Exhaust Valve Issue Concern -- 1979 CBX

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Exhaust Valve Issue Concern -- 1979 CBX

Postby mjfields_228 » Mon May 06, 2019 9:52 pm

There are so many things this issue might be that I am seeking input on so lets start with the basics.

1979 CBX1000 with a totally rebuilt motor (TIMS CBX) with about 3000 miles on since refreshed.

Airbox Delete running K & N Pod Filters.

OEM Carbs recently redone by Old School Carbs

Bike has been running fantastically the last several month. Fires right up after sitting for a week or more.

I recently perform the cam chain tensioner tighten procedure called out in the OEM Manual. This quieted lots of the rattle down.

Life is good in CBX Land--until this evening. I picked up the CBX out of my storage unit where it has been parked about 7 or 8 days on the battery tender at about 4:30 and rode it up the street to get gas then back home. Parked the bike on its side stand (with the Petcock off) and waited out a nasty Florida rain gusher. 6:01PM, I head out to my patio where the CBX was parked to take my evening therapy ride. Throw my leg over and completely upright the bike, turn on the Petcock, turn the key on and pump the throttle twice, press the starter and I get a god awful sound like the starter slipped a couple gears or some other mechanism protesting and the bike struggles to turn over. Mortified that I just experienced perhaps the dreaded Hydrolock I have heard about around the camp fire late at night I let off the starter button for a few seconds, turn off the key. Took a deep breath and turn the key back on and pressed the starter button again. This time the bike turned over albeit labored and started. But immediately I could tell something was not right. Total pitch change coming out of the exhaust, poor throttle response, and just rough running. Thinking I just needed to work out the cramp--so to speak--I rode out to my parking lot and did a 360 walk around and could see no signs of oil leaks or anything obvious. So what would Burt Munro??? Ride the thing around the block to see if things clear up or get worse. Bike runs terrible at about 65% power. I felt all 6 headers to see if I lost a coil and all six were toasty hot. How the bike is running and sounding to me it feels like I lost an exhaust valve somewhere in the system.

That god awful sound that I wrote about above came from the top of the motor on the left hand side.

Well being unable to channel Burt Munro anymore this evening I am not sure where I should start first..... Compression test starting left to right? Carb inspections?

Trying to remain positive and optimistic here but this CBX project has been a cluster since the day I picked up the bike in Dec 2016.
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Re: Exhaust Valve Issue Concern -- 1979 CBX

Postby Rick Pope » Mon May 06, 2019 10:31 pm

Quick check.... pull your #1 and #6 plugs, and verify they qre the sme distance from the seat of the spark plug. Let's hope they are.
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Re: Exhaust Valve Issue Concern -- 1979 CBX

Postby daves79x » Tue May 07, 2019 6:45 am

Rick's advice is a good place to start. Hydro-lock can happen to any cylinder, most commonly #1. Do you hear a rapping sound now from the engine that wasn't there before? Usually a good indicator as well. See how those checks go and report back.

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Re: Exhaust Valve Issue Concern -- 1979 CBX

Postby mjfields_228 » Tue May 07, 2019 8:06 am

After I get home from work today I will check the #1 and #6 plugs--thanks for the quick response. And as to a new rapping sound since this all manifested? I do not want to lead the witness but, yes, the normal symphony of valves clicking and clacking along with the cam chain noise is now joined by a new distinctive knocking sound. Apples and oranges with this comparison but I was once on a cross country trip on my 2012 BMW R1200GSA and the bike experienced a exhaust valve spring fracture. But the change is exhaust sound pitch, loss of power and a distinct knocking sound is eerily similar. Again, not trying to lead the witness!!

More on this subject later.............................
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Re: Exhaust Valve Issue Concern -- 1979 CBX

Postby mjfields_228 » Tue May 07, 2019 8:19 pm

Todays minimal investigation revealed nothing new. I pulled the #1 and #6 plugs, inspected them and took multiple measurements using a digital caliper. Everything looks okay.

I put the plugs back in and started the bike (this time no helmet on my fat head and I was kneeled down right next to the massive engine. That knocking sound I heard yesterday is actually the clutch basket making noise. I had the "upgraded' clutch mod as part of my TIMS CBX rebuild and never would think the new one would make such a fuss.

Without burning my face I put my good ear right close to the exhaust cam (both sides of the bike) and the best I can tell everything under cover sounds good. So I am back to one possible scenario of dropping a coil perhaps--either intermittently or just gone bad and it is resulting in the lack luster motor performance. I don't want to whine but I have chronic back pain from a bad get off in 2015 and I was not up to tearing into the bike any further today. I'll tackle it when I am feeling better.

I am hopefully not suffering from denial--but this may not be as serious as I originally considered!!
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Re: Exhaust Valve Issue Concern -- 1979 CBX

Postby swarrans » Wed May 08, 2019 2:27 am

Fingers and toes crossed for you!

One of the reasons I sometimes think about moving my beautiful CBX along to someone younger and less pessimistic is that I'm literally terrified of it going wrong!

However, when you're crusing along and those 6 cylinders are purring beneath you all the worry seems worth it!

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Re: Exhaust Valve Issue Concern -- 1979 CBX

Postby Larry Zimmer » Thu May 09, 2019 11:28 am

"However, when you're crusing along and those 6 cylinders are purring beneath you all the worry seems worth it!"

Got that right, Simon. It's what keeps me and my 82 going.
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Re: Exhaust Valve Issue Concern -- 1979 CBX

Postby mjfields_228 » Tue May 14, 2019 12:01 pm

Call me Chicken-Little or similar--because the CBX is running like a top again! The more and more that I think about it now right before the bike acted up last week there was a Florida gusher rain storm for about 30 minutes and the bike got adequately soaked while parked. Either I had some water intrusion onto one of the coils or a love bug plugged up the main jet of carb #2, whatever, the bike has self heeled and I enjoyed a delightful 2 1/2 hour ride on Saturday.

Still not sure if I would it from Florida to California and back but I will certainly enjoy it a whole lot running around locally!
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Re: Exhaust Valve Issue Concern -- 1979 CBX

Postby Larry Zimmer » Tue May 14, 2019 9:05 pm

Fingers crossed this is an "all's well that ends well"! :-)
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