GX140 build

[areams]

Awhile ago I posted a few questions about the gx140 and if billet Ross and other parts were interchangeable and had great success with help. Thanks! Probably will have some more questions along the way but reading some stuff on here has already helped me out a ton! Like when I looked for 10 minutes for the lash cap for the intake valve only to realize it doesn’t have one after reading a few posts on here...

I figured I’d post my progress and some photos on the build so far. My goal is to go from the rated 5hp to hopefully 8ish? This engine will be fitted to a custom made mini bike that I am soon to start.

My list of mods to the engine include:
Billet rod
Gov removal
CL2 Cam
8 degree key
22lb springs
Reinforced rockers
Port and polish the original head as best as I can
.010 head gasket
Jetted Carb off of a 208cc engine (for now)
Air filter/header pipe
Shorter fins on the flywheel plastic
Performance Spark plug


I was able to plastigage the rod today and had .002 clearance or maybe .0025. Got it cleaned and installed the piston on the rod along with a new set of rings that were gapped at roughly .010 so I left them. Also was able to get the valves lapped back in and the head reassembled today.

 

[landuse]

Looks good!!

 

[areams]

Made some progress today but ran into a snag..

I ordered some of the reinforced rockers from NR Racing and it seems like the pivot nut is not going to go on far enough to get the lock nut on the rocker stud far enough. Anyone had this problem before? Here’s a picture with the pivot nuts tightened enough to where the rockers are somewhat snug on the valve tips.

 

[J.S.@SMS]

Not sure about the 140s but they go about another 1/4" down on the gx200. Let's see what other people think. Also the rockers should not be snug, you should be able to feel a bit on play in the rockers, usually about 6 thousandths for the exhaust and 8 thousandths for the intake on the gx140. I may be wrong but that's what it was last time I checked.

 

[areams]

Not sure about the 140s but they go about another 1/4" down on the gx200. Let's see what other people think. Also the rockers should not be snug, you should be able to feel a bit on play in the rockers, usually about 6 thousandths for the exhaust and 8 thousandths for the intake on the gx140. I may be wrong but that's what it was last time I checked.

I don’t have them set yet, I was just giving reference to let people know they are softly “tightened” to show I can’t even turn them any further if I wanted too.

I believe my cam sheet said .003 for both intake and exhaust clearance, I could be wrong but that number is sticking out right now. I’ll check to be sure when I am setting them up.

---------- Post added at 08:39 PM ---------- Previous post was at 08:31 PM ----------

I should also note now that I am thinking about it that I bought new valve tappets to go along with the new cam. I ordered ones for a GX160. Does anyone have a measurement for the overall length for the tappets out of a GX160 I could compare to the ones I took out of my 140? I would measure mine but if I don't have to take the side cover off that would be great. That't the only reason I could think that these wouldn't be setting down far enough now..

 

[bob58o]

What about shorter pushrods?
Would that help?

 

[areams]

After doing a little more digging, seems I have ordered lifters for a gx200 accidentally instead of for the gx160. Must be a difference in parts since there are two different listings for them on the NR Racing website.

Can anyone confirm if they are different sizes between lifters for the GX160 and the GX200?

 

[bob58o]

160 lifters in a 200 block need longer pushrods, so 200 lifters in a 160 (or 140) block would probably need shorter rods.

http://www.nrracing.com/product-p/cmpr-55.htm

GX200, BSP "Clones", 6.5 Chinese OHVs

5.260 Stock Length; Use with stamped Rocker Arms
5.160 (-.100); Use with Billet & Roller Tip Rocker Arms
5.110 (-.150); Use with Billet/Roller Tip Rockers along with extensive milling (>.065")
5.440 (+.180); Allows use of 160 Lifters in 200 blocks to reduce valve train weight. Reduces combined lifter/Pushrod weight by approx 7%. Use with stamped Rocker Arms
5.340 (+.080); Allows use of 160 Lifters in 200 blocks with Billet or Roller Rockers. Also use with some Aluminum Rockers

 

[65ShelbyClone]

5.260" is how long the stock 140 pushrods are from my engine. 1.196" is how long the lifters are. I can't find a reference to 160 or 200 lifter lengths anywhere, just that the 160s are shorter.

I suspect that 160 and 140 lifters are the same though.

Fun fact: I just ordered a hemi head to put on my 140 for experimentation. Compression ratio might be around 6.5:1...

 

[areams]

Thanks for ge help guys!

I just ordered another set of lifters for the gx160. Luckily they aren’t very expensive ringing in at about $8 total shipped.

 

[bob58o]

Fun fact: I just ordered a hemi head to put on my 140 for experimentation. Compression ratio might be around 6.5:1...

6.5 :1 CR sounds ideal for boost. LOL

 

[KartFab]

good luck man, don't forget to check your rocker arm to valve tip spread.
at TDC on the compression stroke, use a dry erase marker and mark the tip of the valve/lash cap (where applicable) and don't worry about lash, just finger tighten to zero lash, then rotate the engine over a few times and make sure the rocker arm tip is rubbing on the right spot on the valve. It should be an even wear pattern on the center of the valve tip. If it is toward the top or bottom of the valve, you might have the wrong valvetrain geometry.

I would hate for you to run the engine and have the valetrain fail. its an easy way to check and only takes about 5 minutes to do.

 

[65ShelbyClone]

If the contact patch is closer to the rocker side, that means the pushrod/lifter package is too long(as the picture shows). A contact patch on the non-rocker side means they are too short.

Either situation will increase side loading on the valve and thus increase wear on the guides.

The pushrods being too long will also increase valve lift because the valve is contacting the rocker further outboard, but again, it comes at a cost.

6.5 :1 CR sounds ideal for boost. LOL

No comment.

 

[areams]

Interesting thought on the marker on the valve tips to check the rocker path, never thought of that! I’ve always used other ways to mark it that aren’t as clean. Great tip! I’m not new to engine building just new to building these. Did the same when I built my 450 horse small block with roller rockers.

Like you said always better to take the extra steps to check when building than to have it shell after the first run. I’ll update once I get the lifters installed.

 

[areams]

The new set I ordered in described to fit a GX160 measured in at 1.995" which were identical to the ones I removed originally. There is roughly 3/16" difference between these and ones for the GX200.

 

[areams]

Has anyone ever tried to cast their own intake manifold for a mikuni carb? Thinking about trying it for my build.

 

[bob58o]

Has anyone ever tried to cast their own intake manifold for a mikuni carb? Thinking about trying it for my build.

Somebody on here has tried. I don't remember who. I'll try a search and see if I can find the thread.

If the studs spacing is the same as on a gx200, they are fairly cheap.
GoPowerSports sells em for about $20.

https://www.gopowersports.com/manif...-9gCpOUxbD29S-Xo5PSaoBIGgSp-GLScaAtw6EALw_wcB

https://www.gopowersports.com/manifold-for-6-5hp-clones-predators/

 

[areams]

Somebody on here has tried. I don't remember who. I'll try a search and see if I can find the thread.

If the studs spacing is the same as on a gx200, they are fairly cheap.
GoPowerSports sells em for about $20.

https://www.gopowersports.com/manif...-9gCpOUxbD29S-Xo5PSaoBIGgSp-GLScaAtw6EALw_wcB

https://www.gopowersports.com/manifold-for-6-5hp-clones-predators/

Ya I have found them for around 20-25 shipped, just thought it would be fun to try and cast one and wanted to see what people have done. I’m not good enough with the search function apparently yet to find anything.

 

[65ShelbyClone]

Anything new? I did some assembly myself.

 

[areams]

Just got it started and cam broke in today! Ended up going with a Chinese mikuni vm22 instead of the standard type carb. Runs great, revs great and sounds great!

Only thing I’m curious about is what RPM do these idle at after similar mods have been done? I can get mine to around 1200-1300 before it will want to start to die if I adjust down further. Haven’t done much tuning work yet but figured I’d be able to get it a little lower easier than I was today.