750 crank

rustman

rustman

Active member
Was working on an engine I picked up and got down to the crank. First thing I noticed was an extra timing mark, clearly handpunched. I then pulled the crank out and onto the bench and separated it and found it to be welded. Here is my problem, when I realign the factory timing marks the crank is outta phase but when i use the "new" timing mark it is lined up. Here is my question:

1. If a crank spun and was then welded without the gear being realigned can it still be used?
 

rustman. If I,m interpreting this correctly, than I would say yes its ok to run this crank as someone has already taken the time to figure out phasing of this crank and had the smarts enough to add the new timing mark. Just the gear slipped on the crank, and they determined how much it had moved then welded it.
 
Thanks, I was reasoning along the same lines. I just needed some confirmation. Now I just have to get the broken bolt out of the recoil end :(
 
BE CAREFUL...... I'd bet that crank still has issues!!!

Sure they may have did the best they could to index it and make an new mark but how close do you really think they got with out the proper jig? I would bet it's still off just closer than it first was when it spun. I wouldn't put it back in without having it checked!!!

My $.02

M
 
I wish there was someway I could just check it myself, last crank I sent out ended up with two bent rods. does anyone know how many teeth are on the smaller of the two crank gears? How many degrees does a crank have to be out to be harmful to operation? How does someone go about cleaning a crank? Its next to impossible to see inside the bearings, everything seems to spin smooth but I want to be sure nothing is in there.
 
Hey rustman, Curious, what's with the name "rustman"? You got the opposite of the golden touch??, Body repair guy? Just curious.

Anywho, first on the broke bolt (simple stuff first). I don't like drilling or easyouts and avoid both if I can. Drilling a steel bolt out of aluminum is a real pain. It's hard to keep the bit in the steel especially on a small bolt like you are dealing with. I weld out broken bolts all the time with a 90+% success rate. Works best with dissimiliar metals (which you have here) Clean the end of the broken bolt with a die grinder. Find, center over the broken bolt and weld a washer to it. Then tack weld a nut to the washer. Let it cool some while tapping it with a hammer. Put a wrench to the nut and give it a try. They will usually come right out. You may need to work it back and forth a bit with some penetration lube but it should come out. Some like to just weld the nut right to the bolt but I have found that I have better luck starting with the washer. I can get better penetration on the weld and will ususally have success first time out.

Second on the timing, I would agree that I would like to be safe and know what was going on. I am lucky to have a good crank guy close by so I would just run it over and have it checked. If I didn't I would get a degree wheel and a dail indicator ( two indicators would be easier) and check it myself. You can look up firing order and figure crank rotation to make sure they are all close to right with the timing marks aligned. To be precise I would assemble the crank in the case with # 2 and 3 cylinders/pistons installed. There is no need for gaskets, seals or rings here. Attach the degree wheel to either end of the crank and the dial indicator/s to the top of the cylinders so you can measure piston up/down travel. When you move the piston up and the dial quits moving mark the degree wheel somehow to the case. Keep moving in the same direction until the dial starts moving again and make another mark. Recheck this to make sure it is correct. When you have it right half way between those marks is TDC and you can get to TDC by splitting the difference with the degree wheel. Do the same on the other cylinder and you now have your bench marks for crank phasing. Those bench marks should be 90% from each other and you can check that with the degree wheel that is attached to the crank. If it's right on you should be good. If it's off (even a little) I would have it redone by a good crank guy that knows these animals.

Third, cleaning bearings. Wash with solvent and blow them out with compressed air. I brake clean them next to make sure they are clean and dry. Then rotate evey bearing feeling for any hitches or any other abnormalities. Everythng should be smooth and even. There is also dimentions in the book for side play and rod deflection. Feel and measure is about the best you can do without dissassembly. These are tough sumbitches and arn't known for having many issues with crank bearings so I don't get to worried about them if all feels/looks good. When your done just oil them up good to prevent any rust.

Good Luck, opsled
 
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opsled wow,you know your crap..When it comes to crank stuff I would just split the case and send them to Hauck or opsled for work and pay them..
 
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Opsled, great post and thanks. The bolt was broken off inside the crank so it would be very hard to use your method, there is nothing protruding out past the end of the crank. Gonna put it in the data banks though, for when I can use it. I did however find a decent machine shop who can get it out for me. I will be buying a few more tools for the sled shed I think, I assume I should be able to find a degree wheel and a dial indicator at a napa outlet or similar.

Apsley, a piston stop is just a tool I can pickup as well?

Rustman is an homage to my favourite singer Neil Young. It's kind of obscure to most Neil young listeners, but I've literally listened to everything he's ever done.
 
Sorry rustman for knowing nothing about Niel Young (so I'm still in the dark lol) and assuming your broken bolt was one of the four that bolts on the recoil housing. The one that bolts on the cup (into the crank) is bigger and being in the crank I would use a machinest too in that case. I have a good buddy that runs a small jobber shop and guys with tallent can do wonders with stuff like that in no time with no damage.

Inline, thanks for the comp but if he sent that crank to me I would just take it to the same guy that did Mikes crank cuz I would want a pro to have a look see at it.

opsled
 
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when i got my max it had a spun crank that i fixed exactly as you are describing.i removed the cranks and reclocked them as close to 90* as possable.reassembled the engine and used a piston stop,degree wheel and dial indicater to check timing.i determined that the timing was 1* out.i broke the engine back down,welded the crank,stamped a new timing mark and reassembled the engine for good.

FYI...there are 40 "teeth" on the crank gear making each "tooth" worth 9*.so after reclocking the crank,it will be out a max of 4.5*.
 
v4eva said:
when i got my max it had a spun crank that i fixed exactly as you are describing.i removed the cranks and reclocked them as close to 90* as possable.reassembled the engine and used a piston stop,degree wheel and dial indicater to check timing.i determined that the timing was 1* out.i broke the engine back down,welded the crank,stamped a new timing mark and reassembled the engine for good.

FYI...there are 40 "teeth" on the crank gear making each "tooth" worth 9*.so after reclocking the crank,it will be out a max of 4.5*.
Click to expand...

Thanks alot for that little tidbit! It makes me a little more confident that I should be ok with this crank if it was set correctly whenever it was welded. Great info on the crank gears. I could have easily counted them I suppose but still, thanks alot!

Opsled, I used your washer welding technique. I had a bolt broken off in the coolant rail where the stat sits, and using your advice I was able to extract it easily and effectively. I was pleased by how great it worked, my welding skills are not top notch, I basically bought a welder plugged it in and went at it.

This is all moving me in a good direction for rebuilding this engine(serial#000666), my next question is,

On the extremities of the crank there are two retaining clips, they are almost a full circle. On the inside ends of the crank, just before the seals to separate the crank space from the gear space, the clips that came out of my engine are only 1/2 circles. Is this normal? If so how are they seated into the case? Do they go half in the bottom and half in the top? Do they sit fully in the top of the case? I am almost ready to assemble and check for timing.

Thanks.
 
I like how Opslead determines crank position relative to T.D.C. Just like degreeing a camshaft into a 4 stroke engine. Make sure you don't move your degree wheel pointer once you start. Wondering if the crank gear is re-positioned because the spline like machineing or cuts on the crank and gear line up the crank phasing better with the gear rotated around a bit? Explaining the new timing mark?
 
Rustman... a piston stop is a handy tool to have around the shop. You can buy or make it yourself. Just gut an old sparkie of it's porcelain, and cut threads into the "hex" part of the carcass. Thread in a good grade bolt with the end rounded and smooth along with a jam nut and now you have a handy tool for engine work.
 
Hmmm, Seems I've missed some stuff here. Catch up time.

Rustman, You probably already have your answer but yes the inner crank clips are half circles. And, that welding out bolts trick is one of my favorites. Don't remeber where I learned if from and have honed it to my liking but won't forget the trick. Glad it worked for ya.

Lakeshadow. I can't take credit for that TDC method either. Even though it's standard stuff and I've always known how it is actually printed in Yamaha service manuals to do it in the same basic fasion for ignition timing on many engines.

TDC isn't when the piston stops moving up. TDC is half way between the point it stops moving up and starts moving down.

Wolfy, v4eva, Piston stop?? I've heard the term but never used one. I've worked on all kinds and sizes of engines and had to dial indicate TDC for a variety of reasons but never had an occasion to use a piston stop. Can you guys enlighten me on what a piston stop does?

Thanks, (Phil) opsled
 
A piston stop just threads into the spark plug hole and gives the piston something to touch against for a solid stop position. You turn the crank one direction until the piston hits the stop then take a reading from the degree wheel. Then turn the crank in the opposite direction till the piston hits the stop again and take another reading. Split the difference of the two readings and your there.
 
keith said:
A piston stop just threads into the spark plug hole and gives the piston something to touch against for a solid stop position. You turn the crank one direction until the piston hits the stop then take a reading from the degree wheel. Then turn the crank in the opposite direction till the piston hits the stop again and take another reading. Split the difference of the two readings and your there.
Click to expand...

Gotchya!! Thanks. Like the indicator but easier. Cool.

Thanks, opsled
 
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