Topic: Help with new CB650 Project

[grcamna2]

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[newday777]

Slow down. You’re all over the place.

The crack in the case is the indication your issue is with the starter clutch. You can remove the cam chain without cutting it by rotating the crank to access the 2 bolts holding the cam sprocket to the camshaft. Once you’ve done that, release the tension and slightly raise the chain straight up, then slip the cam to the left to clear the sprocket.

Before removing the camshaft, tie up your cam chain with some zip ties to prevent it falling into the cavity.

Then you can start removing the oil pan and looking up to understand more of the damage.

You can’t buy “cases” unless the bearings match your crankshaft. But whole cases as a matched set (or another motor) are in your future. Sorry about your bad luck 

His motor is seized. He can't rotate the crank or the cam.

[newday777]

I guess my question is, now what?

If it was sitting in your garage what would you do with it? I’ve got more time than money and don’t mind a project.

Get another motor, another donor bike.....

[calj737]

Something wanted out. If it wanted out at 10,000 rpm, it won’t be good…

It wouldn’t even need to be at 10k RPMs. 2-3k is plenty of inertia to trash a motor. If the underside of the cylinder head is undamaged, then it wasn’t a rod that let go. But a full teardown is required to adequately diagnose and repair that motor (if doable).

[bryanj]

With the engine out and side cases removed along with all the clutch and gearchange parts you can separate the lower crancase to find whats exploded and probably unjam the crank to rotate and strip out cam, head and cylinders.
In the end a different engine will probably be cheapest option BUT if you strip this one first and top end is good you could look for just a bottom end which may be cheaper

[fizzlebottom]

If I were in your shoes, I probably wouldn't bother tearing this thing apart and doing any repairs. I would sit on eBay and wait for a reasonable motor to pop up. I already did this a few years ago and my eBay motor has been running perfectly since then.

Here's my reasoning: Whatever blew the hole in the case also threw debris all over the internals. If that debris clogged up any oil passages, you may have burned up bearings. If that debris got into the bearings before clogging up oil passages, you may have burned up bearings. If that debris got up to the cylinder walls then you may have to overbore. Boring and pistons aren't a big deal, but bearings sure can be. Especially crankshaft bearings, because they're nearly impossible to find for the CB650 motors. If the camshaft bearing surfaces are messed up, game over until you replace the cylinder head cover.

Add up all of the time and money on both parts & work sent out to shops and you may be paying for a new motor. It is a risk to go down that rabbit hole, and also a risk to buy a used motor. But I'd rather start with a complete cosmetically undamaged motor that spins to work with instead of one that needs critical repairs off the bat.

Others may disagree, but that's my take.

[bryanj]

I agree, but the mechanic in me wants to know exactly what went bang

[76 Supersport]

Ta-da! (See attached pictures)

[76 Supersport]

Although I want to feel special (first time anyones seen a primary chain break) I think the chain is the chicken and not the egg here.

[newday777]

That tensioner doesn't look so healthy either. Can you spin the motor any now to access the cam sprocket bolts?

[Tracksnblades1]

Something wanted out. If it wanted out at 10,000 rpm, it won’t be good…

It wouldn’t even need to be at 10k RPMs. 2-3k is plenty of inertia to trash a motor. If the underside of the cylinder head is undamaged, then it wasn’t a rod that let go. But a full teardown is required to adequately diagnose and repair that motor (if doable).

Agree…..

But centrifugal forces square as the rpm goes up….Too bad the photos  aren’t good enough for “the rest of the story…

I’m betting the max rpm for the 650’s  Hyvo chain isn’t much above its tachometer’s redline..Ramsey Chain has all the engineering specs for the Morse type Hyvos.  Limiting High Rpm centrifugal forces usually exceed the tensile strength of the chain…

Bear, the wizard from Oz, has mentioned his findings Dohc Hyvos in Sohc strokers’ limiting his engine’s rpms. Even with frequent regimented inspection and tear down schedules  the Hyvo chain was the fuse…

Im thinking the cb350 had the highest redline of the sohc hyvo’s….

Looks like Bryan J hit the nail on the head…with the cracks high and low I knew it wasn’t going to be an economical fix..
I still don’t think we know the real story….

[76 Supersport]

Everything I could get out. Going to try and rotate motor.

[Tracksnblades1]

Everything I could get out. Going to try and rotate motor.

Bet it made that oh so familiar but disappointing “Shuuunnk” sound when it wanted out…

[76 Supersport]

Still not budging. So clutch and everything out of the transmission, then try and get some case halve separation? Is there anything that I should do while the motors still in the bike? I.E. crack head bolts


Here are a couple horrible pictures from under the bike.

[76 Supersport]

We’ll I’m humbled again.. as the worlds biggest dumbass I think I have found the rest of the story..

See pictures…


Second picture is the screen to my borescope it appears to be an (end cap?) wedged between the crank and rod arm.

[calj737]

There’s not a lot of reason to disassemble that motor any further. It has suffered a catastrophic event and is beyond repair. Sh!tty that the PO didn’t disclose the truth or you didn’t get a chance to investigate more fully the condition of the motor.

Good news is: you “can” replace the motor pretty easily with another 79-82 650 motor. The carbs differ between the 80/81 motors so bear that in mind. Another option is a 500 or 550 motor will bolt in. You’d lose some power based upon stock specs, and the 500 has a slightly different RR motor hangar because the clutch is on the left side. (Just listing options).

If you want a storm trooper of a motor, I have a full tilt 500 that is an over the top motor you could plug in. It will make more HP than the stock 650 by a good bit.

All in all, a crappy way to get started in your first SOHC. 

[76 Supersport]

Thank you for the advice. On the bright side with the starter off and the stator off there’s only three bolts left to drop the motor.

What’s a good price for a 650 motor? I see some in the  5 to 7 hundred range on eBay.

[Tracksnblades1]

Thank you for the advice. On the bright side with the starter off and the stator off there’s only three bolts left to drop the motor.

What’s a good price for a 650 motor? I see some in the  5 to 7 hundred range on eBay.

I was wondering if that was what wanted out.. Especially reading the head and the cases were broke..At least you know “the rest of the story”. And what caused the Hyvo chain failure.

One would believe the rider would of heard a warning…but sometimes all you get to hear is that dreadful shhuunnk…

Good you found your issues… Perhaps you can hear the donor bike run prior to the purchase …Good Luck…

[grcamna2]

Thank you for the advice. On the bright side with the starter off and the stator off there’s only three bolts left to drop the motor.

What’s a good price for a 650 motor? I see some in the  5 to 7 hundred range on eBay.

You may find a very good deal on an 82' CB650 (sohc) Nighthawk complete bike over the Winter;a person may have one and 'word of mouth' you find out they just 'want it gone'.
I would imagine you could verify the engine's 'free' (not seized)by putting the bike up on the centerstand and putting it in 5th gear and turning the back wheel,even if it's presently not running.

Honda came out with the 83' CB650SC Nighthawk in 83' and everyone forgot about the earlier SOHC 650 Nighthawk in favor of the 83-85' models;deals can be found.

[fizzlebottom]

Thank you for the advice. On the bright side with the starter off and the stator off there’s only three bolts left to drop the motor.

What’s a good price for a 650 motor? I see some in the  5 to 7 hundred range on eBay.

I paid $600 after shipping for mine and felt like it was a fair price.

[76 Supersport]

Found a couple eBay listings. What do you think shipping will be from east - Mid East to California? 2-300?
Messaged both sellers for a Quote so I guess we shall see.

https://www.ebay.com/itm/325366629610?hash=item4bc15cc4ea:g:0GoAAOSw11RjJQW~

https://www.ebay.com/itm/235041491259?campid=5338992317&mkevt=1&mkcid=1&toolid=10050&customid=&mkrid=711-53200-19255-0&campid=5338992317&mkevt=1&mkcid=1&toolid=10050&customid=50b0f978b81e16cec1799c12307c009a&mkrid=710-53481-19255-0&msclkid=50b0f978b81e16cec1799c12307c009a

Compression on second engine looks a little funky, what do y’all think?

[grcamna2]

The first engine in Romeo,MI. looks like the seller is being fair,imo.
You might see if you can work out something to get it shipped/delivered to a local(to you) business loading dock;or possibly Uship.com to your area.

[76 Supersport]

What do you all think broke first? See pictures.

[grcamna2]

I'm guessing seized piston..

[Tracksnblades1]

Yep, “the rest of the story”…

That previous owner or someone had to hear that before the light lay over before it seized…🤔

Like Bryan j mentioned about the Hyvo breaking, now you know what broke it…

Was the rod journal that it came from blue..?

 Did you find an engine…?