Another 310cc build

The title says it all, I'm in the process of rebuilding my engine as it has thumped its last breath after 5500mi. Now I will admit, I've put a lot of money into upgrading the bike, but my bike gets USED. I am not nice to this little turd of a motorcycle and up until now I had no problems with it.


This statement is for those who insist on telling me I should buy a real bike. I will be purchasing another bike, most likely a KTM 350EXC and this bike will become my motard for commuting so it's not a loss in my eyes. I've budgeted the build costs and it will be about $3000. Considering what I've spent on my 2 vintage VW's, this is almost a pocket change build so money isn't my concern. Having fun with the experience is the focus of this project. If you've searched on youtube for 310 builds then you probably know what I'll be doing to this bike.

A little back story:

I purchased an 08 WR250R back in May of 2017 for the sum of $2850. The bike already had Pirelli trials tires, Flatland skidplate and radiator guard, tail delete, and an aftermarket shifter lever. I did a bunch of work to the bike over the months to make it more enjoyable on the trails and racked up about 1000mi. of single and double track trails here in the Pacific Northwest. About 3 months ago I noticed my bike was having more and more trouble starting when it was cold. Didn't think much of it as it always started and got me through the trails just fine. It finally got to the point that it wouldn't start unless I did the following. Attempt to start the bike, disconnect the fuel pump plug, turn over the engine until it sounded like it wanted to start (excess fuel in intake tract) and while still cranking I would plug in the fuel pump. The bike would start slowly and restart without issue once it was warm. The only thing I didn't check was the compression because my compression tester didn't have a fitting small enough to fit the spark plug hole. And considering I took it back to the dyno to be retuned to work with the airbox mods and the tuner said the fuel controller was working fine and making 27.70 RWHP I was convinced the compression wasn't suspect. The bike made 27.70hp at the wheel on a big ol' heavy Shinko 505 cheater tire and 13/48 gearing. After chasing everything I could think of to include replacing the ECU with a good used item. I finally deciding to throw in the towel and take it to the local stealership and shortly after I found out what was wrong. Minimum compression values are 121psi, mine was 60psi!!!! The mechanic was surprised I was able to ride it let alone get it started.  And even more to his surprise I took the compression issue as great news.

Mods done so far:

Shinko 505 cheater rear tire
Shinko 546 front 90/100/21
F&R Tubliss tire inserts
Supersprox 13/48 sprockets
WR450F rear brake assembly
WR450F 270mm front rotor upgrade
Galfer stainless braided brake lines
EBC Sintered rear pads
EBC Red front pads
Ox Brake LHRB for WR450F
Zeta brake lever
Righteous Stunt Cycle clutch lever
Pro Taper Charmicheal bars
HDB bark busters
Scotts under handlebar steering damper
Double Take collapsible mirror.
IMS 3 gal. gas tank
aftermarket replacement fuel pump insert
Full FMF Q4 exhaust with power bomb header
Power commander fuel controller tuned by Nels 2 wheel dyno service
Airbox mods w/ No toil airfilter
Intake silencer delete
AIS smog delete w/ 12 o'clock labs thingy to make the CE light go away
12 o'clock labs speedo healer
Rekluse EXP 3.0 auto clutch
Baja Designs turn signals in rear
Rear fender delete & license plate relocation
Seat Concepts shaved seat (bike is still tall for 5'10", lol)
All new OEM body panels from Partzilla
SR moto retro decals
Pivot Pegs
Home made Steg Pegz

***As soon as I figure out how to post pics I'll do so.***

So where I'm at now:

I've been looking for another project and was intrigued with the idea of taking on a bike project. So far I've purchased the 290 Athena kit and the Hotrods +3mm stroker crank, and Tusk 10% stiffer clutch springs. I contacted Lindsay Machine Racing (LMR) about doing the throttle body 2mm overbore and a trail focused port and polish on the head. They told me I need to send in my camshafts with the head which means I need to get the camshafts sent out to WebCam first for the hardweld and regrind (3wk turn around). LMR also stated the work to the TB and head would take about a month to complete. Once I receive the piston kit and stroker crank they will be sent to Thumper Racing for balancing.

To be continued...

Should be a sweet build! Looking forward to updates.

Looking forward to hearing how the build goes!

Thanks, I'm looking forward to seeing how much of an improvement I can manage over the tired engine I've been running. I just received the HotRods +3mm crankshaft. Almost laughed at how small it is compared to the cranks for my other engine projects.

Finally figured out how to upload pics, so here are a few.

How I bought it:

How it looked after 3mo.:

How it looks now:


The pathetically tiny +3mm HotRods Stroker crankshaft


Talk about bad timing!!! I purchased a spare cylinder head, camshafts, and throttle body in order to get all the machine work done while I was riding the bike. Unfortunately, now I have a dead motor and no longer need these parts. Hopefully, I can put them back on ebay and recoup my investment. On another note, I just checked the parcel tracking and it appears my 290 Athena kit will be here sometime today or tomorrow. It will be a paycheck or two before I can send all the parts out for machining. Gotta be an adult every now and then and pay the bills, lol.

More goodies came in the mail yesterday. The Athena 290 kit is here and now I'll be packing it up and getting ready to ship it and the crank out to Thumper Racing. I heard the casting of the cylinder left a bit to be desired in terms of quality, but I have to disagree. The cylinder is very clean, no ugly casting lines or sloppy moulding features evident of a rushed product. Compared to the aftermarket VW crankcases I'm using this thing is solid gold in terms of casting quality. The piston is a nice piece with graphite coating on the skirts. The design is one that doesn't leave room for removing additional material. Meaning I believe it's as light as it's going to get without going to a hyper exotic material and super expensive machining. I do have concerns about the single compression ring, but it wasn't a surprise when it arrived as I did some reading before purchasing. I'll just treat this as a replacement item much like what you'd find on a true enduro/race bike. Periodic inspection and replacement when needed. Truth is, if you want stock reliability and maintenance, leave it stock, lol. Much to my surpise, I thought I purchased the kit without the FI add-on as it's of no use to me, but the price was the lowest I found so I guess it doesn't matter.

Following your build. Love the pics so far.

Thanks, I'm getting impatient with the fact that I can't just buy and do everything in one shot and start building the next day, lol. I just keep telling myself that missing the riding season will be worth it when it's done. I'm going to pack the crank and piston and try to send them out by Monday. But the head and throttle body will probably have to wait at least another 2wks before I can send them out.

Just finished a 13hr night shift and was happy to see a few goodies in the mailbox. I'm not normally the type that gets into the blingy side of the motorsports industry, but when the aftermarket part is cheaper than the OEM I know which one I'm buying. When I upgraded to the 270mm front brake kit I found out that one of the screws in my front brake reservior was too tight and I stripped it. In order to remove it I cut a slot in the head of the screw with a dremel which also meant that I had to cut a slot in the cover as well. Being me I can't leave things looking janky so I purchased a Works Connection reservoir cover. My only gripe is I'd rather have black and that isn't an option for this bike. The Tusk clutch springs may not have been necessary, but I feel the hp/torque numbers will be enough to either reach the absolute limits of the stock springs or slightly exceed them. So for less than $20 it didn't seem like a bad upgrade for 10% stiffer springs. And if the pull at the lever is too much, then thank goodness for a rekluse, lol.

Where did you get your big bore kit and how much?

I purchased it for $721 off of Ebay, but the invoice said Tucker Rocky which is a distribution company from what I can tell. Other than machining services, all of my purchases will be Ebay. It seems that Ebay is a more competitive sales platform and retailers are a bit better with prices. Just pay attention to what they're charging for shipping otherwise you'll be paying .99 for the part and $800 in shipping, lol.

So here is the parts breakdown for this build, I'm sure many people are wondering what it costs and where the money is going. I'll be updating this post as the total parts costs are finalized (including shipping)

310cc Big Bore Stroker Projected costs:

HotRods +3mm crank $332.00
Athena 290cc Bigbore Piston kit $721.00
Head, Camshafts, and Throttle Body $571.00 (purchased, but will most likely resell)
Tusk 10% heavier clutch springs $16.00
Krieg Cam Chain Tensioner = $40.20
Remapping w/ Nels $110.00
LMR Cylinder Head p&p w/ good valvetrain $500.00
LMR Throttlebody +2mm Overbore $300.00
Thumper Racing Crank Balancing (with heavy metal and shipping both ways) $400.00
WEB Cam Hardweld & Regrind Camshafts $573.00
**Athena Complete Gasket Kit = $70.00
Total: TBD     Purchased: $1509.2

**May not need**

Thanks for sharing pricing info. That price for the big bore kit is the best that I’ve been able to find as well.

Another long shift rewarded by goodies in the mail. This morning I received the Krieg Cam Chain Tensioner. Its a very nicely made piece with the all business look of aluminum and shiny hardware. It's nice to see that all the points of concern were addressed such as an o-ring under the locking nut to prevent oil weeping through the tensioner bolt threads.



On another note, according to the mail tracking number my stroker crank/rod assembly and 290 piston have arrived at Thumper Racing for rebalancing. I was informed TR is understaffed at the moment so it may take 2wks to return the parts to me. Once I get the final price for the services and shipping costs I'll let you guys know. If I can get off work early enough tomorrow I'll send out the camshafts to Webcam for rewelding/grinding and then I'll only have the head and throttle body to focus on. And if all goes well, I'll have all the machine work done within the next two months and the fun stuff can begin. In the meantime I've been thinking about what else I should replace while I got the engine apart and I may have to look to see what the service interval is for the cam chain. Would be a big waste of an opportunity to replace it if the remaining service life is less than 60%. Trying not to replace every little item, but at the same time I don't wanna be a cheapskate, lol. If most of you are like me, I'm sure you're more interested in the teardown, build up, and dyno run that is to come in the near future. Right now this feels like I'm having to hold my breath without knowing for how long. In other words, I'm dreading it, lol.

Also, it's been a long time coming, but I've wanted to get the suspension rebuilt as I'm now fast enough that I'm bottoming out fairly often on the trails when I get to run at speeds over 20mph. I'm not a heavy guy (185 lbs as of this writing, down almost 40 lbs!!) so I'm sure it's more the valving than the weight on the springs. Either way, I'll be sending the suspension out to Go-Race when the head and TB are being worked since I was told I'm looking at about a 1 month turn around time. Looks like I won't be turning down the overtime anytime soon

Your bike looks great so far. Good work!

dwollie wrote:

Your bike looks great so far. Good work!

Thank you, it's a work in progress, lol.

A little update, the stroker crank and piston came back from Thumper Racing all balanced and ready to go. The camshafts are still with WebCam and I'll be calling tomorrow to get an update on their progress.

In the mean time, I contacted Go Race Inc. and spoke with the owner Travis. It looks like I'll be sending my suspension out within the next week or so. I'll be getting the full build up that he offers as I can only imagine what is going on in the suspension given the fact that I killed the engine in such short order. Really hoping the suspension upgrades match the hype I hear about them. Not that I'm a skeptic, just really looking forward to being wowed by the improvement.

Garage is really turning into a salvage yard, lol.


Decided to use my rifle case as a crate for the suspension. Lets just hope it doesn't cause a fuss at the post office, lol.


On another note, I'm trying to make my bike a little more navigation friendly and decided to add a power source for my phone. Past experiences has shown that trying to use the GPS feature to plot out the trails I ride on kills my battery in short order. So hopefully the only thing I'll be draining now is the data on my phone plan.


A few details of my phone add-on. The phone box and mount are from RAM mounts. The box is a medium sized Aqua Box with the typical ball mount pieces tied into the lower right clamp bolt. Power is provided by a generic wire in power supply with a micro USB plug to match my Galaxy S5. Only a few gripes with using this enclosure. First, the box will fit the phone once you take a dremel tool to the areas where the side buttons are on the phone. Otherwise, the case will turn the screen on and off or just jam the functions on the phone. Secondly, I couldn't run the power cord through the center of the case like it was made to do as there wasn't enough room between the phone and the box. I searched high and low for a tight 90 degree plug to keep everything contained and no luck. I even tried to purchase some extension cords with a 90 degree fitting and then shaved the plastic housing on the plug. Ended up destroying 2 extension cords and surrendered to the idea of making a hole in the bottom of the case. Just shy of a total submerging the box will keep my phone dry as I managed to keep the hole small and the seal comes in contact with the top of the plug so only 3 sides are not sealed. Also, the plug is lower than the case and gravity will help matters further. The source has a switch which can be seen to the left of the aqua box that came with the HDB bar clamps. There are 3 switch mounts and so far I'll be using 2 of them, one for the phone and the other for my heated grips (to be installed later). If I find myself miserable enough in the future I'll be wiring up a heated vest for the winter. I think it may be necessary to add some red LED lights just above the switches to give me an indication the circuit is hot. Would be a real bummer to have my battery drained due to my grip heaters being left on while the bike is off. As much as I like the Rekluse autoclutch, it does make push starting impossible.

Whats the precosess of getting a good compression reading with the auto deomp system? Did you somehow disable it when you meassured?

Jens Eskildsen wrote:

Whats the precosess of getting a good compression reading with the auto deomp system? Did you somehow disable it when you meassured?

Screw in the compression gauge and crank the engine over, it's that simple.

In the manual it gives you 3 values for the compression, high, low, and nominal (going off of memory so I could be wrong on the exact details). I believe the low reading is with the decomp feature deactivated and the nominal is what you'd see with the decomp functioning. Something most people (to include myself) misunderstand about the decompression feature is that it doesn't remove all the compression, only a small amount. If you think about why I had to rebuild my engine it makes sense. My engine had 60psi, which was not enough to carry the engine through 720 degrees of rotation before firing when is was cold. The decomp feature reduces the compression to 121 psi. So if the compression reading meets the stated value when the decomp feature is in play, then it's safe to assume the compression value will be good when running. A bit of a long winded answer, but I wanted to expand on how the system works for the benefit of the group.

Im well aware how the different types of decomp system works, the point was unless the values in the manual i specified to be with a working decomp system, you cant use the reading for much as youre comparing apples to oranges. But 65 sounds low even with decomp, I give you that. Did you test it further, like hot vs cold, oil in the cylinder ect ect? :)

I dont have a manual at hand, thats why I asked.

Im very exited to see your engine taken apart, perhaps even the worn stuff measurred out.

Jens Eskildsen wrote:

Im well aware how the different types of decomp system works, the point was unless the values in the manual i specified to be with a working decomp system, you cant use the reading for much as youre comparing apples to oranges. But 65 sounds low even with decomp, I give you that. Did you test it further, like hot vs cold, oil in the cylinder ect ect? :)

I dont have a manual at hand, thats why I asked.

Im very exited to see your engine taken apart, perhaps even the worn stuff measurred out.

I too had the same concerns when I took the bike to the dealership. When the mechanic told me about the compression being below limits I asked about the decompression feature being the culprit. He was quick to say no and explained/showed me the values in the manual and stated that the compression readings should still be higher than the lowest value given with the decomp system in play. And as far as further diagnostics go, I didn't do any as of yet. I did however for the sake of academic curiosity order the adapters to make my compression tester fit a 10mm sparkplug hole. When I get them, I'll do a compression check with oil and see what happens.

The manual does instruct to warm up the engine before taking any readings, but since the mechanic couldn't get the engine started the test was done on a cold engine.

From the manual:

a. Set the main switch to “ON”.
b. With the throttle wide open, crank the engine
until the reading on the compression gauge
stabilizes.
c. If the compression pressure is above the
maximum specification, check the cylinder
head, valve surfaces and piston crown for
carbon deposits.
Carbon deposits→Eliminate.
d. If the compression pressure is below the minimum
specification, pour a teaspoonful of engine
oil into the spark plug bore and measure
again.

From what the manual says, if my readings improve with oil added, then my rings are culprit. If not, it's the valves, head gasket, piston, etc.

Here are the correct values for compression as my memory isn't very accurate, lol.

Compression pressure (Standard)
850 kPa (121 psi)
Compression pressure (Minimum)
740 kPa (105 psi)
Compression pressure (Maximum)
950 kPa (135 psi)

The manual makes no mention of needing to deactivate the decomp system and the mechanic at the dealership says he doesn't do that for this bike. In summary, I agree with you that it would be important to verify if the decomp system is active or not.

And thank you for the questions, I appreciate the interaction.

Good news! The WebCam camshafts have come in and they look great. There is almost no sign that any welding took place. There is a spot on the edge of the shaft where the metal is discolored indicating the metal was heated. The rest of the cams are covered in a graphite coating and ready for action. I came into an "uh-oh" moment when the decomp system wasn't installed in the camshaft. At first I couldn't find any markings to indicate which cam was the intake or exhaust. Went to the manual and there isn't a dissected view showing how the system went together. Then the ah-ha light came on and I remembered only one camshaft has the hole for the decompression pin to push through. So five minutes later and the assembly was reinstalled in the exhaust cam followed by the camshafts being placed in the cylinder head. I did notice there was a tiny bit of play between the camshaft journal and the camshaft bearing surface. I just checked the manual and it shows .0011" -.0024" is normal and .0031" is the limit. Plasti gage test shows all the tolerances are approx .002". So it looks like things are good to go. If all goes well, Lindsay Machine Racing will have the parts done within the month time frame they quoted me and I'll start the assembly and tuning before the fall riding season.

Parts arrived!


Close up of the cams and the discoloring previously mentioned


Checked the tolerance of the cam/cam saddle, about .002"


On another note, I waited to send out the suspension to Go-Race because the owner Travis will be on vacation and I saw no point to rush getting the parts to him if he was gone. So as I suspected, the gun case got some attention from the post office clerk followed by the annoyingly repetitive question of whether its a firearm or not. Fortunately I didn't have to unpack everything to win their trust, just a repeated verbal disclosure of the contents and we were good to go. It is my hope that I'll have the suspension back before the engine parts so it will make supporting the bike a bit easier.

When I first purchased my bike I noticed the subframe was shifted to the left by about 2". I managed to bend it back to less than 3/4" from center and rode it without issue. Fast forward to now and I found a used subframe for $175 shipped. I pulled the trigger, bought it, and started cleaning it up. First thing was to remove all the rubber bits and hardware followed by cutting off all the tabs and silly things no longer being used such as the helmet lock. Great care was taken to not grind into the tube wall so it was weakened and create a failure point. Now the subframe has a symmetrical look without the mounting bracket found on the left side. As far as paints go, I got lucky and had some Honda silver spray paint I used for my Civic years ago. I gave it a shot and was genuinely surprised how close the new paint matched the old paint. Obviously the new paint will have a cleaner look compared to the weathered paint on the frame and swingarm. And no, I won't be repainting the chassis and swingarm, lol. I may however remove the paint on the exposed parts to give it a brushed look, but that is just an idea for the moment.

The paint comparison on the subframes and bracket shaving


Lastly, looking at the front wheel I noticed a slight bobble in the rim and it appears to have a slight bend. It's most likely when my Tubliss system was leaking a bit and let the front tire pressure get too low which caused me to case the rim on a rock once or 20 times, lol. In truth, its completely fine and doesn't require any attention, but I really want the black rim with polished hub look so I might buy a set of warp 9 or get the factory hubs rehooped with a set of black dubya wheels. The only issue is the warp 9 wheels are heavier due to bigger spokes and beefier wheels. How much? I have no idea nor does warp 9. Adding unsprung weight isn't high on the priority list so I'll have to weigh my options.

Jens Eskildsen, here are the results of the compression test. Lower value is dry, the higher is after oil was added to the cylinder. As you can see, something is wrong. If time permits, Ill see how bad the valves are leaking. The readings are lower than what the mechanic stated, so I can only assume there are things in play such as tester discrepancies, slower cranking speed due to battery charge, etc.

dry test

oiled test


Thanks for reading everyone, until next time!!

No pictures is showing on my computer at work, are they there? =)

Jens Eskildsen wrote:

No pictures is showing on my computer at work, are they there? =)

Yes sir, they were posted with the same hosting website I've used for the previous posts. Could your employer have changed the settings on the firewall? I know my employer has specific websites blocked to include forums.

The results for the compression test were: dry 35psi, oiled 45psi. I suspect the valves are leaking too for the compression to be so low and only improved by 10psi.

I talked to my neighbor who is an avid trail rider and he thinks my last trip to the sand dunes may have caused the engines early demise. Although I took great lengths to seal the intake from the sand, the terrain is taxing on the engine. Everywhere I rode I was at max throttle and fairly low speed (35mph). This did cause the overheat fan to run quite often and I can only assume how the added heat accelerated the wear. When I get all the parts back from the machine shop I'll tear into the engine and share what I find.

Once the engine build is complete I'll be adding a second radiator. I've studied the WR250F cooling and it won't take much to get another radiator on the left side. My biggest hurdle will be the wiring and radiator overflow that will need to be relocated. I seen there is a company that makes side panels much like what we see on real dirtbikes that are designed to fit the
WRR which will allow me to use a WRF overflow tank. The reviews aren't the best, but it seems like the textured finish and the mounting brackets are the biggest complaints. I don't care about the finish since this is a trail bike and the mounting brackets are easy since I do fabrication with metal as hobby. Besides, the lack of side fairings has been a bit of a cosmetic issue for me. The lack of side fairings takes away from the dirtbike look IMHO.

Which fairings are you looking at the Zero G or the Drip racing? I’d like a set but the prices on the are just nuts. Zero G is less but with shipping from Japan they are still almost 200.

Hertz wrote:

Which fairings are you looking at the Zero G or the Drip racing? I’d like a set but the prices on the are just nuts. Zero G is less but with shipping from Japan they are still almost 200.

I never heard of Drip Racing until you mentioned them. I just looked at their products and they're nice, but I think they're better suited to the motard crowd. I was looking at the Zero G side fairings for my future dual radiator project. And yes, the shipping is crazy (almost sportbike prices, lol) which I'm sure is why I've never seen them on a bike stateside. If this bike wasn't a keeper I'd definitely think twice about spending the money. I just hope they aren't fragile as they will see trail use.

Keep us up dated on where thumper lighten piston and try to weight piston assembly?