Tomberlin Crossfire 150 Rebuild

[subydrift]

I got some more work done on the motor this last week. I got the output shaft replaced and the gear box all rebuilt and resealed. I also got the new clutch, variator with 9 gram rollers, and cvt belt installed and got everything all cleaned up and reasssembled. Now on to the top end rebuild!

I also got the wheels powder coated and the tires mounted so she'll be rolling tonight! I'll post another update tomorrow with it on the ground finally.

Here's some update pics, you can see the old output shaft was twisted and cracked.

 

[subydrift]

She's finally rolling! I'm gonna dig into the engine top end tonight and then its trying to remember how the carb gets hooked up and where the wires all go. Lol.

 

[Grizzlymi]

Looks awesome! Great job man! Wiring always sucks. Good luck.

 

[BaconBitRacing]

It's so pretty! I want to drive it just looking at it. Get it done fast so you can get it dirty

 

[subydrift]

@Grizzlymi luckily I have the new harness from Super GY6 so all I have to do is figure out where to land all the connections. Hopefully…. Lol

I got the engine all gone through tonight and got the new top end all installed, valves adjusted and everything. I’m hoping to get the new stator in tomorrow, all the plastics back on and then the engine back in the buggy. Some other misc remaining tasks are refinish the exhaust (ugly and has a rattle inside), bleed the rear brake, install all the electronic components, and probably tighten the shocks. It has quite a bit of sag.

The new top end has a TON more compression then the old setup. The old piston and head had a bunch of carbon build up, I bet it ran like garbage before. I’m excited to see how she runs!

 

[Denny]

Looks really good! Looks like the engine may have been processing some oil!

 

[Snaker]

Oil can go by the rings or the valve seals, always a possibility.
In these things oil can also leak out of the oil passage from bottom to cam area.
I suspect that it may be a passage leak, caused by bad, broken or missing orings along the cylinder studs.
Did your new kit come with orings for that?

 

[subydrift]

Everything from the main case up was replaced, well, except the cam and timing chain. I added a little copper rtv to the lower cylinder gasket and it got a new cylinder, piston with rings, wrist pin, head gasket, new head with valves, seals, springs, etc. and then a new valve cover gasket too. I also replaced the lower timing chain guide and the timing chain tensioner. I didn't want to pull the cvt cover off to replace the upper guide. Hopefully there isn't any leaking but luckily having done it once this thing would tear down pretty easy again if I run into issues. I did notice that this engine must have been rebuilt previously as the piston "IN" for the intake valve was at the exhaust valve.

 

[subydrift]

Well we had a successful first trip out with the buggy! It fired right up and sounds great. The kids had a blast. I do think I am going to swap in some 12g rollers to keep the revs a little lower. The kids don't drive it all that fast and to have it revving so high right behind your ear is somewhat obnoxious. I think the heavier rollers will keep the rpms down while still being able to push them around the neighborhood just fine. If we ever do any major off-roading I can easily swap the 9g rollers back in or a mix of the 2.



I checked the oil after a couple hours of riding and it was up to the top of the dip stick tube! I guess I shouldn't have filled it when it was flat on my work bench. Luckily I was able to change the oil up there and get the proper amount in it. One thing that is worrisome is the color of the oil. This was just 2-3 hours of run time. It smells like gas also. It doesn't smoke out of the exhaust and it has good power so I'm not sure if this is normal or if I am getting major blow by through the rings? The top end rebuild seemed to go great so I don't know where this is coming from? Any tips? It is also an old motor so maybe the color is from gunk already in the case that is just getting cleaned out? I'll do another oil change and see if it cleans up at all.

 

[Snaker]

Don't recall if you have a oil cooler, but mine seemed to make a fussy oil level.
Eventually I figured out the proper quantity to add on a oil change, sometimes the dipstick level was perfect.
Sometimes the level was high on the stick for an hour or three, then go down to normal.
I suspected a air pocket in the cooler plumbing, although I would check and find the cooler was hot, so........

Your situation sounds like gas is getting in the oil.
A stuck carb float valve can drain gas into the intake if angles are right, I would check that.

 

[subydrift]

No oil cooler on this model.

Is there an easy way to check the carb float valve? The carburetor is a new unit with performance jets from Go Powersports. It has an idle air fuel mixture screw maybe it is running rich? I'm going to check the spark plug today also and maybe open the gap a little.

Performance Carburetor with Performance Jets, 150/200cc

The 150cc Carburetor with Upgraded Jets is a high-quality and reliable carburetor designed for use in a variety of vehicles. This carburetor features upgraded jets that provide improved fuel flow and air intake, resulting in better engine performance and increased horsepower. The precision...

www.gopowersports.com

 

[Snaker]

Here's a quick test, one of many.
Seems from memory that around 5 psi is something of the standard.
I've blown up a balloon and attached it to the fuel inlet nipple.
It will deflate, but you can get an idea of how fast

How-To: Pressure Test Carburetor Float Needle - YouTube

 

[Denny]

Get the engine and rings broken in first. The rings ain’t even seated yet. If the oil is dirty it’s doing its job. That’s ok too.

 

[subydrift]

Thanks Denny. I’m going to change the oil again and pull the carb off and test the float seal to see if I can hear or see it leaking. It seems odd that fuel would be draining into the cylinder with a brand new carb, from a reputable dealer none the less. I wonder if maybe the rings got jostled when fitting it into the cylinder and they aren’t clocked anymore like they should be so its just major blow by?
I just don’t want to look past this and then down the road ruin the engine cause the oil is constantly too thin to do it’s job.

 

[subydrift]

I also ordered a new valve cover to make sure the head vent is clear. I noticed there was some silicone or something globbed in and around the inside and around the outside of the nipple on the original. I don't know if it is causing blockage or whatever but I figure a new one is cheap insurance.

I'm also going to grab a compression tester from amazon and see how it looks. What is the compression supposed to be for these motors?

 

[Snaker]

Thanks Denny. I’m going to change the oil again and pull the carb off and test the float seal to see if I can hear or see it leaking. It seems odd that fuel would be draining into the cylinder with a brand new carb, from a reputable dealer none the less. I wonder if maybe the rings got jostled when fitting it into the cylinder and they aren’t clocked anymore like they should be so its just major blow by?
I just don’t want to look past this and then down the road ruin the engine cause the oil is constantly too thin to do it’s job.

Yeah, that's not what normal break in oil looks like.
Somethings up.

 

[subydrift]

I did a little reading online after googling this issue with the gy6's and one thing sparked in my head. While I was trailering the buggy to our property (roughly 1-1/2 hour drive) I remember I did not shut off the fuel pet cock. I kept thinking I should jump out at a red light and close it but didn't think much would happen so I didn't. I read a few posts about how trailering these things can make the float jump and gas to spill into the intake manifold and down into the case past the rings.

I checked the oil last night, which has had 2-3 hours of run time on it after the change, and it was still somewhat clear with less gas smell. I'm going to change the oil again and run for a bit and see if the problem persists. If it doesn't then I think I can chock it up to me being lazy and not closing the fuel valve. If it still gets the gas smell and grey color then I'll start troubleshooting with the carb.

In the meantime, I'm going to change the valve cover still and replace the fuel lines as the Chinese lines I got on amazon got hard as a rock and cracked at the et cock from bouncing around. Also going to swap in the 12g rollers. I'll keep everyone posted.

 

[subydrift]

Kart has been running strong for the summer. I had a little issue with getting it idling after sitting for a few weeks but I took the carb apart and swapped in the old main jet and cleaned it out and it idles and runs better than before. The suspension on this thing is butter smooth! The front is super active with the softer snowmobile shocks and the damping is a huge plus. I think the next upgrade is gonna be some new tie rods. I want to upgrade the ball joints to a 3/8 heim and use some longer/stronger rods before we really get it in the tough off road stuff. This cart is super fun! I'll get some fun gopro videos uploaded of the suspension cycling soon.

 

[Grizzlymi]

Awesome man! Glad you are enjoying it and it is getting some use.

 

[fdiaz0822]

Got a little progress on the Crossfire done. I got the control arms and shock springs powder coated orange and got the front bumper and swingarm all painted in gloss black POR15. I'll be painting the main frame with the same paint this weekend when the weather is a bit warmer. The orange really pops with the black. I'm excited to get this thing back together!

Where did you get the shocks from I have your exact same go kart and my front stock ones blew out and I’m having trouble finding the size