Well, my 340 kit is installed and I took the bike for its first run up & down my street an hour ago. A few tense moments along the way but by taking breaks and working through the rough parts it all turned out great.

I got a 340 kit from Bill Blue. He orders the same piston and gaskets as Thumper racing used to do (still do?).
BIG BOY!!!

Sent him my 250 cyl and got back a beautifully sleeved and honed work of art. Even crosshatching along every square mm of the bore. Great work! I carried it around with me in my house for a while like a new toy, I was so psyched about this new cylinder...

Okay, so here the new cylinder is installed. Thoughts: First thing I did was install one of the circlips. (Right side one) Practice on your old piston a few times, they're a bitch.. Then I installed the rings onto the piston with my fingers - I followed the diagram that came from Wiseco. No sweat. I lightly oiled the bore and then -at my kitchen table, in good light, carefully - installed the piston into the bottom of the cylinder. No ring compressor, just squeezing the rings one at a time. No sweat! I made sure it was sticking out low enough so the wristpin could be slid in when the time came. Note that there are two dowel pins registering the cylinder to the case. I sent one to BB, so I had to pick one up from Kawi. Luckily they had em in stock - only a slight delay. Cleaned the surfaces, put the gasket on, kept track of the timing chain so I wouldn't lose it, and carefully mated the con rod and piston. The wrist pin slipped through with laser like precision - amazing. The second circlip went on very easily. I was done!! breathe a sigh of relief.. until I realized that the rear timing chain guide had to be fitted through the cylinder which I forgot to do! And the things do not bend! ##(*$ )#(*$)9 &)#($!!!! Had to take the circlip/wristpin out and redo the whole process. By taking out the circlip I scratched the bore that the wristpin slides in so I had to force it out with a big screwdriver. Not a fun thing to do, I was beginning to hate life at that point. And then of course, the super precision fit was ruined, the wristpin would not slide in easily, it was very tight. So I cursed. and then went back to the kitchen table to see what I had done. Using an exacto knife, I was able to carefully shave down the few offending lumps and restore the smooth fit that the wristpin needs. I was back in business, and got the cylinder on in no time THIS TIME REMEMBERING TO SET THE CYLINDER DOWN OVER THE REAR CHAIN GUIDE!!!
-- and it was done --

Head gasket was next, then the head, torquing it down to specs. Don't forget the two locating dowels. No gasket sealer was used, my cylinder had a very small ridge in the top of the liner that presses into the headgasket making a solid seal. Bill Blue craftsman's touch, very nice. The front chain guide gave me a headache, its not really mentioned how to get it in correctly in the manuals, and to confuse the situation even more, the exploded view shows a bolt and washer holding it in.... So I fiddled with it and the cam wouldn't seat in its ways, fiddled with it some more.. It comes down to having to push it very firmly down into the case. Its a tight squeeze fit, but it should end up lower than the rear guide, and then your cams will sit on their bearings and the chain can then be set over to get the timing ritght. piece of cake once the damn guide is in place correctly. Note, this how the cams are at TDC.

Bolting down the cam "girdle" is next. Well, the damn thing wouldn't get down into place.. I thought it was the locating dowels being tight, but I knew not to force it. After jiggling things around a bit, I noticed the intake cam was not seated properly in its bearing, it was resting on its bucket which was sitting about a sixteenth higher than the other. I lifted the bucket and saw the shim off its perch. I set it down correctly and the bucket went in and the cam sat flat and the girdle slid right into place. Sweet! What happened was that during the teardown process, two of the valve spring buckets fell out of the head, and when I put them back, apparently one of the shims slid out of place. (DONT FLIP YOUR HEAD OVER WITHOUT HOLDING THE BUCKETS DOWN!)
Torquing it was kind of iffy with a 1/2 drive beam wrench, but I got it as even as I could.

From here on all the critical things are over. Hook up the oil line and radiator connections. Install the two chain tensioners.. I checked valve clearance once again, oiled up the cams and spun the engine with a wrench a few times to make sure everything was running smoothly. And it was. I used red permatex (hi temp) gasket sealer on the head cover gasket, and got a nice even squeeze out all around. The manual only says to put in on the half round sections, but there was sealer all around it from the factory so I did the same. Gave it overnight to set up. Filled with oil and antifreeze. Put carb on (MAJOR BITCH FCR35) exhaust back on (NEED NEW COPPER GASKET!) fan on, Coil on, tank, all the bull ****. Getting nervous for that first crank.. Cranked it a few times w/ no fuel or sparkplug so the oil could pressurize a bit..
Added fuel and sparkplug, but it wouldn't run! Turns out my carb idle was set all the way low so I adjusted it and it settled into idle! Installed my Utah skid plate and Ebay foot pegs... She sounds like she's runnig rich, (stumbling, popping) I may lower the needle a notch or two.. Ran fine though besides the carb tuning, need to get a few more heat cycles in on it before I really lay into it of course.

Happy me!

~Steve

 

Great Job! Nice pics too! those extra cc's are cool!

 

Congratulations! Thanks for posting up the pics. I think a big bore is in my future someday.

 

I can say no other mod made the change that the big bore made. just upgrading to the 300 makes you sit a little closer to the tank than I used to.

 

Nice write up & pics!

 

Yeah, the bike is finally what I want it to be.. Once the engine is broken in and the carb is tuned a little better, I have some serious "barely DOT" tires to go on and I think it'll be perfect! I also have a Terrycable hotstart to put on once I have the carb off again for tuning. Only thing after that would be to get some low profile blinkers. .

Anyone out there on the fence about doing this themselves, don't be afraid, its easy!! Just take it slow and one step at a time. Scour the boards for answers.

~Steve

 

Awesome! Not something I will ever do, unless my engine blows up or something. Great pictures and writeup.

 

Nice write-up. Not everyone will share their 'oopsies,' but it's worth it's weight in gold for lessons learned Thanks!

I notice a pretty pronounced dish in the top of that piston made for Thumper Racing, which makes sense to me now. I believe they advertised a 10.5:1 compression ratio for their kit which is about .5 lower than stock. You should be able to run any grade of gas without worry. Nice, torquey, reliable power... good stuff!!

Most of the 331 kits offered will boost the compression ratio to at least 12.0:1because they don't compensate for the increased displacment by increasing combustion chamber volume like Thumper did by using that dished piston.

 

Yeah, its curious the dished piston. I read about the 10.5:1 CR, and then I got an email from Bill Blue stating the CR of the 340 as 12:1 (compared to his 351 at 12.5:1) So maybe Bill shaved the cylinder a bit? Or maybe it is still 10.5:1 Ill email him, see what he says. I'd like to know for sure/. is there a way to measure (leakdown test type of thing..?)
~Steve

 

There's a formula that needs data like bore, stroke, distance from top of piston at TDC to top of cylinder, combustion chamber volume (measured with liquid)...you also need to measure the volume of the dish at the top of the cylinder and there is something about distance from the top piston ring to the top of the piston....so no, there's no way to do it without taking the whole thing apart.

Unless Bill altered Thumper Racing's piston, it's 10.5:1. I remember them talking about how they experimented with different compression ratios and found that this engine 'liked' 10.5:1 best. Can't dig-up the original data though because their website is gone.

I think Bill probably knows the exact compression ratio of his 351 kit because that piston was specially made for him, so he's got all the specs. For the 340, I think he's just plugging in the smaller bore of that piston into the standard formula, but leaving the rest of the numbers the same, which would give him that result.