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noexit
Samba Member
Joined: September 18, 2006
Posts: 329
Location: Tacoma, WA
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 Posted: Tue Aug 21, 2007 7:48 pm Post subject: Crank bearings |
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I'm restoring a 1969 Honda CL350 right now, and looking at this beefy little engine got me thinking, why can't VW engines have roller bearings on the crank?
The 350 twin I've got torn apart has 4 big roller bearings on the crank. The engine is practically bullet proof, redlining at 11,500 rpm, and it could go to 14,000 or higher if I put needle bearings on the cam shaft.
I've had crank break in half because of a poor rebuild by the PO, ruining a case. Couldn't a VW engine be built with roller bearings? It seems like this would both increase the life and power of the engines by quite a lot. |
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miniman82
Samba Swamp Donkey
Joined: March 22, 2005
Posts: 9515
Location: Southern Maryland
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| Posted: Tue Aug 21, 2007 8:04 pm Post subject: |
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Ummm, you're about 40 years too late there boss. Do a search for SPG cranks....
_________________
Build thread: http://www.thesamba.com/vw/forum/viewtopic.php?t=212747
| Glenn wrote: |
| satterley_sr wrote: |
I just wanted to bitch but I'm getting no sympathy. |
Welcome to the Samba. |
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Blaubus
Samba Member
Joined: October 25, 2003
Posts: 5153
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| Posted: Tue Aug 21, 2007 8:09 pm Post subject: |
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| It seems like this would both increase the life and power of the engines by quite a lot. |
well maybe, maybe not. armchair hypotheses dont always pan out in reality.
i should also have six spark plugs per cylinder. by my calculations that should give me 75 mpg 
rollers on the motorbike was probably a high temp choice for that type of engine. probably wasnt intended as a low friction choice
BTW the crank bearings cant make all parts of the engine bulletproof. typically the exhaust valves are the weak link on any aircooled engine |
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SRP1
Samba Member
Joined: January 06, 2007
Posts: 4340
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| Posted: Tue Aug 21, 2007 9:15 pm Post subject: |
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| miniman82 wrote: |
| Ummm, you're about 40 years too late there boss. Do a search for SPG cranks.... |
No not really. The SPG cranks only used roller bearings on the rod bearings not on the mains. I don't know of anyone who has done a true full roller crank. |
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noexit
Samba Member
Joined: September 18, 2006
Posts: 329
Location: Tacoma, WA
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| Posted: Tue Aug 21, 2007 9:55 pm Post subject: |
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| miniman82 wrote: |
| Ummm, you're about 40 years too late there boss. Do a search for SPG cranks.... |
Well, I wasn't around 40 years ago. But, it seems that Porche had good luck with roller cranks. If I'm not mistaken, SPG cranks twisted when you dropped the clutch because they weren't pinned together.
| dansvans wrote: |
rollers on the motorbike was probably a high temp choice for that type of engine. probably wasnt intended as a low friction choice
BTW the crank bearings cant make all parts of the engine bulletproof. typically the exhaust valves are the weak link on any aircooled engine |
I'm pretty sure it was intended to be low friction. Friction=heat, and my aircooled 350 runs just a cool, if not cooler than my VW 1600. Without roller bearings, it's doubtful that the honda would be able to redline as high. If I were to make a higher performance engine, of corse I'd also have to replace the stock valves and springs, but that's true on any engine, not just aircooled.
I guess I just don't get why the materials are so... soft? that a bearing would destroy itself so throughly that it could take a crank and case with it. No chance of salvage. After 70 or so years of this engine, there must be a way to improve on this design. Maybe the PO used crappy bearings, maybe he did something else wrong. It just doesn't seem like that sort of thing happens often on other engines. |
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