Author Topic: Guidance needed: Engine seized up, third piston stuck, heavy wear on the crank. (Read 9035 times)

jacquesleclochard · « **on:** June 14, 2013, 04:18:41 PM »

From the get go: my CB750 build is a kickstart only, and uses the kickstart as a sidestand. Design flaw; pipes are bent snug along lower frame tubes, so no room for a sidestand. It works.

As I was eliminating the electrical gremlins, I had the bike running. All was good. It kicked over nicely, and with good compression. At a certain point, it didn't kick anymore.

Took the clutch plates out, and the kickstart turned over again. When I put it back, it locks up. And the crankshaft is locked in place. Doesn't budge. I tried removing the electric starter, tried moving the bolt at the ignition plate, nothing.

Since I bought the bike, shifting gears has been very easy. Without too much trouble I can kick it into next gear, and the bike now rolls freely in all 5 gears. The gear mechanism is in working order.

Taking this last information in account, what do you think it is? Will I have to open up the cases, and look at the transmission? I'm out of idea's to try on the outside.

bollingball · « **Reply #1 on:** June 14, 2013, 05:31:35 PM »

Quote from: jacquesleclochard on June 14, 2013, 04:18:41 PM

From the get go: my CB750 build is a kickstart only, and uses the kickstart as a sidestand. Design flaw; pipes are bent snug along lower frame tubes, so no room for a sidestand. It works.

As I was eliminating the electrical gremlins, I had the bike running. All was good. It kicked over nicely, and with good compression. At a certain point, it didn't kick anymore.

Took the clutch plates out, and the kickstart turned over again. When I put it back, it locks up. And the crankshaft is locked in place. Doesn't budge. I tried removing the electric starter, tried moving the bolt at the ignition plate, nothing.

Since I bought the bike, shifting gears has been very easy. Without too much trouble I can kick it into next gear, and the bike now rolls freely in all 5 gears. The gear mechanism is in working order.

Taking this last information in account, what do you think it is? Will I have to open up the cases, and look at the transmission? I'm out of idea's to try on the outside.

Just how do you do this The spring keeps the kick start up. Do you kick it down and then lean it over ? Then get off on the right side. With the bike leaning to the right I bet it gets some second looks. I wonder if the pressure on the kick shaft has something to do with the problem? Do you leave it running and get off the bike while it is leaning on the kicker?
Ken

ekpent · « **Reply #2 on:** June 14, 2013, 05:39:46 PM »

I am having a hard time getting my head around the kickstart/sidestand thing. Have a picture of it in action ?

bollingball · « **Reply #3 on:** June 14, 2013, 05:57:14 PM »

Quote from: ekpent on June 14, 2013, 05:39:46 PM

I am having a hard time getting my head around the kickstart/sidestand thing. Have a picture of it in action ?

The more I think about it the more I can't stop grinning

I would love to see it. I'm trying to think if it would do any harm and be related to his problem. I have been riding since 65 and never heard of anyone ever doing this.
Ken

Dream750 · « **Reply #4 on:** June 14, 2013, 06:16:46 PM »

Then there’s the old motorcycle trick of using the kick starter as the kick stand ...

Terry in Australia · « **Reply #5 on:** June 14, 2013, 08:39:52 PM »

If it'll roll freely in gear and the drive chain is still connected, I'm guessing that you've busted your primary chains. By removing your clutch plates you've disengaged your kick starter from the rest of the mechanism, so if follows that the kicker, which is geared to the clutch will turn, but the crank won't.

The reason that your crank won't turn (and don't put any pressure on the "Bolt" on the points shaft, or you'll just snap it off) is because it's probably got the bulk of your promary chains jammed between the crank and the bottom case. Yes, you'll have to pull it apart, and if I'm right, it'll be ugly. Cheers, Terry.

jacquesleclochard · « **Reply #6 on:** June 14, 2013, 11:19:08 PM »

How would the primary chain get involved in this, Terry? Bah, let's hope not; I have four engines out now, dismantled, and this isn't exactly cleaning up the shop. What needs must be. I'll take off the oil pan first and then see what is visible at the bottom.

Something else I remembered yesterday. The forward rockers received oil. The rear ones didn't. Might have seized up the pistons?...

Terry in Australia · « **Reply #7 on:** June 15, 2013, 01:15:43 AM »

G'Day Mate, yep, if it wasn't for the fact that you said you were able to shift thru all the gears with the bike rolling, I would have suggested that you'd either seized your engine or perhaps dropped your camchain. (or even broken your cam, which has happened here before)

The only way you can shift thru the gears with the bike rolling but the crank locked up, would be if the clutch shaft was disconnected from the crankshaft, meaning that either your primary chains have somehow come off their sprockets (unlikely) or have broken.

Drop your oil pan, and all will be revealed!

jacquesleclochard · « **Reply #8 on:** June 27, 2013, 09:41:32 AM »

So I took it apart, but not after checking the head first. When I removed the oil filter, it didn't leak a lot of oil. When I noticed this I started wondering: did the head get enough? If any? It looks like it, but still it is a bit try. Took a picture of the head.

Flipped it over and split the cases. Interesting wear on the crankshaft. What do you think caused this?

The transmission doesn't seem to have any kind of wear, but, to be honest, I don't know what to check really. (Someone has my Hondaman book lying at home - need to get it back!)

The teeth on the primary chain gears look worn. Thoughts?

And still the pistons are seized. They should turn over now, right? If so, should I take a look at the oil pump?

iron_worker · « **Reply #9 on:** June 27, 2013, 10:18:18 AM »

That top end is looking quite dry... I'm thinkin you seized the pistons or the cam... or both? If the crank won't turn with the lower case removed then you for sure one of them.

IW

jacquesleclochard · « **Reply #10 on:** June 27, 2013, 10:20:51 AM »

That's what I was thinking... Heck.

Oil pump malfunctioning, or clogged up oil passages?

Old Scrambler · « **Reply #11 on:** June 27, 2013, 11:08:43 AM »

You said you had the engine running...........then it would not kick anymore. Did you have it on the road.....or just in the shop? Looks very dry ...........is in .......DID YOU PUT ANY OIL IN THE TANK? Mr Honda and the crew would drain the oil from test motors in the factory.......start them up..........go to lunch.......and they were still running without damage with only the residual oil (about a liter) in the motor. Your oil pump is probably air-locked or not functioning. Your motor appears to have had a hard life........did you find any metal chips in the drain-oil? Before you try to rotate the crank or pull the rods.........pull the cam-tower off and check the cam bearings. With no or minimal oil they are usually the first thing to 'run dry'

jacquesleclochard · « **Reply #12 on:** June 27, 2013, 02:01:22 PM »

I will look at the bearings. Yes there was oil in the engine, and I did run it around the block. Reading up on the oil pump... Interesting to learn it is attached to The kickstart sprocket.

jacquesleclochard · « **Reply #13 on:** June 28, 2013, 05:38:22 AM »

Measured the shift fork fingers. Is this one below speficiations? According to HM it is; minimum 0.240. Is this wear the cause of jumping gears?

jacquesleclochard · « **Reply #14 on:** June 28, 2013, 05:59:35 AM »

Iron wool in the pan, nothing else. Found some metal shavings around the crankshaft. Im going to check the pump.

bjatwood · « **Reply #15 on:** June 28, 2013, 07:39:50 AM »

Quote from: jacquesleclochard on June 28, 2013, 05:38:22 AM

Measured the shift fork fingers. Is this one below speficiations? According to HM it is; minimum 0.240. Is this wear the cause of jumping gears?

Yep put a new shift fork on it. Had this same thing happen to me on a Minitrail 70 4 speed motor. Specs are specs for a reason. Do not ever button it back up without everything in HM "spec" or, you'll be tearing it down again.

jacquesleclochard · « **Reply #16 on:** June 28, 2013, 07:51:29 AM »

Took out The kickstart and replaced the sprocket. How the HELL do I reinstall this spring?!

jacquesleclochard · « **Reply #17 on:** June 28, 2013, 08:08:07 AM »

Yes! Two man job. Used a piece of rope, went smooth.

jacquesleclochard · « **Reply #18 on:** June 28, 2013, 08:21:36 AM »

Ill be ordering some new forks then. This would be the cause for the shifting problem? Still no clue on that weird wear on the crank.

Found an old oil pump lying around. Thats up for revision and ill use that when its done. Meanwhile the used pump was cleaned and drowned in oil and reinstalled. Who knows, maybe the passages to the top are clogged.

On to the top end.... Here we go, reversed engineering, bottom up!

Nikkisixx · « **Reply #19 on:** June 28, 2013, 09:21:49 AM »

Unlike the XS 650 pictured above, the oil pump on a CB is driven by a gear on the kicker shaft. When the kicker is down the sprag clutch on that gear is going ratchety ratchet, and the gear wobbles like all kinds of crazy. Janky treatment of an oil pump. Because of this I wouldn't be inclined to use the kicker as a side stand, but I'm no gambler.

In the head there are only oil squirters on the intake side of rocker shafts, so not unusual to only see oil squirting from there.

Also - If the clutch is removed, the bike can go through the gears (trans and engine uncoupled).

Duke McDukiedook · « **Reply #20 on:** June 28, 2013, 09:45:38 AM »

Yeah, using the kickstarter for a stand when the kickstarter is your only way to start the engine sounds like an absolutely horrible idea.

jacquesleclochard · « **Reply #21 on:** June 28, 2013, 12:34:34 PM »

So the day is done... Lots of new findings. Will post pictures in a second.

By the way, what XS?

jacquesleclochard · « **Reply #22 on:** June 28, 2013, 01:48:28 PM »

Here we go. I took a look at the head, the towers, and here's what I found.

There is wear on the shaft. How much damage am I looking at? Can I salvage this? Or replace it with an old shaft I have lying around?

The towers look slightly polished.

These oil seals, what to make of them?

But there is more......

jacquesleclochard · « **Reply #23 on:** June 28, 2013, 01:52:46 PM »

Now here comes the fun part.

Third piston was stuck. The connecting rod had jammed itself. Look how dry it is.

The inner side of the piston was dry as well. The wear on the pin, is that normal?

And look at the wear at the bearings, and on the crank itself.

jacquesleclochard · « **Reply #24 on:** June 28, 2013, 01:59:03 PM »

This is where I left the project. I couldn't split the cilinder head, so no inspection was done on the sleeves. However, this really looks like a lubrication problem to me. What do you think caused this heavy wear to the crank? Defect oil pump? And is the top end, the cam, still salvageable?

What IS still salvageable? The pistons? The connecting rods? They look worn as well.

I kind of need some guidance here..... to be honest... Help!

I have two spare engines lying around, both donors (dismantled and damaged). A replacement crank and cam are around, so that is nice. I have a spare case as well.

The balance after day two:

New bearings for the crank
New shift forks

News:

Author Topic: Guidance needed: Engine seized up, third piston stuck, heavy wear on the crank. (Read 9035 times)

bollingball

bollingball