CB750 K0/K1 Hybrid

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cfairweather
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Re: CB750 K0/K1 Hybrid

#346

Post by cfairweather »

You could be right about the crank, but the most likely scenario is the top end lost oil pressure due to the tiny orifices' becoming plugged.
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ritalz
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Re: CB750 K0/K1 Hybrid

#347

Post by ritalz »

Well that sucks. I know it's a crap shoot when working with old motors but I would be bummed out also.
Al

2003 Goldwing Daily Rider
1975 Goldwing 'Max'
1984 Goldwing New Bagger Project
1976 Goldwing 'Grocery Getter' Sold
1985 Goldwing Interstate 'NCC-1985' sold
1981 Silverwing Sold
1982 Goldeing Project Sold
1981 Goldwing Parted Out
1983 Goldwing Project Sold
1973 CB500F Long Gone
1966 CL77 First Street Bike
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Shadowjack
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Re: CB750 K0/K1 Hybrid

#348

Post by Shadowjack »

Doesn't take much restriction to wipe a cam lobe or two.
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Lucien Harpress
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Re: CB750 K0/K1 Hybrid

#349

Post by Lucien Harpress »

Yeah, I'm curious. The APE studs didn't leave much room around the oil feeds, and I won't rule out the o-rings I used being a hair too big. The only reason I was leaning toward crank bearings was that was the biggest change I made to an already well-running motor.

Eh. Either way, I'll pull it apart once I line up a replacement. Gotta add some parts to the Wall Of Shame, I suppose.
Last edited by Lucien Harpress on Thu Jun 01, 2023 9:01 am, edited 1 time in total.
1997 Valkyrie- Light Cutomization, but Too Busy Riding
1980 KZ1300- Bike's Haunted
1976 GL1000 (Yellow)- It Runs (Poorly) and Doesn't Leak (Mostly)
1974 Velosolex 3800- Better Than Walking
1972 CB750- Broke the Chain And Ate the Motor
1969 CT90- The Most Fun You Can Have on 90ccs.
1965 CA77 Dream- Needs a Full Teardown, but Complete

All advice I give is only valid until an expert corrects me.
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CYBORG
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Re: CB750 K0/K1 Hybrid

#350

Post by CYBORG »

not the wall of shame, the "the wall of learning experiences" :lol: :lol:
1978 custom GL1000
1977 custom with 1200 engine
1985 gl1200
cfairweather
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Re: CB750 K0/K1 Hybrid

#351

Post by cfairweather »

The APE studs aren't the problem. Oil will go around them with no problem. If the engine was not absolutely clean inside, this will happen. Don't feel too bad because this happens to expert builders too. I suspect the oil tank had some residue in it or some of the original black sealant plugged the orifices. If so, you will only need to remove the head and get everything perfectly cleaned out. Clean the oil pump, passages, oil tank, etc. Remove the orifices and run a wire through each hole. After you get it back together, rig up a way to turn the oil pump gear and pump oil through the engine so you can verify it works. You might see it work and then it stops pumping due to more crap plugging it again. Try using a vacuum cleaner to help get the passages clean. You will need a new camshaft, but the bottom end will probably be fine. Consider a CX1 cam from Cycle-X. You will be able to quickly determine if the top end is gone by inserting an inspection camera into a tappet cover hole. One question: Did you have the hose from the top tappet cover connected to anything or was it venting to fresh air?
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Lucien Harpress
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Re: CB750 K0/K1 Hybrid

#352

Post by Lucien Harpress »

To answer your question, the vent on top of the valve cover was vented directly to atmosphere. I ran the end of the hose down to the drive chain, the same way it was ran when I brought it home (and figured it was a mostly K2). For the record, I ran the larger vent hose from the oil tank to the same location.

I went ahead and drained the oil today. I'm trying to drain the filter as much as I can to check for debris, but initial impressions don't show a lot of shiny metal, if at all. There's quite a bit of grey stuff on the inside of the filter housing, which I would guess would have the consistency of dust if it weren't mixed with the oil. It definitely feels like aluminum dust. I plan on running the oil through a coffee filter or two, just to see what kind of shmutz I can pull out of it, if any.

I also pulled the valve adjuster caps from the intake and exhaust of cylinders 1 and 4. There's AN amount of oil on both, but the bike has also been sitting for a couple days. Not to mention I have no point of reference to what an "acceptable" amount of oil would be.

Just for fun I pulled the spark plugs and tried spinning it over with the kickstarter. The motor still turns, but there is still a tight spot where, if the engine stops in that position, I've got to put quite a bit more effort into breaking it loose. This is something that existed ever since I got the bottom end put back together, even before the top end went on. That said, I'm not ruling out top end starvation either.

My dad's got a scope camera, so I plan on taking a peek around at what I can this weekend. Hopefully I can see something.
1997 Valkyrie- Light Cutomization, but Too Busy Riding
1980 KZ1300- Bike's Haunted
1976 GL1000 (Yellow)- It Runs (Poorly) and Doesn't Leak (Mostly)
1974 Velosolex 3800- Better Than Walking
1972 CB750- Broke the Chain And Ate the Motor
1969 CT90- The Most Fun You Can Have on 90ccs.
1965 CA77 Dream- Needs a Full Teardown, but Complete

All advice I give is only valid until an expert corrects me.
Shadowjack
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Re: CB750 K0/K1 Hybrid

#353

Post by Shadowjack »

You knew there was a tight spot before you started it?
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Lucien Harpress
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Re: CB750 K0/K1 Hybrid

#354

Post by Lucien Harpress »

I had my suspicions, but I kept going with it for a couple reasons. First, I've never messed with bottom ends before, so I have no frame of reference to what "too tight" would be. When it was just the crank in the bottom end I could always spin it by hand, there were just spots that had a bit more resistance than the rest. Secondly, if I did have the wrong size crank shells installed, I don't have any way of actually knowing how to fix it. I don't have the tools to measure it.

Plan B was always a replacement bottom end. If what I built worked, great. If not, I spend a couple hundred bucks for a replacement, I re-use what I can from my top end, and learn what an incorrectly built engine feels like.

This is like the third time I've had a 750 engine in or out on this bike by now. I'm getting pretty good at it. :lol:
1997 Valkyrie- Light Cutomization, but Too Busy Riding
1980 KZ1300- Bike's Haunted
1976 GL1000 (Yellow)- It Runs (Poorly) and Doesn't Leak (Mostly)
1974 Velosolex 3800- Better Than Walking
1972 CB750- Broke the Chain And Ate the Motor
1969 CT90- The Most Fun You Can Have on 90ccs.
1965 CA77 Dream- Needs a Full Teardown, but Complete

All advice I give is only valid until an expert corrects me.
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Rednaxs60
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Re: CB750 K0/K1 Hybrid

#355

Post by Rednaxs60 »

Had to use bearing scrapers to install steam turbine and other equipment bearings (slightly larger than a 1200 crank bearing) when I was in our Navy. The bearings would come with new babbit, we would plastigauge, then use metal bluing to determine high points, scrape the bearing until the bluing was just right, plastigauge again, then secure.

You could do the same thing. Use metal bluing to determine which bearing is slightly out of round. Scrape the bearing ever so gently, or use sand paper to remove high point(s), plastigauge, then secure.

Good luck.
"When writing the Story of your life, don't let anyone else hold the pen."

Ernest

1985 GL1200 Limited Edition
2014 Can-Am Spyder RT LE
2021 Royal Enfield Himalayan
1995 GL1500 SE CDN Edition (sold)
2012 Suzuki DL1000 VStrom (sold)
Ontario 1985 GL1200 Limited Edition (sold)
2008 GL1800 (sold)
Shadowjack
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Re: CB750 K0/K1 Hybrid

#356

Post by Shadowjack »

If it only gets tight in one spot, it's either a main journal out of round, or a bent crank.
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Lucien Harpress
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Re: CB750 K0/K1 Hybrid

#357

Post by Lucien Harpress »

Yeah, part of me wouldn't hate it if I replace a good chunk of the crank and pistons. The motor has always been pretty buzzy, and for the 15 miles I had the rebuilt engine on the road no part of that changed. About half of 750 owners say this is normal, but there's the other half that say this isn't. If I've already got a boogered crank, maybe it's a good thing I've got an opportunity to replace it. I don't know.
1997 Valkyrie- Light Cutomization, but Too Busy Riding
1980 KZ1300- Bike's Haunted
1976 GL1000 (Yellow)- It Runs (Poorly) and Doesn't Leak (Mostly)
1974 Velosolex 3800- Better Than Walking
1972 CB750- Broke the Chain And Ate the Motor
1969 CT90- The Most Fun You Can Have on 90ccs.
1965 CA77 Dream- Needs a Full Teardown, but Complete

All advice I give is only valid until an expert corrects me.
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Lucien Harpress
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Re: CB750 K0/K1 Hybrid

#358

Post by Lucien Harpress »

I've been having a nice long think about things, and after a couple days of following facebook marketplace, calculating mileage and seeing what replacement engines are available, I came to a conclusion.

No matter what, I'm probably tearing back into the engine I got. If only to move the top end over, this, that, the other- no matter what I do I'm going to have it taken apart down to the bottom end regardless. And if I'm that close, why not crack it open to see what I've got going on? And if I've got it apart? Let's be honest, bearing shells are cheaper than a replacement block. Even if I just buy a couple of the loosest bearings available and swap them in until I find my tight spot?

Basically, there's lots of '76-'78 engines out there in various states of disrepair, but not really anything older. The cases I have "match" the frame I've got, and I don't think I'm getting any better. And even just with paint, I put a lot of work into this. If it IS just crank bearings (and even if it isn't), this might be the best I get.

This just means I gotta get set up to pull this motor AGAIN. (But that was the plan regardless)
1997 Valkyrie- Light Cutomization, but Too Busy Riding
1980 KZ1300- Bike's Haunted
1976 GL1000 (Yellow)- It Runs (Poorly) and Doesn't Leak (Mostly)
1974 Velosolex 3800- Better Than Walking
1972 CB750- Broke the Chain And Ate the Motor
1969 CT90- The Most Fun You Can Have on 90ccs.
1965 CA77 Dream- Needs a Full Teardown, but Complete

All advice I give is only valid until an expert corrects me.
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Rednaxs60
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Re: CB750 K0/K1 Hybrid

#359

Post by Rednaxs60 »

Bringing an older bike to life is a trial and error issue. Agree with your keeping the engine, never know what you get when you just replace old with old. Gotta love these old bikes. Good luck. Enjoying following. Looks good.
"When writing the Story of your life, don't let anyone else hold the pen."

Ernest

1985 GL1200 Limited Edition
2014 Can-Am Spyder RT LE
2021 Royal Enfield Himalayan
1995 GL1500 SE CDN Edition (sold)
2012 Suzuki DL1000 VStrom (sold)
Ontario 1985 GL1200 Limited Edition (sold)
2008 GL1800 (sold)
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Lucien Harpress
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Re: CB750 K0/K1 Hybrid

#360

Post by Lucien Harpress »

After giving things a few days to marinate, I figured it was time to dive back into this mess. I'm not looking forward to pulling this engine again (especially with the rest of the bike together AND with a paint job I don't want to ruin), but it's gotta be done.

Image

I went though the old oil as well, and sure enough, it looks like I struck gold- little shiny yellow flakes as far as the eye can see. Annoying, but hopefully fixable. Guess I'll see when I get it apart.
1997 Valkyrie- Light Cutomization, but Too Busy Riding
1980 KZ1300- Bike's Haunted
1976 GL1000 (Yellow)- It Runs (Poorly) and Doesn't Leak (Mostly)
1974 Velosolex 3800- Better Than Walking
1972 CB750- Broke the Chain And Ate the Motor
1969 CT90- The Most Fun You Can Have on 90ccs.
1965 CA77 Dream- Needs a Full Teardown, but Complete

All advice I give is only valid until an expert corrects me.
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