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Author Topic: 535 piston clearance  (Read 3180 times)

dogbone

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535 piston clearance
« on: January 25, 2008, 05:04:45 PM »
Wondering what clearance 's anyone  are using on the forged 535 8.5:1 piston
Factory std slug is .04   I have honed to .07  Too tight ?
99 Enfield Bullet 535
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cyrusb

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Re: 535 piston clearance
« Reply #1 on: January 25, 2008, 05:56:40 PM »
I'm assuming that you mean .004 inches? Wouldn't .007 be too loose? Anyway, how do the pistons compare weight wise?  If you liked the balance of the original motor you might want to keep the weights close.

dogbone

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Re: 535 piston clearance
« Reply #2 on: January 28, 2008, 08:24:06 PM »
cyrusb  The 535 piston is a big old slug of aluminum. At least 25% heavier than the oem, the skirt is longer also. I expected more expansion, and I also run the crap out of my engine.
PS is that a schnauzer?
99 Enfield Bullet 535
a man isn't drunk,if he can lie on the floor without hanging on

cyrusb

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Re: 535 piston clearance
« Reply #3 on: January 29, 2008, 05:28:34 PM »
Yeah, he's a schnauzer, best dog we have ever had. I guess if your going to
" get it hot" the more clearance the merrier. You can expect some slap when its cold, kinda like a race engine. I wonder if you'll even notice the extra noise with these engines, It should blend in with the symphony. I would be leery putting a much heavier piston in, but if its proven, and I hope it is after all these years, its probably fine. Have you seen any of these motors bottom ends out of the bike? I'm still mystified by the floating bushing. In 40 years I have never seen an engine that used it. Before I became aware of it I believe it was called a "spun bearing". Why 2 bearing surfaces on 1 pin? Even my old triumphs had conventional rod bearings. How can any of the two bearings be an effective pump itself when its vented to the other bearing?Details are sketchy, but I think Ive seen four holes in the bushing itself allowing oil to get to both sides. But this also will vent the high pressure generated on one surface to vent to the other. Hey but it works, and for many miles, so what the hell.

fredgold52

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Re: 535 piston clearance
« Reply #4 on: January 29, 2008, 05:40:06 PM »
I think I would have been inclined to go with the standard .004" clearance.  My experience with other bore enlargement modifications has shown me that .004 is good for most applications.  It's common for me to take a 150cc two stroke engine up to a 177cc and maintain the .004.

The only way (IMO) the piston will expand past the .004 and seize up is if; 1. you're running the crap out of it before it's broken in, 2.  The jetting is way lean, and 3.  the timing is off in 'pingville' someplace. 

At this point though, you have honed another .003 out of the bore.  Might as well put it together and run it.

With the 8:1 compression piston and the larger bore producing a more powerful 'thump', I believe I'd be looking to add the high powered oil pump to this engine.  With adequate oil flow, the bearing should stand up to the new piston unless you destroy it with RPM's.

Good luck with this project.  I hope it works out well for you.

Fred
2006 '65' and a 200cc Stella, Indian all the way

dogbone

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Re: 535 piston clearance
« Reply #5 on: January 29, 2008, 08:59:35 PM »
cyrusb   yea I have 2 schnauzers, don't need a doorbell   ::)
I always warm my engines completely b-4 running them hard.  I was trying to compensate for the extra aluminum expansion .
The plain end bearing reminds me of my Packard engine Gravley. same concept, but a larger crank pin.
99 Enfield Bullet 535
a man isn't drunk,if he can lie on the floor without hanging on

cochi

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Re: 535 piston clearance
« Reply #6 on: January 30, 2008, 09:30:59 PM »
Cyrusb, regarding the floating bushing found in the Bullet  motor. I can't think of any automotive or bike application. However, if my memory serves me these bushings are used in radial aircraft engines. I think both Pratt @ Whitney and Wright radials use them on their big ends. Years ago,in a previous life,I had the pleasure of tinkering on a couple of Pratt @ Whitney Wasps. These are incredible motors. I think the original designer of the Bullet motor (can't recall his name) took some cues from the aircraft industry. Cocchi

cyrusb

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Re: 535 piston clearance
« Reply #7 on: January 30, 2008, 09:45:36 PM »
Ah yes, the slave rods, thats right. And with dogbones Gravely tractor that makes two. I'm slowly beginning to like the "odd rod".

SRL790

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Re: 535 piston clearance
« Reply #8 on: February 02, 2008, 02:20:55 AM »
When I rebuilt my 350 I replaced the floating bush with a roller bearing.  I think I got it from Hitchcock"s.  It came as a kit complete with crank pin.

When I stripped my engine at 38,980 miles the only part that had actually failed was the floating bush, although this was more likely due to poor maintenance than anything else.

Whether or not it has any real advantage over the floating bush l don't really know but it's something you might consider for a "high" performance engine.
Andy Wiltshire
54 350 Bullet, 62 Jaguar MK II, 68 BSA Spitfire, 69 BSA Starfire
70 Bonneville, 71 Bonneville, 71 BSA B25T, 74 Jensen Healey
74 Honda XR75, 81 Yamaha MX80, 82 Suzuki GS1100G

birdmove

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Re: 535 piston clearance
« Reply #9 on: February 02, 2008, 04:06:14 AM »
    Andy, how about you share with us how we can get 40,000 out of our Bullets?? You must be doing something very right!

    Jon in Puyallup
    2007 500 Classic with 206 miles and counting........
Jon in Keaau, Hawaii

SRL790

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Re: 535 piston clearance
« Reply #10 on: February 02, 2008, 04:58:44 AM »
Jon,

I wish I could claim that it was due to my knowledge, wisdom and excellent riding skills, but the truth is that when I bought the bike (in 1983) it already had 35,000 miles on it.

Other than the disintegrating floating bush the only other engine problems were just extreme wear in the cylinder, worn valve guides, etc.  I was quite suprised to find that it still had a standard piston and had apparently never been apart before.

I did find a cracked gear in the transmission that I had to replace. (Thank you Beano Rodi)!

So far I have a little over 4,000 miles on the rebuild and it seems to be doing fine after a few teething problems.  If I get to 80,000 miles then maybe I'm onto something and I'll let you all know. ;D

Andy Wiltshire
54 350 Bullet, 62 Jaguar MK II, 68 BSA Spitfire, 69 BSA Starfire
70 Bonneville, 71 Bonneville, 71 BSA B25T, 74 Jensen Healey
74 Honda XR75, 81 Yamaha MX80, 82 Suzuki GS1100G

cyrusb

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Re: 535 piston clearance
« Reply #11 on: February 02, 2008, 08:59:39 PM »
Jon,

I wish I could claim that it was due to my knowledge, wisdom and excellent riding skills, but the truth is that when I bought the bike (in 1983) it already had 35,000 miles on it.

The previous owners must have really understood what they had there. I believe with a light right wrist those milage figures can be achieved by most riders. I think big bore kits really stress the whole shebang. If what I read is correct, the 500 are really bored out 350s. Thats quite an increase ,percentage wise, and it really sucks up the safety factor in the original 350 design. Much beyond that, and your in the "granny on dexis" mode.