1981 Honda CB900C engine issues

after leak down test, possibly bad exhaust valves, and piston rings
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[@danmorrissette4814]

Valve shims adjustment and cam chain tension was key in those engine to run smoothly.. i had 3 of those !

[@thedragon2299]

Compression is also the key to them running smoothly, which this one didn't have. I have had to rebuild alot of these engines over the years. Here's one I did that had burnt valves at only 6,600 miles kzbin.info/www/bejne/e4KygaSinN2JeLs

[@grabir01]

If it has been sitting a long time. Years.. It will show low compression. Put some pre mix into the jugs. Run it. After a few heat cycles, the rings will start to seal again and compression will go up. I bought a 1979 gold wing that had not run for over 30 years. 114 112 110 118 psi. Pulled and cleaned the carbs, trickled in some pre mix and lit that sucker!! After running and being a fogger for the first 5-10 mins and then it cleaned up. Compression is is up over 155 now. I have put a few thousand miles on it. It is a standard and a hoot to ride. Fast and fun. I am guessing 80 hp or so. I have not cheked my belts yet.. Yikes!! Also.. PSI will be higher cold typically. On a motor that is in service anyway. If it has been sitting for years, no telling what compression will be except super low. Anything over 90 a motor will run.

[@thedragon2299]

No it hasn't been sitting along time. It appears that once upon a time the carbs were flooding the cylinder with gas, and the owner didn't realize it until it was too late. The rings and cylinders are worn. Customer brought it to me, because he thought the carbs needed adjusted. I appreciate your advice, as far as bringing bikes and cars with stuck rings back to life, you are talking to the King here, been doing it for over 30 years, have done hundreds. You can start to binge watch by videos and see how many I do. It's 90% of my business. Thanks for watching and commenting 🐲

[@grabir01]

@@thedragon2299 I have been doing it for over 50 years. And have built thousands of engines. That Honda must have well over 100-200k miles to have the rings and jugs worn so badly. Check and see what valve clearance you have, Could be some of them are floating.

[@michaelcschmitt]

Beautiful bike

[@thedragon2299]

Indeed it was! I did another one before that one, that was in slightly better shape than this one, check it out here: kzbin.info/aero/PLICWLX3xQIRNjFNcHhBGr1XAL1u5WY7-H&feature=shared Thanks for watching 🐲

[@buzzfgo]

I have an 81. 150 PSI in each cylinder. Runs very strong. The only issue I can't seem to get a grip on is from idle and take off. It bogs but then quickly picks up. Also noticed when coming to a stop, my revs are high... like it's stuck, around 4k rpm. If I have the bike in 1st and pop the clutch the rpm goes back down to normal. Slide on a carb?

[@thedragon2299]

RPM hanging up sounds like vacuum or intake leak. Bog on take off is usually rectified by raising the slide needle a bit, but first fix you other problem and the bog might go away.

[@thedragon2299]

You can spray carb cleaner around intake boots to see if rpms raise to find leak, If you don't find a vacuum or intake leak, next cause of your condition is lean from lack of fuel caused by either dirty pilot jet or circuit, too small pilot jet, or simply raise your slide needles one step until it goes away. Hope this helps.

[@ScottMiller-tu3gg]

I have not dove into mine yet, but 3 of my cylinders read really low compression and after watching this, I feel I might have the same problem. Have you run into this problem with Suzuki / Kawasaki / Yamaha bikes much?

[@thedragon2299]

Sorry I didn't see this comment until now. Did you ever tear into yours?

[@ScottMiller-tu3gg]

No@@thedragon2299

[@BibTheBoulderTheOriginalOne]

Hi. I am on the verge of buying a 1981 CB900C here in the UK. It is an American import with 20,000 miles on the clock. Is the cost of rectifying these issues extreme? Love the bike, love its shape, but don't want to buy a bike that will empty my wallet "when" not "if" it has these problems...

[@thedragon2299]

I want to apologize to you, I never saw a notification for this comment and missed it some how until just now. Did you end up getting the bike?

[@BibTheBoulderTheOriginalOne]

Thanks for the reply. I ended up giving it a miss due to what I read about its unreliability. I have since bought a ZZR1400 and a Honda NC750X. Also considering a Triumph Rocket iii (2006)@@thedragon2299

[@JoseyWhales-ii4dk]

Dang looks show room condition...🤔 how many miles is on those rings?

[@thedragon2299]

Think it had 26,000 miles on it. If you think this one is nice, you should see the one I did a year before this one:kzbin.info/aero/PLICWLX3xQIRNjFNcHhBGr1XAL1u5WY7-H&feature=shared

[@thedragon2299]

Here is my Dragon Worx Facebook page too:facebook.com/profile.php?id=100057489818717&mibextid=ZbWKwL

[@JaymarDelaCruz-ck6nc]

🎉

[@petev.9357]

How many miles on the bike. First I heard about notorious for exhaust valves. With those test results I'd figure it's at 80k miles.

[@thedragon2299]

26,000 miles. They are certainly known for burning valves. Usually due to idling too long in hot weather, seems to be the cause. I just had one a couple months ago that had 6,000 miles on it with burn valves. Thanks for watching 🐲

[@thedragon2299]

kzbin.info/www/bejne/n6fZoHaZiLOjb68

[@petev.9357]

How are the 91-03 750 Nighthawks with valve or ring problems or any problems that you know of? 26k is very low to me for those problems. Did the exhaust valves burn due to too tight valve clearance?

[@thedragon2299]

@@petev.9357 to be honest they don't come in the shop often, so they must not have many known issues, so they must be pretty reliable. I have heard talk of 2nd gear issues in some, and the stator issues have always seem to be a topic with nighthawk, but mostly the older ones. The Nighthawks are some of my all time favorite bikes. I bought and sold so many 650's back in the day, such a fun peppy bike to ride.

[@thedragon2299]

@@petev.9357 to answer second part of your question, it appears that the ones that had burnt valves were due to long idle time in hot weather. So really the bike isn't notorious for burnt valves, so much as they are vulnerable to it if the user let's them idle long periods or over heats them in any manner.

[@dp97303]

that old id have the engine taken down to pieces and rebuilt all the way up all new parts piece by piece and electric as well then being a Honda it would run forever Honda bikes are reliable

[@maiktajda]

Hi I know that this video is for a year ago, but i have to try to find some parts for my cb900c, Do you have him repaired or not!? Maybe you have some parts. I am living in Nederland 😂😂 but dosen't matter if i can find some nice parts. Thanks and regards Mike

[@thedragon2299]

Sorry, don't have any parts.