Topic: Repair it or cut my losses?

[Bankerdanny]

I'm not much for ape hangers, but that is a great looking bike. I love the ammo battery box.

[Stev-o]

Hey Five - how far is Hot Lanta?  Go.....


http://atlanta.craigslist.org/atl/mcy/3546146823.html

[fivestring]

Wow! That's quite a collection!!

Atlanta is 4 hours north of me. I think I'll at least see what he is asking for an engine. 70-78 would work, right?

[Stev-o]

Yes, but the K7-8 have a different, longer, output shaft on which the sprocket is mounted.
It can be made to work, just a few additional parts may be needed.
Do you have the 630 chain?

[iron_worker]

If it was idling away and that was happening inside the engine would it not sound like absolute sh!t? You'd think there would be some knocking or something.

I've never heard or something just exploding like that at idle. Seems weird to me.

IW

[fivestring]

I agree iron.  Thinking back, I was adjusting the needles with shims. I had just tried shimming them way rich too get an idea of how far I needed to go. I.e. I knew how it ran with no shims and I then knew how it ran with too much shim. On that test run on the lift in the garage the engine bogged down or 'labored' till it stopped. I thought it choked out from being too rich but now I think it was beginning to seize. I did hear a pop back through one carb ocaasionally but I have open exhaust so any other internal sounds are somewhat masked as I am also in a steel building. I am anxious to part the case and see what got chewed up. It may be a week or so till I have time to wrench. I'm hoping I can replace parts and repair this engine as it was running strong.

So it sounds like I need to stick with 77-78 engines/parts. Yes I have the big 630 chain.

[fivestring]

So I would need to move to the smaller chain and sprockets to make an earlier motor work? Or swap out shafts?

I am waiting on a reply from Atlanta on engine availability.

[70CB750]

No, you would need to alternate the rear sprocket carrier.

Look for this: Cycle X Offset Rear Sprocket The Highest Level

Here:

http://www.cyclexchange.net/Chain%20Sprocket%20Page.htm

Best explanation out there.


Your K8 has the rear sprocket further out - means 77-78 engine drops right in, for 70-76 to get the sprockets line up you need to alternate the rear sprocket.

Also swing arms can be changed around with some alterations  - http://forums.sohc4.net/index.php?topic=115305.msg1299318#msg1299318

[scottly]

No, you would need to alternate the rear sprocket carrier.

Look for this: Cycle X Offset Rear Sprocket The Highest Level

Here:

http://www.cyclexchange.net/Chain%20Sprocket%20Page.htm

That looks to be the cheapest and best way to fit an earlier motor to a K7/8 bike. The off-set front sprockets cost around $70, IIRC, and increased the load on the counter-shaft bearing. While this rear sprocket is meant to move the sprocket further out, if reversed would move it in the necessary 10mm, and is on sale for $49..

[lucky]

K8
I bought the bike for $200 a few months ago, put a bunch of weekends and another $300 in parts into it.  Yesterday I was tuning the carbs and had it idling to warm up the engine and it just shut off.  After some checking, I realized the motor seized.

I have signs of oil present in the top end, fresh oil and filter change.  The oil pump was working Friday night after a short ride I could feel the warm oil in the tank and the oil light always went out immediately on start up. I pulled the plugs, stator and clutch yesterday and the crank still is locked in either direction.  Cam chain and all rockers seem to be in place but I haven't removed the engine to take cover off yet. So I am on the way to pulling the motor out.

Friday night I took it out for a spin and it ran well, although it needed a little more gas at mid/upper range.  I punched it a few times in the driveway and it broke the back tire loose easily.  It was nearly completely road ready and this happens.

At this point I am wondering if the bike is worth an engine tear down.  The chassis and all exterior parts are in need of stripping and paint, it still needs fresh tires but that's about it.

The fact that the top end looks ok would point to a crank/rod situation and I don't have several hundred $ to sink into a bike that will never be worth the cost of repair.

I guess I'm just venting.  Had this happened when I first started working on it a few weeks ago, I wouldn't have minded as much.  It's better that it happened in the garage than on a road trip but it is still disheartening.

Any thoughts?

Who said it wasn't worth the cost of repair?
Maybe give it to someone who does not have as much money and will take the time to rebuild it.

Please do not throw it in a scrap yard! The parts are needed by the 750 community

[70CB750]

What Lucky says.

[Bailgang]

+1 on what Lucky said as well.
I know what it's like when you invest your time and $ into something only to have it fail due to some other problem you weren't aware of and you just want to wash your hands of it but trust me, you'll be doing yourself a big favor by NOT tossing anything. Getting a used engine that's in good shape is probably the most cost effective alternative but just be aware of the sprocket alignment issues as mentioned above when using a 76 and earlier engine in your K8. I'm having similar issues with a 77 K7 engine that's going in my kids 73 750 frame and my son just recently ordered the offset rear sprocket from cycleX to address that. As far as you old engine, take it apart when ever you have some free time to see what exactly went wrong and then decide whether you want to rebuild it, save the existing parts as spares or part it out to those of us who need parts. What ever you do just don't haul it to the scrap yard out of frustration.

[fivestring]

Ok, you saved it from the car crusher. 

I got a chance to open the case and have a look.  The crank and rods are pristine, even the bearings are a lovely smooth gray.  Not surprising for a 24K mile motor, I guess.

I haven't pulled the top end apart yet but will do so as time permits. I will definitely post pictures when I do.  Carnage photos are always interesting.

I am getting over my pity party somewhat and am looking at repairing this motor if the case is good.  I like the 77-78 sprockets being a little more offset in case I wanted to go a wee bit fatter on the rear tire so I'll try hard to keep it like that. And I like the hefty 630 chains just for the look. 

I intended to get her running THEN tear it down for a complete cleaning and fresh seals, etc.  I guess my plans got rearranged.

Meanwhile I am still trying to find a motor.  I have a couple leads on some old bikers in my locality that are reported to have some stuff stored away.  And I'm not in a hurry.  I have plenty of other stuff that needs my attention.  And I always have my beloved KZ if I'm jonesing for a ride. 

Thanks for the support.

[iron_worker]

So you pulled the bottom case off before you pulled the head and cylinders?

Interesting approach.

IW

[Jerry Rxman Griffin aka MuthaF'er]

+1 on what Lucky said as well.
I know what it's like when you invest your time and $ into something only to have it fail due to some other problem you weren't aware of and you just want to wash your hands of it but trust me, you'll be doing yourself a big favor by NOT tossing anything. Getting a used engine that's in good shape is probably the most cost effective alternative but just be aware of the sprocket alignment issues as mentioned above when using a 76 and earlier engine in your K8. I'm having similar issues with a 77 K7 engine that's going in my kids 73 750 frame and my son just recently ordered the offset rear sprocket from cycleX to address that. As far as you old engine, take it apart when ever you have some free time to see what exactly went wrong and then decide whether you want to rebuild it, save the existing parts as spares or part it out to those of us who need parts. What ever you do just don't haul it to the scrap yard out of frustration.

I recently spoke with a nice lady at SprocketSpecialist.com about a front conversion sprocket for the 78 K engine I'll be installing in a 75 750F. She said they do have them. Made in the US too. Out of stock a week ago. ~ $25

[fivestring]

I got time to finish breaking down this motor to find what locked it up.  I had said previously that the bearings were 'pristine'.  Well, not quite.  I had only pulled #1 rod cap off.  As it turns out, #3 was hiding some secrets.



All three of the other rod bearings basically fell off their positions easily when the rod cap was removed.  the #3 bearings had to be peeled off the crank.



So the crank will need some machining on that journal.  I am not a machinist, but it doesn't look terrible.  I'm hoping undersized bearings are an option if it needs to go that route.  Or I could get another crank and drop in it.

Here's #1 rod bearing for comparison.



Any ideas what may have caused this bearing to deteriorate?

I think this is what caused the lock up.  You can see in this next picture there is a small chunk missing from the end of this shell...



And here is that little missing sliver sticking to the other half of that rod bearing....



I would like some input on what you guys think I should do to be sure it will be good to go when reassembled.

[Kickstart]

Do all the bearing shells have a lip like that on the side?
None of mine do, but I have a 75... not sure if the 77/78 was different. Was the engine previously rebuilt?... maybe a PO used an incorrect bearing shell.

Regardless, that shell is obviously shot.  How does the corresponding journal on the crank look?  can you measure the journal.  I would guess that if the journal isn't worn too much, you can get a new (thicker?) shell and be good to go.  But, the shells don't go all that thick, so you may have to get a new crank if the journal is worn past it's limit.

[scottly]

That is a classic example of a spun bearing; it is galled on both the ID and OD, most likely do to lack of oil. (Once it first spun, there would definitely be a lack of oil.) The crank is probably toast; cheaper to replace than resurface, and under-sized bearings aren't available anyway. The rod is probably toast as well. Is the big end a pretty shade of blue?      

[fivestring]

I'll look closely at the rod in the morning.

That lip is unique to that one bearing.  I believe the lip is a result of the bearing being spun and not supposed to be like that.

[Gregorymoto]

I say find another motor, if your in Nor Cal. I have a motor you can have for $150. The bottom end is real good. The only bad is the #4 cylinder is rusted. But I have another set of jugs ready to go. Easy rebuild.

[fivestring]

I say find another motor, if your in Nor Cal. I have a motor you can have for $150. The bottom end is real good. The only bad is the #4 cylinder is rusted. But I have another set of jugs ready to go. Easy rebuild.

I'd take that deal if I were in your area.  I'm having some difficulty finding a good deal on a good motor.  I'm checking more into repairing what I have because the case seems to be ok.