Please add your worm to this can

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marshg246

marshg246

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I'm rebuilding a basket case that supposedly had the crank ready to install. Not trusting that I checked and the conrod nuts were finger tight as were the crankshaft studs. So, I took it all apart for inspection. The journals are beautiful and there are new shells. That's where the good stops. The conrod bolts are easy to put in and remove from both the conrods and bottom part - not used to that - I think someone reamed the holes. The bolts a snug but an easy slip fit. That's not the worse part.

The six studs are loose in both crank cheeks and the flywheel. I've seen the bottom and middle two be an easy slip fit but the top to are normally quite tight in the holes. I assume that between the bottom peg and the top two studs, the crank cheeks are located. I estimate that there is about 0.001" all around the studs.

Do you think the crank is usable? How about the rods?
 
Assuming that it is a pre-Mk3 crank, one solution to loose fasteners is to assemble the crank with enough fasteners (usually the bottom and middle ones), true it, tighten the fasteners enough to hold it securely, and ream the holes to fit 3/8" fasteners, using either the later Mk3 fasteners, or modern high strength aerospace fasteners, doing the top two first and reaming to a tight fit. The two middle fasteners can then be drilled (and reamed if desired) to a slightly looser fit. The crank can then be disassembled, and lower holes drilled/reamed, using the flywheel as a jig to drill the two halves separately. As you said, the two top fasteners and the bottom pin will locate the parts accurately, and the other 4 fasteners are for clamping force only.

This is a picture of a 750 crank modified in that way, back in the '70s.. In this case I used studs for the lower fasteners, and bolts for the other 4. I used NAS bolts and nuts, and AN studs (because that's what I could get). The flywheel is a replacement machined from a steel billet to the factory blueprints, but the same method would work just as well with a stock cast flywheel.

Please add your worm to this can


Ken
 
When I see fundamental understanding fails like you've described on these bolt/stud fits, that is always my signal to expect EVERYTHING is mucked up. What size do the journals measure?
 
marshg246 said:
Do you think the crank is usable? How about the rods?
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Good instinct, many in a hurry to get back on the road would find the answer to your question empirically in a fashion similar to Russian Roulette.

If there is no history on the rods I'd suggest they get binned. I have had a few go rounds with new OE rods and won't buy them any more, as much as I don't like the price point of Carrillo rods it is now the only maker I trust.

Jim Comstock, IIRC, wrote in this forum about going to 10 mm on the crank bolts, but check the crank for true first.

Best.
 
concours said:
When I see fundamental understanding fails like you've described on these bolt/stud fits, that is always my signal to expect EVERYTHING is mucked up. What size do the journals measure?
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Haven't done that yet - but will. I'm checking everything. For instance, a set of barrels properly bored to a new set of pistons, but powder coated and the powder coat is flaking off and the same guy who powder coated the barrels used duct tape to affix the tappets to a piece of cardboard so he could mark their location - what a mess!
 
RoadScholar said:
Good instinct, many in a hurry to get back on the road would find the answer to your question empirically in a fashion similar to Russian Roulette.

If there is no history on the rods I'd suggest they get binned. I have had a few go rounds with new OE rods and won't buy them any more, as much as I don't like the price point of Carrillo rods it is now the only maker I trust.

Jim Comstock, IIRC, wrote in this forum about going to 10 mm on the crank bolts, but check the crank for true first.

Best.
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Weighing the cost of the things I would need to be sure the crank is true to just using a crank I was saving for another project. Did a little more checking, I could easily ream to 8mm and try to find acceptable bolts or studs, or go further to 3/8" and get the studs from AN. Good ideas once I know the crank is true. Not hard with a surface plate and height micrometer - neither of which I have. Will discard the rods, tried multiple sets of ne bolts, all slip in too easily. What a waste!

I've read a few threads about early and later 750 cranks and was left confused. This bike is a late 73 750. One crank I have is an early 71 750 and one is an early 72 750 from a Combat engine and one is from a 73 850. Have to figure out which are compatible.
 
marshg246 said:
I'm rebuilding a basket case that supposedly had the crank ready to install. Not trusting that I checked and the conrod nuts were finger tight as were the crankshaft studs. So, I took it all apart for inspection. The journals are beautiful and there are new shells. That's where the good stops. The conrod bolts are easy to put in and remove from both the conrods and bottom part - not used to that - I think someone reamed the holes. The bolts a snug but an easy slip fit. That's not the worse part.

The six studs are loose in both crank cheeks and the flywheel. I've seen the bottom and middle two be an easy slip fit but the top to are normally quite tight in the holes. I assume that between the bottom peg and the top two studs, the crank cheeks are located. I estimate that there is about 0.001" all around the studs.

Do you think the crank is usable? How about the rods?
Click to expand...
Ken's suggest will fix the crankshaft for you. Perhaps it would be worth sending a sample rod bolt to ARP or similar vendor. Ask if there is a similar bolt of slightly larger diameter? I'm thinking of a metric engine with 10mm bolts. Or if they could make oversize bolts for you?

ARP Racing Products
 
chaztuna said:
Ken's suggest will fix the crankshaft for you. Perhaps it would be worth sending a sample rod bolt to ARP or similar vendor. Ask if there is a similar bolt of slightly larger diameter? I'm thinking of a metric engine with 10mm bolts. Or if they could make oversize bolts for you?

ARP Racing Products
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Actually, I think 8mm bolts are just enough bigger, 5/16=.3125, 8mm=.3150 but that's does not fix the truing issue - I cannot be sure they were drilled with the crank properly together. I like the idea of using 850 top bolts - I don't think the others matter as much. For now, I'm just going to use another crank and I'll fix this one once I have time.

I did figure out that a surface plate and four precision parallels of the right sizes would work to true it.
 
marshg246 said:
Actually, I think 8mm bolts are just enough bigger, 5/16=.3125, 8mm=.3150 but that's does not fix the truing issue - I cannot be sure they were drilled with the crank properly together. I like the idea of using 850 top bolts - I don't think the others matter as much. For now, I'm just going to use another crank and I'll fix this one once I have time.

I did figure out that a surface plate and four precision parallels of the right sizes would work to true it.
Click to expand...
Greg, As a general rule, a drill or reamer will follow the center of an already drilled hole. It would require a truly talented idiot to mess that up! But as you say, better to check and know.

One repeatable test is worth 1,000 expert opinions - Bob Nucholls author of the AeroElectric Connection

What are your plans for the connecting rods??
 
chaztuna said:
Greg, As a general rule, a drill or reamer will follow the center of an already drilled hole. It would require a truly talented idiot to mess that up! But as you say, better to check and know.

One repeatable test is worth 1,000 expert opinions - Bob Nucholls author of the AeroElectric Connection

What are your plans for the connecting rods??
Click to expand...
I agree, especially with a reamer, but only if he crank were together when reamed and I doubt that. Since the bottom holes are equally loose and since the holes are not perfectly round, I'm fairly sure a drill was used, most likely by hand, while the crank was apart.

More study on the rods. I'll probably use the set that's on the crank I'll use and worry about the rods later too. Like an idiot I made too my promises for the end of Spring so I need to get these bikes done and I don't allow myself to take short cuts or chances so need to keep from getting sidetracked.
 
Best laid plans -- often fail! I had a fifthly engine that supposedly was in good shape just dirty (glad I didn't sell it to Coolhands to fix his problem). Once I got it apart I was happy with the connecting rods and the crank journals looked great. The drive side crank outside the case had surface rust but no big deal. It had a recent bore and 0.040" over pistons but a large chunk of fin missing. Then I cleaned the crap off the other end of the crank and there is a chunk missing :mad: So, this crank is junk - oil won't seal. Probably a welding expert with a lathe could fix it, but I certainly can't. I've got two more cranks - I hope one of them is 750 and good.
 
marshg246 said:
Best laid plans -- often fail! I had a fifthly engine that supposedly was in good shape just dirty (glad I didn't sell it to Coolhands to fix his problem). Once I got it apart I was happy with the connecting rods and the crank journals looked great. The drive side crank outside the case had surface rust but no big deal. It had a recent bore and 0.040" over pistons but a large chunk of fin missing. Then I cleaned the crap off the other end of the crank and there is a chunk missing :mad: So, this crank is junk - oil won't seal. Probably a welding expert with a lathe could fix it, but I certainly can't. I've got two more cranks - I hope one of them is 750 and good.
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May be a sleeve could help ( Speedi-sleeve, or custom one with appropriate larger ID oil timing seal ...?)
 
marshg246 said:
snipped Then I cleaned the crap off the other end of the crank and there is a chunk missing snipped
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Greg,
Any chance of posting or linking a photo of the damaged area. I know of a shop that does major crankshaft repair.
 
chaztuna said:
Greg,
Any chance of posting or linking a photo of the damaged area. I know of a shop that does major crankshaft repair.
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I sent it off with my stepson. He as a machine shop friend that might be able to fix it - he'll at least say if he feels OK about it. He did fix a BSA B25 crank for me, but they are so sloppy that I probably could have done that one with a stick welder and file!
 
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OK, spare crank is fine - it's apart and clean - just waiting for my AN order to arrive as I'm out of crank studs and nut kits.

Now I need to figure out how to get the powder coat off the barrels. It's flaking off on its own but just enough to make the barrel ugly. It was applied very thick and probably the barrels were oily. On small parts I simply heat to about 500F, scrape, and then blast the thin remaining coating. I doubt that will work on barrels. Anyone removed powder coat from barrels?
 
marshg246 said:
OK, spare crank is fine - it's apart and clean - just waiting for my AN order to arrive as I'm out of crank studs and nut kits.

Now I need to figure out how to get the powder coat off the barrels. It's flaking off on its own but just enough to make the barrel ugly. It was applied very thick and probably the barrels were oily. On small parts I simply heat to about 500F, scrape, and then blast the thin remaining coating. I doubt that will work on barrels. Anyone removed powder coat from barrels?
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I have used Aircraft Paint Remover to remove powder coating. Not from barrels, but I'm thinking should apply there as well. Wash & Blast after.
 
NickZ said:
I have used Aircraft Paint Remover to remove powder coating. Not from barrels, but I'm thinking should apply there as well. Wash & Blast after.
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Greg, Make sure whatever product you buy, has Methylene chloride as an active ingredient. This chemical has been removed from many products in the past 2 years. The substitute chemicals are all but worthless on Powder Coat and Polyurethane paints. Methylene chloride is the active chemical on "real" carburetor cleaner. To my knowledge, only Zep Products still has it as an active ingredient. [ I have a 4 gallon pail of it in my workshop]
Since it's flaking off, maybe try a pressure washer???
 
chaztuna said:
Greg, Make sure whatever product you buy, has Methylene chloride as an active ingredient. This chemical has been removed from many products in the past 2 years. The substitute chemicals are all but worthless on Powder Coat and Polyurethane paints. Methylene chloride is the active chemical on "real" carburetor cleaner. To my knowledge, only Zep Products still has it as an active ingredient. [ I have a 4 gallon pail of it in my workshop]
Since it's flaking off, maybe try a pressure washer???
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Here's the interesting thing. At least in VA, I can find no Methylene Chloride containing paint stripper, but up to about a month ago you could order a gallon of Methylene Chloride from Amazon - I did. I wish I had ordered more. I will try the pressure washer idea - thanks.
 
chaztuna said:
snipped Methylene chloride is the active chemical on "real" carburetor cleaner. To my knowledge, only Zep Products still has it as an active ingredient. [ I have a 4 gallon pail of it in my workshop]
snipped
Click to expand...
I guess I was a bit vague with the above statement. Zep Products makes carburetor cleaner with Methylene Chloride in it. Many times I'vd dunked parts into my carb cleaner pail to strip off paint. Works great.
 
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