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4 day old TB 88 = dead

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HRC

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Discussion starter · #1 ·
Well, after only 4 days..... my TB 88 quit running. I have been tuning it the past couple of days and it's been running strong..... with just a slight low end bog(like most TB 88's). Anyway, I was going down a long downhill..... going for a top speed run when it failed me. I was topped out and held the shifter up(for nuetral) to coast a few extra mph's out of it(I have a speedo). Right when I lifted the shifter and let off the gas...... POP! It died. It has no compression. I thought maybe it was a broken cam chain but I removed valve covers and valves are turning when I kick it over (with my hand).



So, I just thought I would post up what happened and see who can guess what the problem is.... before I tear it down and find out the answer tommorrow. My guess is a bent valve. :p



I was quite surprised at a failure this soon with such a solid kit. :cry:
 
#4 ·
what spark plug are you running, when mine blew up, it was from the spark plug being to hot of a plug, it was a cr6hsa instead of a cr8hsa, it ran real fast tho, the bike still runs mint too after i oil sanded the top end, mine only lasted me less than a hour after i put the kit on, lol
 
#9 ·
ive never had good luck with that T-B stuff ,im surprized you think its a solid kit....ive had pistons that were more oval then round ,and more then a few broken valves.....but i guess the stuff is so cheep you can build it 3 times ,compared to a good kit....
 
#10 ·
Nero said:
what spark plug are you running, when mine blew up, it was from the spark plug being to hot of a plug, it was a cr6hsa instead of a cr8hsa, it ran real fast tho, the bike still runs mint too after i oil sanded the top end, mine only lasted me less than a hour after i put the kit on, lol
Click to expand...


That's the spark plug I'm running in my TB88 with stock head. Should I be worried?
 
#14 ·
HRC said:
Well, after only 4 days..... my TB 88 quit running. I have been tuning it the past couple of days and it's been running strong..... with just a slight low end bog(like most TB 88's). Anyway, I was going down a long downhill..... going for a top speed run when it failed me. I was topped out and held the shifter up(for nuetral) to coast a few extra mph's out of it(I have a speedo). Right when I lifted the shifter and let off the gas...... POP! It died. It has no compression. I thought maybe it was a broken cam chain but I removed valve covers and valves are turning when I kick it over (with my hand).



So, I just thought I would post up what happened and see who can guess what the problem is.... before I tear it down and find out the answer tommorrow. My guess is a bent valve. :p



I was quite surprised at a failure this soon with such a solid kit. :cry:
Click to expand...
Hopefully its and easy and painfull and low-cost fix.



Post pics of what happened so we can all hope it doesn't happen to us!
 
#15 ·
The real problem is the fact that you where going for a top speed run.

You may have overrevved the engine which caused the valves to float and thus kill a valve.

I'd be willing to bet that the piston is broken from hitting the head.

Most of these kits are designed as motocross style riding. Varing RPM.

With roadracers, holding it WOT for periods of time will stretch the rod at high rpm and will make things touch.

A KLX rod will stretch .030 at 11K with a 62mm or bigger piston.

A CRF rod will stretch .020 at 11K with a 50mm or bigger piston.



If People are roadracing these Off road based engines, you will need more clearance.



Just letting you know.



Sorry about your blow up.
 
#17 ·
RySem said:
What ever happened to break in period? 4 days and you're taching the thing out for an extended period of time? Seems a bit soon to me.
Click to expand...






The only thing to break in on a CRF based engine is the rings and the cam.

The cam will only take a few minutes to set with the rockers and the rings need High RPM to develop enough pressure to seat the rings to the cylinders.



I break ALL my engines in this way.



Fire up and let high idle with my hand and not the choke ( extra fuel from choke circuit will wash away the oil from the cylinder and can produce scuffing. )

Make sure there are no leaks while revving the engine to moderate levels of rpm. Never wide open or red line ( yet )

Get engine up to temp (at lease 160 on temp guage ) or the clutch cover is warm to touch.

Turn off engine.



Get to track. Fire engine up the same as before. Put in gear after warm up and take first lap at moderate rpm's. WOT is good but not necessarily redline.

2nd lap.



Ride likes it's for your life.



People have this thing about taking it easy for the first few hours of riding. Doing so will only glaze your rings and you will have a slow engine.
 
#19 ·
this is all great to find out since im using a tb88cc kit on my 70 for RRing/motarding ..maybe at the go kart track it wont be WOT much though..still not great news to be hearing probably shoulda just bought a gpx,lifan,or sdg motor
 
#20 ·
schofell84 said:
by"hand" do you mean with the throttle or are you choking the carb with your hand over its mouth?
Click to expand...






I'm using the throttle to modulate RPM.



The reason for the choke ( or fuel enrichment system ) is because when an engine is cold and dry. The needed fuel that is required for combustion is stuck to the port walls and valves.

With so much of the fuel "wetting" those surfaces, there isn't enough to keep the combustion process going, so hence the choke was invented.



Problem with the choke is that if left on to long or too rich. That extra fuel will clean the cylinder of oil which can lead to piston scuffing.



Never just fire up an engine and leave the choke on for minutes at a time. You are doing more damage than good.
 
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