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Poor Boy Big Bore Kit

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davomoto
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Post by davomoto » Mon Oct 03, 2011 3:14 pm

Mark,

Per the Honda rate chart, you should be done by 9:42 pm . :-)

Davo

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flathead
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Location: Tennessee

Post by flathead » Mon Oct 03, 2011 9:59 pm

Davo,

Out and back in at 8:30. But no cigar. Slowed the leak to a drip, but still there. Anybody got experience with copper head gaskets? I used the OEM green orings this time but I think the leak is coming all the way around. I could have a cracked head. One thing I did remember was that I left the cylinders about .003 high like I usually do, Maybe the copper needs for the sleeves to be flush. I dont"t have a compression leak that I can tell so maybe thats it. I'm gonna retorque the head tomorrow and just run it a small bit at Barber. It's down to about 10 seconds right now and might get better with a retorque. I'm using a riveted cam chain and I don't have another masterlink anyway. If the retorque dosen't fix it I'm gonna go with a stock gasket. The pistons are below flush and the head backs the gasket up so I think it'll be OK. One good thing is, this thing runs as smooth as any 305 I've had before. I think it'd idle at about a hundred rpm and no vibration at rev. Running the Keyster CB kits with all Keyster brass , 135 mains and needles in the middle. A single CB750 coil, a CB750 condenser mounted under the points cover and 1 set of stock right points. Everytring set up per Ed's recipe minus the left points.

Mark

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davomoto
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Post by davomoto » Tue Oct 04, 2011 9:27 am

Nice work Mark! I've only used a copper head gasket on a big bore XL500, and it worked great! It may well be the raised liners that are causing the leak. Happy to hear that she runs well.

Davo

jerry
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Post by jerry » Tue Oct 04, 2011 3:53 pm

Dear Mark, Good on you regarding your project. I would be using 1mm cross section Viton "O" rings because you are using a .020" copper gasket. I only have the liners protruding .001" above the barrel. When I put my motors together using a copper gasket I apply a small amount of Honda crankcase gasket cement around the camshaft tunnel of the barrel. I also put a light coating of Loctite Never Seize on both sides of the copper gasket. It has always served me well. Just remember you may have deformed the copper gasket enough to cause cylinder sealing problems if you reduce the step between the liner and barrel face. All the best, Jerry

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flathead
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Post by flathead » Tue Oct 04, 2011 11:36 pm

Thanks for the info Jerry and Davo !!!!.
I think the .003 probably did me in as well as something that I knew about this twingle going in. I've got another one that I ride on the short track and we did discuss this before. The twingle is a huge pump in the crankcase so it creates a bunch of pressure that I didn't consider or really just plain forgot.

Not to be defeated, I started back at 5:30 this afternoon for another headgasket. The bore is out to 63.5 mm and the only fiber gaskets that I've got are stock ones that looks to be suitable for maybe 62mm. The pistons are not coming up into the head and actually are about .040 down at TDC. So I figure that I'm getting pretty good at this head gasket swapping and I've got 4 or 5 laying around so its worth a shot. Engine out in 30 minutes. When I went to take the head off I had torqued the thing so many times and up to around 30 ft/lb, that the sealing washers were sqeezed so tight around the studs that I had to split them with a chisel just to get the cover off. I checked the piston again at TDC and sure nuff it didn't project into the gasket surface. I put in a new cam chain this time with a clip type Masterlink. A whole lot easier to install. Engine back in and bolted down at 7:45. Hooked all the rest of the stuff and had it up and running at 8:10. Almost cried. Bad leak at right corner. It was running with a test tank so I could see what was going on. The leak was around the right front stud sealing washer. Thats when the light came on about the crankcase pressure. I pulled the capnut off and under the washer was a big old chisel mark where I had cut the sealing washers off. I took a scraper and smoothed the high spots down and filled the low spots with metal putty. Put on a new washer and re-torqued. I loosened up the oil filler and started it up. 1 kick, like every time before, and NO LEAK!!. I let it run about 15 min and shut it down to finish up all the loose ends everywhere else. Looks like I'm gonna have to put a crankcase breather on it. For right now I'm just gonna leave the filler loose. Everything else is pretty much buttoned up so maybe I'll get to take a ride tomorrow before we load up for Barber.

Mark

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davomoto
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Post by davomoto » Wed Oct 05, 2011 9:12 am

Excellent detective work! I've seen vents made into the oil fill hole, easy enough to do.

Davo
davomoto
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flathead
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Post by flathead » Sat Oct 15, 2011 3:31 pm

Made it back from Barber in one piece. Been recuperating for the past 5 days. I got to ride the bike a bit around the swap meet but not out on the road until this morning. Put in about 10 miles so far and am gonna have to do some carb tuning. It's running a little rich so I'm getting some plug fouling unless you ring it out good. Had it up to 45-50 for a shot or two. I really don't feel comfortable enough to put it through the mill yet to see what it'll really do. The oil leak has stopped and I don't think the stock head gasket's gonna be an issue. Here's a link to a video of the bike running.

http://s218.photobucket.com/albums/cc29 ... boy001.mp4

As you can see it really pisses off Trevor the Jack Russell.

Mark

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