Author Topic: Well, the bike didn't make it to the mechanic today. PROBLEM FOUND 5/25 (Read 4247 times)

Dolomite · « **on:** May 14, 2020, 08:41:03 AM »

Decided to bring the bike to the mechanic to try to sort out this smoking issue as it was so bad my collector was leaking oil like it was a jelly donut. Was idling high but figured I could make the 20 minute trip as it seemed fine above 2k rpm. Boy was I wrong writing this now as I sit on the sidewalk at an intersection waiting for the mechanic and his trailer.

Sudden loss of power on the highway, looked like I was crop dusting in the rear view mirror. Managed to get off the highway and cut out at an intersection. Oil bag smoking, oil coming out the jug mids, the rpm cable, the breather cover, the head.

Well at least it's a nice day.

69cb750 · « **Reply #1 on:** May 14, 2020, 09:28:38 AM »

Quote

looked like I was crop dusting in the rear view mirror

Do you have a crop dusting license ?
Could be hole in piston of breather tube plugged.

Kevin D · « **Reply #2 on:** May 14, 2020, 11:51:11 AM »

Sorry for your troubles Dolomite. It's no fun when your CB isn't purring like it should.

ekpent · « **Reply #3 on:** May 14, 2020, 05:05:34 PM »

I'll never forget my much anticipated inaugural ride on my newly assembled Russ Collins 836 goodies. I was excited to try it and it was smoking. Thought it would be clearing up after bedding in. WELL it left an embarrassing cloud of smoke and I had to ride in the back of the pack. Finally fouled a plug after 30 miles. Got her home and found out that I had put the oil scraper rings in upside down.Always fun pulling the engine out and apart again after 50 miles of ride time. Ah yes the early days

I will say it ran like a charm and no smoke the second time around !!
Hopefully you get it worked out and have a nice solid bike you can trust to take you to new adventures.

grcamna2 · « **Reply #4 on:** May 14, 2020, 07:16:32 PM »

Your CB750's were smoking like Kawasaki H2 750 2-strokes ??

Dolomite · « **Reply #5 on:** May 14, 2020, 09:02:10 PM »

Quote from: grcamna2 on May 14, 2020, 07:16:32 PM

Your CB750's were smoking like Kawasaki H2 750 2-strokes ??

It was smoking like a whore in church...... who was also set on fire

Stev-o · « **Reply #6 on:** May 15, 2020, 08:53:05 AM »

Quote from: grcamna2 on May 14, 2020, 07:16:32 PM

Your CB750's were smoking like Kawasaki H2 750 2-strokes ??

Hey! I resemble that remark!

Dolomite · « **Reply #7 on:** May 20, 2020, 08:31:04 PM »

Mechanic finally got a chance to start on the bike today (he had a full workload for the week as it wasn't expected that my bike would be left there, was just supposed to be an afternoon thing). Exact message I received from him, minus any personal info.

"I did some test and the compression is low. I ordered a endoscope so I can look down in the cylinders. At least one spark plug had a lot of aluminum spray . That is usually from running lean. I hope to more and try to figure out the cause."

scottly · « **Reply #8 on:** May 20, 2020, 09:18:16 PM »

What ignition system are you using?

Dolomite · « **Reply #9 on:** May 20, 2020, 09:21:52 PM »

DynaS

scottly · « **Reply #10 on:** May 20, 2020, 09:27:22 PM »

Thanks. The Dyna S is probably not an issue in this case.

bryanj · « **Reply #11 on:** May 20, 2020, 11:26:36 PM »

Sounds like melted piston(s) to me

Dolomite · « **Reply #12 on:** May 21, 2020, 09:36:27 AM »

My suspicion still leads me back to rings. Whether one failed or there was issue with installation, it would explain why the bike started fine and progressively got worse (as the ring wore out more), the low compression and the oil in the exhaust/ smoking exhaust.

Dolomite · « **Reply #13 on:** May 25, 2020, 11:36:50 AM »

Quote from: bryanj on May 20, 2020, 11:26:36 PM

Sounds like melted piston(s) to me

Someone give this man a prize.

Mechanic called today and asked me to come down when I had some time. Went down and he showed me some aluminized plugs, and on the fiberoptic camera the number 1 piston that had melted so much, it let the oil run out of every orifice.

I don't know what to do at this point, we have a rough plan, but I'm looking at around $1k, and that's IF the cylinders can just get rehoned. If the walls are toast. Then we need to decide if its better to bore and sleeve, or go up from the 836. This will put me $5k into a bike that I could sell for maybe $2500.

scottly · « **Reply #14 on:** May 25, 2020, 01:20:36 PM »

How many of the plugs were aluminized?
Per your PM, here are the instructions for cutting the frame to install a frame kit:

Dolomite · « **Reply #15 on:** May 25, 2020, 01:28:37 PM »

Plugs 1 and 2 definitely, little on 3, 4 was oily.

754 · « **Reply #16 on:** May 25, 2020, 05:53:46 PM »

You can fix it quite cheap, but you need some time to find a used barrel and piston.
At that point you can get away with 1st over, at less cost than a 836 kit . Somtimes you can just change a sleeve and a piston.

But the question remains what caused the melted piston.? If it was ignition it would be two pistols I would think. Maybe plugged main jet ?

scottly · « **Reply #17 on:** May 25, 2020, 06:02:41 PM »

There is evidence of melting on three plugs, and the 4th has been oily since the trouble first started??

Dolomite · « **Reply #18 on:** May 25, 2020, 09:46:50 PM »

Yes, to the plugs. And engine is already bored to 836, so if the cylinders can't just be honed, the question is which is easier/ cost effective: resleeve the 836 or bore over to 890?

scottly · « **Reply #19 on:** May 25, 2020, 10:32:40 PM »

Wait until the autopsy is done before making any decisions..

Dolomite · « **Reply #20 on:** May 25, 2020, 10:38:07 PM »

Naturally, just trying to find all my ducks and line them up.

scottly · « **Reply #21 on:** May 25, 2020, 10:42:51 PM »

The biggest bore for stock sleeves is 850, IIRC. The big question is why the melt-down?

Dolomite · « **Reply #22 on:** May 25, 2020, 10:52:44 PM »

Something caused it to run super lean for an extended time and we can't figure out what.

When it was originally setup with a modified box it was running 127.5 jets. That box failed so I changed to stacks. Would running stacks with a 127.5 main cause a lean enough condition to melt pistons? Also the pistons may have been a poor cast, they were in plain white boxes when they arrived, won't mention where they were purchased from. It's running a dynaS ignition with 5ohm coils, 7mm copper core wire; was running normal ngkd8ea plugs, changed to densos in the last 300mi or while chasing the smoking issue, Cx1 cam with no headwork. Was originally running mack 2-1s, changed to a delkevic 4-1 for the past 100 miles or so. Any insight on where to look other than if the carbs just #$%* for some reason and weren't pumping out a good mixture?

bryanj · « **Reply #23 on:** May 25, 2020, 10:58:02 PM »

Could also be timing too far advanced

rotortiller · « **Reply #24 on:** May 26, 2020, 04:18:54 AM »

Running stacks without an air filter is a sure way for dirt to abrade the inside of the engine. It sucks for sure having all that damage.

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Author Topic: Well, the bike didn't make it to the mechanic today. PROBLEM FOUND 5/25 (Read 4247 times)