Bent Connecting Rod

Stock is 77 dia x 53.6mm stroke

Athena is 83mm dia

Stroker crank is + 3 to stroke so 56.6

Did you do your math with +3/side making it 39.6?

I was hoping someone would do this soon... I've been seeing those cranks around and was really curious to see what they'd do. I'd say you would probably benefit considerably from cams at this stage.

Arkmage wrote:

Stock is 77 dia x 53.6mm stroke

Athena is 83mm dia

Stroker crank is + 3 to stroke so 56.6

Did you do your math with +3/side making it 39.6?

I was hoping someone would do this soon... I've been seeing those cranks around and was really curious to see what they'd do. I'd say you would probably benefit considerably from cams at this stage.

I used Pi/4 x bore² x stroke / 1000 Rechecked my math and it comes out to 306.24cc ;)

Agreed on the cams... problem is I couldn't find anyone making them for the WR. Hot Cams makes aftermarket cams for the YZ, but not the WR²

There are a few companies that will custom make them for you. Try calling hot cams, tell them what you have, and see if they can give you a quote.

One thing that I found interesting when checking the clearances was that with the stroker crank the quench ended up around .042". The stroker crank is +3mm, or about .120". I'm no expert on motorcycle engines, but I have quite a bit of experience with car engines. In a performance car engine build we always try to keep the quench are around .039". Doing so promotes better combustion and reduces the chance of detonation. The quench area on the stock engine must have been around .160"!!! Maybe there is something different about motorcycle engines, but I honestly can't imagine that being the case. In my mind, even though I'm adding compression with the increased stroke I'm getting the quench area closer to where it should have been all along. Thoughts?

P.S. Got the engine back in the frame over the weekend. Still have to reconnect all of the electrical connections, install radiator, etc... Hoping to get it fired up this coming weekend. Will keep everyone posted.

I wish I could offer some opinion on the quench question but it's out of my league. My degree is in chassis and suspension, I've pretty much exhausted what I've learned building motors and hanging out with the power train guys.

For me, as long as the valves and the pistons don't occupy the same space at the same time, the rest can be handled with tuning :)

Well, I finally got the bike running. Had a few problems on initial startup. Mostly worked through them now. Took the bike for a ride on/off road today. Logged about 145 miles on it. Overall the engine ran very well. I've got a lean condition off idle that is causing the engine to stall. I had this problem right after I put the Athena big bore kit in it. To fix the problem I had to add 10% fuel at 1,250 , 1,500 and 1,750 RPMs at 0% throttle. I may need to add more fuel due to the increased displacement from adding the stroker crank. There is also a possibility that the PCV unit is having some issues. I am getting intermittent errors from my laptop when I connect to the PVC. I tried a different USB cable with no luck. I also have a PCV on my 11' Ninja 1000, and I don't see these problems when connecting to the PCV on the Ninja using the same laptop/cables/usb port. So, that leads me to believe that the problem is with the PCV on the dirt bike. Lastly, I'm having some issues with the bike driving through the clutches. When I first got everything put backtogether, the bike would hardly move at all when in gear. I checked both adjustments on the clutch cable and moving then seemed to make no difference. I ended up taking the side cover off the engine to have a look at the clutches. The clutch assembly has 5 springs that provide the apply pressure to the clutches/plates. There is also a nut/shaft that runs through the center of the clutch that connects to the clutch push rod. This rod/bolt is what disengages the clutches when you pull in on the clutch lever. When I was reassembling the engine I put 10nm torque on this bolt as well as the 5 springs per my understand of the manual specifications. Turns out the clutch wasn't fully engaging with 10nm preload on the center bolt in the clutch pack. I backed the nut off this bolt compeltely and then just tightened it finger tight. It drove good for most of the day, but it was stil slipping some under WOT. Sooooo, a couple thoughts here. 1) The clutch linings could be bad from water getting in the engine, 2). The clutch springs could be bad, or 3). I may be exceeding the design limitations for the factory clutches.

I'm going to check around and see if a heavy clutch pack is available for the WRR. Alternatively, I may try to shim the stock springs to increase the effective spring rate. Not sure how thick the shims would need to be to increase the apply presure while still allowing enough air gap for disengagement. I would assume if I decide to shim the stock clutch springs that I would need to use machined washers/shims so that the spring rate remains even so as not to cause uneven pressure on the clutches/plates.

As for the power of the bike... I didn't run it super hard today, but I didn't baby it either. The power is VERY STRONG. Even with the clutches slipping a little I was able to run right beside my friends DRZ 400 up to 70 mph. I'm pretty sure once I get the tune sorted out and the clutch issues resolved my bike will have the edge. Not too shabby for a 306cc vs. 400cc. And I'm no light rider (205 with my gear). I couldn't audibly hear anyindication of detonation during today's ride. I'm going to pull the plug later this week and look at it under light/magnification for any signs of detonation. I've got quite a bit of experience reading plugs from racing cars most of my life. Usually detonation will result in "speckling" on the porcelan. In really bad cases it can cause the electrode to close up (sign this with nitrous engines before). I did notice that the bikes is pretty buzzy around 65 MPH, but not unbearable. It seems to smooth out around 70. I got it up to a true 84mph today, and it was still climbing.


Any way, just thought I would report back. Looks like the Athena 290cc Big Bore kit PLUS the Hot Rods 3mm stroker crank combination is a winner!

Do some searching on the clutch. The plates are the same as one of the yz bikes (same part number) and there was somebody who swapped to stouter springs because they didn't like the amount of slip in the stock setup. It's been done and there is info on it. Not sure if that was on this site or smj.

Did some research and calling around. Ended up talking to Kyle at Hinson clutches. I'm going to replace the factory frictions, plates and springs with Hinson's. The pressure plate, basket and innner hub all looked good. No gouging or other abnormal wear. Hinson also recommended not running synthetic oil. I've been running Yamalube semi-synthetic 10w-40 all along (2,900 miles). I'll post back after I get some seat time...

Well, just wanted to provide some closure to this thread. I replaced the stock cluthes/steels/springs with the Hinson kit. The directions that came with the Hinson kit said it was necessary to remove the "judder" spring. I have no idea what this is, where to find it or if this bike even has one. I checked the stack up height of the stock clutches/steels with a dial indicator. The Hinson kit includes more frictions/plates than the stock setup. I ended up having one friction and one steel left over from the Hinson kit. When I first installed the clutches and took the bike for a ride, the clutch was slipping really bad. I had the right amount of play in the cable, the correct ammount of preload on the spring pack. Upon closer examination I noticed that the pressure plate wasn't fully seating on the clutch pack. I disassembled everything and had a closer look at the frictions/plates. The directions stated that one of the frictions should be installed directly against the pressure plate. Sure enough, one of the frictions in the Hinson kit had a shorter lining than the others. Put this friction on last and everything is working like a champ! I understand what Hinson did with this kit, as I've dealt with multi-disk clutches in my race car. They've got a really nice clutch kit, IMO. It adds a ton of surface area (e.g. better clamping) than the stock setup. If anyone is driving through the stock clutches I think the Hinson kit is the way to go. No exotic materials (e.g. kevlar, carbon fiber), just a well thought out and manufactured kit. Thanks again to all those who helped me get this thing back on the road/dirt. This thing is running better than ever!

May I have your old crank? I want to experiment with it.

quick66 wrote:

One thing that I found interesting when checking the clearances was that with the stroker crank the quench ended up around .042".  The stroker crank is +3mm, or about .120".  I'm no expert on motorcycle engines, but I have quite a bit of experience with car engines.  In a performance car engine build we always try to keep the quench are around .039".  Doing so promotes better combustion and reduces the chance of detonation.  The quench area on the stock engine must have been around .160"!!!  Maybe there is something different about motorcycle engines, but I honestly can't imagine that being the case.  In my mind, even though I'm adding compression with the increased stroke I'm getting the quench area closer to where it should have been all along.  Thoughts?.

I'm getting ready to do a TR 306 kit so I was researching the builds, your comment about the quench distance. You do realized the HotRods connecting rod in your crank is 1.5mm shorter to compensate for the 3mm increase in stroke, right?

4play......0ld thread brother!

I understand, but there are not too many threads discussing stroker cranks & no on ever addressed his comments about the deck height.

4play wrote:

I understand, but there are not too many threads discussing stroker cranks & no on ever addressed his comments about the deck height.

+1