch handle is pulled in, but since the 'matic has no clutch, we just have the clunkety,clunkety, clunk until it's warmed up.

...............Paul

Erik · Posted: Tue Jun 07, 2011 1:08 pm Post subject:

I have been in after sales for most of my working life, and you sound just like a service manager explaining to a customer why the incredible ratchet his new machine is making is totally normal and that there is not even the slightest remote possibilty that anyone could have a look for, heaven forbids, a repair under warranty Laughing

But hey, cool, my machine has the standard rattle,rattle,clunk,clunk,clunkety,clunkety,clunk that all Hondamatics have Very Happy

Don't get me wrong, I'm absolutely not sarcastic and I really laughed with your last post. Thanks for the great feedback and, for the moment, unless someone else proves us wrong I'll assume that I don't have to worry about the noise. If I ever get in your neighbourhood I'd love to hear the sound your Hondamatic makes. Do you have any pictures of it?

Regards,

Erik

05c50 · Posted: Tue Jun 07, 2011 7:03 pm Post subject:

Hahaha, guilty as charged. I've been an automotive service manager for the last 35 years. I've always worked in "after sales" (European for service department). You have to be careful using the word "normal". Smile

Some noises are an indication of a serious problem, and some are something you have to live with......an example.........mother in laws whining. Laughing

Stu, aka bikegeezer also has a 'matic, but I guess he's been busy because he hasn't chimed in yet.

I've got some pictures somewhere and I'll post them here.

............Paul

Erik · Posted: Wed Jun 08, 2011 1:31 pm Post subject:

Very nice, much shinier than mine!
Had an idea yesterday, next time I start it up I'll try to make a short video (is it possible to post here?) so you can hear the noise. Unfortunately I'll be busy for work the next few days but I'll keep you posted.

Erik

Honda CB750A 1976
Suzuki CS50 1984
Suzuki GR650 1983

05c50 · Posted: Wed Jun 08, 2011 3:30 pm Post subject:

I don't know if you can post a video here, but you could put it on you tube and link it.

.........Paul

Bikegeezer · Posted: Wed Jun 08, 2011 5:42 pm Post subject:

Okay, I'll chime in, for what it's worth. But I'm sure not a 750A expert. The rattle is the primary chain. When my bike is cold, the thick oil puts enough drag on the driveline, even in neutral, to keep the chain tensioned and quiet. After the bike is warmed up, it'll rattle like hell in neutral. But if it's in gear, it's dead quiet. I get around the rattle by shutting the bike off in gear when I'm done riding. Maybe I'll get a better synch on the carbs. That should help a bit.

Stu

Erik · Posted: Sun Jun 12, 2011 7:11 am Post subject:

I tried to capoture the noise as best as I could and posted it on YouTube:

http://www.youtube.com/watch?v=bHgiUr1kOqc

It's not that clear but I hope you could confirm that this is indeed a normal primary chain noise.
Thanks for going through the trouble to watch it and give your comments.

Erik