Getting Cranky

[tz375]

This a cautionary tale for anyone who buys a bike with a rebuilt crank.

Before I stripped this motor form a low mileage bike that had been rebuilt recently with a rebuilt crank, I did a compression and leakdown test. Compressions wasn't spectacular and leakdown was hard to get a consistent reading because of poor sealing at the block off plugs - or so I thought.

The last rebuild was only a couple of years and a few thousand miles back and it was flooded in oil, so it was going to be fine to use.

Well, just in case, I poured a whole lot of bright blue oil into each crank chamber - almost to the crankcase mouth and left it for a few days. No leaks at the two outer seals - Yeah. But today I see blue oil starting to seep out of thr transmission housing (the clutch is off and the trans was drained of green-black oil, so this is clearly coming past the crank seals.

It doesn't much matter which side it's coming out of - unless someone used an old style seal.

So the lesson of the story is even if it was rebuilt, your crank may be shot, so check it. In this case it is now a 100% record of leaking cranks and the other rebuilt one is full of rust.

Go to a reputable crank rebuilder. When I get this one drained and stripped, it's off to Bill Bune.

[Spamy]

The crank is bad or the seals? A bit different I would think. What bike is this on?

As far as the GT550, the seal that would leak into the tranny would be the primary sprocket side seal only, which should be one bearing removal and a new seal. About $500 bucks cheaper than a crank rebuild.

A leakdown test with the intake, exhaust and SRIS plugged off?

Well, hope you get some good news out of the motor somewhere.

[tz375]

Last night I split the cases and pulled the crank out.

It is hard to see what's actually failed. The right seal looks OK (ish) but the crank nose is slightly pitted where the seal runs. On the left cylinder the seal can be moved away from the normal position and it appears that the crank is pitted there too.

What it is starting to look like is that the crank was rusty and the guy that rebuilt is cleaned it up and fitted new seals, but they are not sealing properly. I bought a rebuilt crank from the same guy and it is also rusty. I'm not blaming the seller. Either the crank rusted in storage from sitting around too long without adequate protection or the crank builder did a less than stellar job of inspecting the crank pieces when he stripped it and fitted new seals.

I have already stripped and scrapped 2 cranks and one gave up the oil slingers and the rest was all too rusty to use. It happens. Fortunately I have another couple of cranks to use for parts, but at some point, we'll all have to find new crank parts of find a way to get the rust repaired.

My take on this is that all my cranks (not in motors) will be flushed with oil, wrapped and sealed in moisture tight bags. The good news is that any crank parts that turn out to be rusty can be scrapped and that might clear some space in the shop.

[yeadon_m]

Richard,

Thinking aloud and for the distant future, it is possible to get the pitted piece hardchromed and resized / returned to service? I have no idea what finish or treatment the OE metal had.

Cheers,
Mike

[Alan H]

A slightly different take on cranks.

When I decided to do the GT550, I decided to try and avoid a complete strip & rebuild if possible, so I lifted the head & barrels (barrels & pistons weren't too good) and fill each crankcase with diesel. I turned the engine over on the kickstart (not too quickly though) over a period of several days, then drained and refilled and did it all again with the hope that the diesel would soften the seals and also any rust on the crank seal facings.
Pumped loads of oil through the CCI tubes and over oiled everything I could, so it was a pig to start, but eventually settled down and has run OK since.
It seemed to work for me anyway and the bike runs well 1500 miles on. Similar performance to a mate's T500 and would be a bit better if I could be arsed to take the carbs off and cure the slight flat spot at about 1/3 throttle. This will be a winter job!

It may not work every time, but may be worth a try, just to avoid the total strip & rebuild costs.

[tz375]

All great input. This motor is now completely stripped and I am sorting through cranks to find the best one to send for rebuilding.

At some point in the future I expect that we will need to start repairing cranks where the seals run. On the ends, it's relatively easy to get a short bearing sleeve, so that might be one avenue. The shaft ends don't appear to be hardened, so it should almost be possible to bronze weld and machine them or have them plasma sprayed and ground.

For this project I have options - In fact I think I have managed to corner the Midwest supply of old cranks.

The real point of the story is that just because a crank has supposedly been rebuilt, doesn't mean it is actually any good. The crank parts need to be very carefully cleaned and inspected before the crank is assembled with new seals.

[tz375]

Update: Bill Bune just finished the crank using the ends form a spare (donor) crank.

Not only was the end of the shaft badly pitted, but it turns out that the crank was out of phase ie it had been assembled and trued badly.

At least that gets rid of some more junk metal to be recycled into garden furniture or boat anchors.

While the crank was out I took a few minutes to check out the crankcases. The bottom half was a mismatched 72-3 case with a 77 top half. Selector cam was also pre 74 and the water pump is the early style too, but the transmission appears to be M-A ratios but I need to double check and inspect the gears and dogs.

Mike, At some point we will have to start welding and repairing parts. It should be possible to grind them down, plasma spray them and grind back to size. I also looked at seal sleeves which might work as an interim fix.

[tz375]

The voyage of discovery continues.

Today I removed the water pump cleaned and inspected it in more detail. The drive gear and matching gear on the quill shaft show massive wear and that's unusual, so I looked a little closer. It is a very early water pump with a woodruff key and it has been rebuilt at some time in the past. The oil seal is the same type I use and the graphite part of the mechanical seal looks good but the steel part is badly gouged suggesting that one part was replaced and not the other.

I tried to put the shaft in the drill press to spin it and it wobbled badly, so I had another look. The top had been struck with a hammer and has a nice bump on the side of the shaft
. Obviously that was the cause of that wear - the end was tight in the bush in the upper crankcase half, so I flipped the upper case over and there is no bush. It's not there.

So the shaft must have been flopping about and that was what caused the wear on the gears.

The waterpump shaft and quill shaft are too badly worn so they are going to the great recycling depot in the sky.

I can build a waterpump from others I have but this is getting silly.

What secrets will it give up tomorrow?

[yeadon_m]

Sorry to hear of your forensic type findings (hopefully not an autopsy!).
Its a reminder to us that often (not always) the best resto prospects are unmolested examples no matter how bad they look on the outside. My own original GT380 which I'd owned for decades was a breeze, the GT550 which had been hacked about was / is far from that. Bodger city inside.
Good luck!
Mike

[tz375]

Thanks Mike,

I'm not upset or dismayed - just a little surprised, but I tend to be a little anal and I like to do the autopsy thing.

Like most things in life, it's all about the story and it's my way to get the bike to tell its story and reveal some part of its past. And this is as much about sharing the story as it is about identifying problems that others could watch out for.

We all make mistakes and hopefully learn from them as we go.

[Suzsmokeyallan]

I once got a water pump in with a bunch of small parts for practically nothing and decided to rebuild the pump. There was this thin ring around the cartridge body with the circlip as the impeller was still on the pump. On closer inspection the shaft end was mushroomed by the gear so I looked at that ring to see what it really was next to the circlip.
SOMEONE in removing the cartridge from the lower crankcase brutalized the pump shaft trying to remove it and that 'ring' was the piece of crankcase casting below the circlip that was blown out in the hammering.
No comment can really be made to justify this sort of ham fisted ignorance.

[tz375]

It could have been worse - you could have bought the crankcases

Actually, I'd be surprised if that doesn't happen more often as people struggle to get the pump out and don't know that there's a large circlip hiding under the impeller.

[tz375]

Crank arrived back, along with what was left of the donor crank. They had to replace one end wheel, two bearings and all the seals in what was a crank rebuild not many mile sago by another person. Fortunately, most of the rest of it was fine. One side was around about 8 degrees out of phase though.

Looking at a spare old style crank I can see rub marks on one of the rods. I'll take another look at that and see if I can work out what that was caused by. I know what it was rubbing one, just not why it was rubbing. I'll get back on that.

[tz375]

Well I was wrong. The transmission inside those B cases turned out to be an J-K-L transmission. So effectively the whole bottom end was probably a K except for the top half of the crankcase which was from a B model.

I think I finally cracked the code on cranks and should probably add a page to the Pinkpossum site.

I have one J-K crank with a later Rod on it and if that was used with an early style piston the rod can float excessively at both ends and may rub on a crank wheel. Not good.

It looks like that may have been the cause of failure of at east one conrod documented on this site a couple of years ago. I'll keep digging..