buying 1981 CB750 C Exclusive

Posted: Sat Jan 16, 2021 12:20 am

I, dear members I'm Alex From Argentina, glad to found this forum, I'm next to buy a 1981 CB750 C Exclusive, it seems in very good condition, seller says never opened block and it seems all original, me and my father love these Customs, so its a very delayed dream, (me 52, Father 82)
I really would appreciatte any tip about what to look for, in inspection instance, later today will visit the dealer to inspect the bike, I have very good mechanics profile and some experience, but never put my hands on an engine like this (I had many XL 125, XR 600, actually a CM 200T Twinstar, and always had hands plenty of grease, I also restored completely a 1967 Mercedes 250 SE.

Really would like to know for example how to know if timming chain is worn, or if there are potential problems on valve train, I know this engine has 4 valves / cilinder, and hidraulic actuators.
Well, all info would be very appreciatted!!!, Saturday afternoon (local) is de D day!!
put some pics of the lady

Posted: Sat Jan 16, 2021 9:17 am

Welcome to the site Alex ... Smile

If you haven't read the following page , now is the time .
http://www.cb750c.com/modules.php?name=Forums&file=viewtopic&p=80601#80601

If you run into problems with any of that , Please let us know . Thanks . Smile

You might have a look at and download the Factory Service Manual , available in our Technical Documents section . It's free .

Sounds like you have a pretty good idea of what's good and bad in a bike .

Posted: Sat Jan 16, 2021 6:31 pm

Welcome here.

Nice looking bike!

How many miles?

Read the maintenance checklist linked in my sig.

Posted: Mon Jan 18, 2021 12:46 pm

Hi!, many thanks , very useful your tips list, thanks very much.
I believe it has 143.000Km, aprox. 90.000miles

Posted: Mon Jan 18, 2021 12:57 pm

On Saturday I went to inspect it,. very nice, very original and complette, except handlebar around seat.
a little smoke on left muflers, it apears reduced when engine warmed.
I made deposit, so hope not to be trgiacal.... it coul be said I´m the new owner!
when engine is hot it sounds really nice, bike was some time stopped.
brake disc are almos like new, dont belive the was changed. could it be 90.000miles and no significant wear?
thanks a lot

PS FSM, great!!!!!!

thanks a lot

Posted: Mon Jan 18, 2021 3:47 pm

Please fill in your location and sig.

Wow, 90K miles is quite a long life for one of these bikes without the motor ever being opened, quite rare IMO. If it still has good compression at that much mileage, I'd say it's had to have a lot of work beyond just good maintenance. They just don't last that long without some considerable engine work as a rule. Especially the cam chains and tensioners. Even changing oil every 1000 miles, my friends bike needed a complete overhaul at 100,000 miles.

So I couldn't hazard a guess at what your cam chains and tensioners look like. I've replaced them at 30K miles, but that was probably a bit early. The tensioner slippers can die from engine heat and crack and crumble when old. The chains die from lack of being adjusted properly, and a poor tensioner and guide design that allows them to whip back and forth at speed.

Maybe the mileage estimate is off. Could it actually be 43Km? It looks more like that. It looks too clean for 143Km miles. The forks and pipes usually have some pitting and discoloration just from dust, sand and dirt strikes while being ridden. Maybe it's just a real flattering picture.

Posted: Tue Jan 26, 2021 5:39 pm

Hi, many thanks for the comments,
yes probably it only has 43.000km, bike was stopped for a long time according owner comments, but there is a car dealer forwarding info... mmmm.
its no indicious of wear on front fork, exhaust is quite chromed, no yellow or rainbow coloration, engine bolts seems not be touched, except ex cam chain tensioner and clutch adjust. no noticeable wear on rubber rest for feet (sorry for the poor term to translate). will try to upload some pics.
the onlyu thing warning me is a little smoke on left cilinders, maybe stuck oil control rings... hope that...
I managed my signature content, pls tell me if its right
PS: tomorrow will go to bring it home!!!!

Posted: Tue Jan 26, 2021 6:01 pm

Congratulations on your purchase. It's a real nice looking bike!

Probably valve stem seals are hard and need changing causing the smoke. Head work is usually the first thing for these motors. If your compression is good, you should be OK for some time. Be sure to do all the maintenance on schedule. I recommend changing the oil at least every 2000 miles though. Use good quality motorcycle rated oil, not automotive oil. High priced synthetic oil isn't really necessary, these bikes contaminate the oil too quickly and need frequent changes, so the advantages of synth oil are few.

At 43Km you're cam chain tensioners are probably still OK. Cam chains generally last 80-100Km or maybe more if you keep them adjusted snug. Use the static method to adjust the cam chains, not dynamic. Cam chains do wear though, and the effect is that the cam timing changes and so power goes down. Adjusting can't fix it the cam timing though, it happens because the chains get longer from pin and hole wear in the links, not stretch, and adjusting only takes up the slack and reduces chain whipping.

Posted: Tue Jan 26, 2021 6:06 pm

HERE THE PICS.

Posted: Tue Jan 26, 2021 6:11 pm

MORE PICS

Posted: Tue Jan 26, 2021 6:13 pm

Please keep your inline posted pics under 640 pixels wide.

Posted: Tue Jan 26, 2021 6:13 pm

AND A FEW MORE PICS

Posted: Tue Jan 26, 2021 6:16 pm

AND 3 MORE

Posted: Tue Jan 26, 2021 6:24 pm

AlexRozzi2021 wrote:

HERE THE PICS.

Hi , many txs for your comments, I cinsidered valve stem seals, but its no noticeable more smoke after vacum due throttle cut, in my experience its seems like ring issue.
well, we will see...
what do you thinks about the real milleage after saw the pics?

thanks, again, Alex.

Posted: Tue Jan 26, 2021 6:35 pm

Please limit your inline posted pics to ~640 pixels wide.

Hard to tell from looking at pictures what the actual mileage is. Can't tell what's be replaced either, like footpegs and such.

Posted: Tue Jan 26, 2021 6:35 pm

Please limit your inline posted pics to ~640 pixels wide.

Hard to tell from looking at pictures what the actual mileage is. Can't tell what's been replaced either, like footpeg rubbers and such.

Posted: Fri Jan 29, 2021 1:06 am

OK, countdown finished, glad to tell that yesterday I bring my new 1981 CB 750 C exclusive, to her new Home!!!
a nice 70km trip , most on clear road, across the fields, with the hot summer wind in face, wow.... more than 15 years without riding a bike...

the bike runs great, finally very liuttle fumes on left cilinders, will se about evolution, no oil leaks, and all runs smooth, impressed with very elastic engine, next Week end, will check the entire bike, it needs carbs adjust, very poor idle, I also noticed a little hard suspension, need to check front fork air pressure, and rear springs preload and hidraulic control. (these rear shockks have a lever on bottom, I believe the adjust hidraulic damper). also need to check rear brake, (disc type) it has a long travel and very sponge effect

This bike has a very particular history, last night checking documentation I found that it wass purchased on 1982, 0km in Tokio, by a Argentine militar attachement at Yokohama, during his foreign service, and some years after that it was bringed , in 1988, to Argentina.

of course Im printing FSM, and beans Bike Maintenance Checklist wich will be invaluable help!

now have to thanks to all whom helped me with comments and suggestion, during this stage.

PS, this bike, in addition to being a desire of my own, it is my tribute to my father, who, since he first saw her, he love her, at first sight, next Saturday, me and my brother will take her, to share this gift, at his 82. Ik sure he will be very excited!!! and we will too.

will keep in touch, this , just starts!!!

Posted: Fri Jan 29, 2021 1:34 am

TAKEN PICS, WHEN BRINGING HOME

Posted: Fri Jan 29, 2021 1:37 am

Hi, any info about these mirrors?

Posted: Fri Jan 29, 2021 8:48 am

The bike seems in very nice condition . thumbs up

Maybe those are aftermarket mirrors ?
Below is a pic of the stock mirrors on the American 750C .

Posted: Sat Jan 30, 2021 8:39 pm

Sorry, no idea about those mirrors.

Posted: Sun Jan 31, 2021 12:34 am

Hi, yes, I´m sure my mirrors are aftermarket.
I found they have a red position light and yellow turn signl inside lens.

Posted: Sun Jan 31, 2021 12:39 am

AlexRozzi2021 wrote:

Hi, yes, I´m sure my mirrors are aftermarket.
I found they have a red position light and yellow turn signl inside lens.

Nice!