Planet Minis

honda_xrs85

So I have a Takegawa 124 Superhead, it's the older Superhead non +R. So here's the problem: It's slow, even slower than a TB 117 by a long shot. It feels like a 88 Race Head. It just doesn't have much power throughout the whole RPM Range. It has a fresh rebuild, new rings, gaskets, timing chain, and cylinder was honed. Piston measured up fine(was within wear spec), valves were fine, and cylinder walls didn't have any scars or scratches. This has the S20 cam in it. So here is what I have checked so far:

1. Timing is spot on, checked multiple times
2. Valve clearances have been checked tons of times(.08mm, per the manual on Two Bros)
3. Compression (had 180-190 PSI)
4. Leak Down Test (both valves sealed, leakage past rings was less than 10%, which is within the allowed amount)
5. Carb and air filter are clean, swapped carb off of good running bike and it made no difference
6. Cylinder stud top nuts are torqued to 10 Ft-LBS.
7. Exhaust is not plugged
8. May be more that I'm missing

I took a compression test on a TB117 and it read 220-230 PSI. So I'm guessing that the compression on this motor is low, but I can't find out why. Rings sealed fine, valves seal fine, I'm sure the head gasket is not leaking, and I'm pretty sure the correct dome piston is in there. There is no compression leaking out the spark plug hole either. The only thing I am not completely sure about is the piston, as I bought the motor used with that piston in it. I built the motor myself. Any suggestions guys, I'm stumped on this one?

firepower354

Well, that 117 you're comparing it to is no slouch

Kidding aside, did you measure piston to deck at TDC?
Could be the wrong piston, too thick head gasket, buggered porting, piston to bore clearance is excessive, bore is worn (check ring end gap?), spigot pinched in undersized case bore (NO, if it's the set I did) valve job gone to poo, lots of stuff can make 'em slugs.

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honda_xrs85

Yes, that 117 absolutely rips it up, very hard to keep the front end down.

Of the things you mentioned, I can rule out the following:
buggered porting
piston to bore clearance is excessive
bore is worn
valve job gone to poo


I've checked those and the cylinder and piston are fine. Did a leak down test and the valves were fine.

Possibilites:

So it could be the wrong piston, I might be able to take it out today and measure it.

It also could be too thick of a head gasket, the one I got from Takegawa had like 5-7 metal sheets together, but when I took the motor apart it only had one. Does it seem like that's too many gaskets?

The set of cases you bored for me are sitting on the shelf still. The ones I have are CHP pre-bored ones.

What do you mean by "spigot pinched"? I remember when putting on the cylinder, it was a little tight and I had to lightly hammer it on and use the screw that goes into the case to get it on.

Does 180-190 PSI seem low? I know that 117 had a BBR head so the compression is pretty high on that.

gfleck067

what is the motor set up besides the bbk like carb intake and all that stuff might help

sous

++1 for tbparts

xlxrman

I'm kinda helping him out on this bike. He's running Pro Circuit exhaust and a VM26. We put my VM26 off my TB117 on there and it didn't run any different.

sous

i hv a tb 117 on my gorilla bike it can hit 110 kilo around 70 mph with 17/30 gearing all i can say i can do 1 2 3 4 gear power wheelie awsome power

maybe gasket problem try to take a close up pict and post it a wrong gasket installation can do that any problem with gasket your bike will lose compression
on my tb head it has only one gasket ?

firepower354

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honda_xrs85

Really think that's the problem? What happens when you pinch the spigot? Does it somehow create a deformation in the cylinder wall?

p3racer

yes, take the head off and leave the cyclinder bolted on. Turn the engine over by hand. When the piston is at the bottom it should not be any harder to turn the motor over than when the piston is near the top of the cylinder. That could help you find your problem.

p3racer

it could be basically pinching the piston in the bottom of the cylinder due to you having to jam the cylinder into the case deforming the skirt of the cylinder.

50rider340

That head is awesome you said it was an older style head do you know what cam you are running. It should still pull hard down low but up top depending on your cam it can feel kinda flat.

xlxrman

This has the S20 cam in it.

50rider340

hmmm that is strange. This thing should be a monster. Do you know which model super head it is??? On the side of the head where the cam chain is it should have a F imprint on it and then a number, it could be a G and then a number too.

As for all the other info you posted, the compression test is good I pump out 195psi on my 88 super head motor.

When you run it does it smoke at all?

This is going to sound rediculous but are you sure it has a crank in it to make it 124. I dont know if you have done the work yourself somtimes people get things and people say its one thing and it ends up not being what they sold. If that is the case it could only be 95cc's which a 117 would eat up. Sorry for the absolutely rediculous thought lol.

This has got me interested cuz a 124 takegawa motor is a fire breathing pit bike motor.

117s are fast but a 124 should give it a good run for its money.

xlxrman

It says FG6 on the head. Sure it's a 124. Has a Tak crank in there. Took it apart and there was an extra dowel pin in between the head and jug. Put er' back together and it's still slower then balls. Swapping out for my Inner Rotor right now. Let ya'll know how it goes.

xlxrman

Oh, and it was the dowels holding the cylinder from going on. We removed the dowel pins and it slid right on.

firepower354

Piston looks to be well below the top at TDC. We have to cut 1.5-2mm off the 106's to get things all squeezey, maybe you'll need to as well? Clay or soft solder is your pal. Shoot for .030" at the tightest spot, .060-ish for the valves.

The pinch is common on 88's and a few others. Scuffs the snot outta the skirts.

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firepower354

Look at the piston, and the jug spigot. Could be bored off-center and bind anyway. That's why my fixture locates off the dowels and not the OE case bore.

__________________
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Custom FPM parts and engines.
Parts and service for all makes.
Honda Trail Bikes parts and accessories.
Pitster/Piranha/Thumpstar bikes, parts, engines and accessories.

fatcaaat

Could be a 50mm taky crank in there! Let' see a side shot of the cylinder. 69mm cylinder=54mm stroke. 63mm cylinder = 50mm stroke, if its a taky. If not, it could even be 41.4mm stroke. Oh...and there are old school taky cranks that use the 69mm tall cylinder and are only 52mm.

honda_xrs85

The crank is a 54mm, this motor has the longer studs and a 84L timing chain.