Need engine help lol (tbr7)

[Zynice]

Hey yall. Hope yall having a great day. Was riding my bike to work. 5th gear close to 4k rpm, lost all power and hear a pretty gnarly clunk and grinding noise. Pulled over, couldnt get it started and towed it home. Checked spark, plugs are good and not fouled, spark is strong. Checked fuel delivery. Carb is clean and breathing well (air box is clean as a whistle). Slide works and everything looks good on it. Pulled the top rocker box off, valves are good and still in spec to .005. No oil leaks anywhere. no cracks in the block or anything. Oil level is slightly on the higher side but still in spec. Just have absolutely no idea why it wont start. Any and all recommendations are welcome. Guessing down in compression somewhere? Can kick the bike over by hand (was a lot harder before hand and is extremely easy now). With the top rocker box off can see the valves doing what they should be doing. Moves up and down with the compression/exhaust stroke. Do hear a slight grindy type noise when I put my ear close to the cylinder hear when Im trying to kick it. Can provide videos and pictures if need be. If anybody has a video or something how to completely disasemble the top end that would be appreciated too.

[Texas Pete]

Not a diagnostic, but based on what you described, with it kicking over and operating the valves as normal but no longer having compression and being very easy to kick over unlike when new the first thing coming to my mind is the piston head might half self destructed, a hole blew in it, rings broke, etc. If that turns out to be the case its basically tear down the engine and replace the broken pieces with new and if the cylinder need re-honing, do that, or if damaged, think about replacement or rework options.

Removing the head will let you inspect the chamber and piston from the top down but not see anything from the bottom up. If you have an inspection camera you can take the spark plug out and insert the inspection camera into the spark plug hole and view the chamber and top of the piston without having to take the head off.

Also compression test kit will let you remove the spark plug and hook the tester up to the hole and then test what the pressures are like when attempting to turn the engine over.

Just a random video on the process:

[Zynice]

Checked the piston from the spark plug hole. Dont see any visible wear on it. No pitting, no scoring, no oil in the compression chamber. Can the piston moving up and down with no issues, no scraping or anything. Still dont know where the grinding sound I heard before came from. Smell that comes out smells purely of gas, no oil. Dont have a specific tool to measure the actual compression itself, but a finger over the hole and kicking it I can feel a lot of pressure itself on my thumb. Whether or not its enough, I assume it would be enough from other 250s ive worked on. Guessing closer to 100psi. Gonna pull the motor and take off the jug and see if possibly a ring broke on the piston. Drained the oil, normal color no remnants of metal shavings at all. Tried starting fluid in the intake and nothing at all. Rechecked the spark and have a good spark, if anything a bit too much. Up until it broke down it was running extremely well. Any rpm range had zero issues/sputters. When I did break down, was able to downshift from 5th to second before it completely died. Always engine break when I stop, and didnt feel any different at all. Cant remember if I mentioned, had absolultely no throttle response. The kicker does still have some pressure to it (granted much easier than before). But not the point where one finger could push it down.

[XLsior]

no compression with loss of power and no restart, to me suggests a blown head gasket.
There are other possible ways to have compression loss, piston, valves, head crack. loose plug...


You should be able to remove the head without taking the engine out of the frame.

[Zynice]

Originally Posted by XLsior

no compression with loss of power and no restart, to me suggests a blown head gasket.
There are other possible ways to have compression loss, piston, valves, head crack. loose plug...


You should be able to remove the head without taking the engine out of the frame.

I feel ya. Ye was able to get the head out with it in. Ye the piston, bore, everything looks great with minimal to no damage. No carbon buildups, no scoring, no oil in the bore, rings looks good on the piston, Bore itself is even and looks no different than the part that doesnt make contact. Im out of ideas of what it could be tbh lol. Head gasket looked good to me, no knicks, no oil outside of it.

[Mudflap]

How is the electric starter clutch? Flywheel key?

[Zynice]

Decided to pull the whole motor apart. Guess I was completely blind the first time. Top of the piston had to two major crescent shapes on it from what im assuming was hitting the valves. Top piston ring was melted to the piston itself. Skirt of the piston was cracked. Bore on the bottom half had a big scratch from where the piston ring welded itself. Guessing somehow the timing got off? Gonna just use my warranty I have on the motor and get it replaced.

[Deckard_Cain]

Originally Posted by Zynice

Decided to pull the whole motor apart. Guess I was completely blind the first time. Top of the piston had to two major crescent shapes on it from what im assuming was hitting the valves. Top piston ring was melted to the piston itself. Skirt of the piston was cracked. Bore on the bottom half had a big scratch from where the piston ring welded itself. Guessing somehow the timing got off? Gonna just use my warranty I have on the motor and get it replaced.

Also sounds like perhaps it got hot or oil starved... unsure if still stock carburetion and jets....?

Definitely something was wrong that lead to failure. They typically don't just go kablooey.

The clunk you heard could have been some debris getting into the cam and crank timing gears, which would have chewed those up and caused them to skip, leading to valve-piston timing obviously off, and then the collision between them.

[Zynice]

Originally Posted by Deckard_Cain

Also sounds like perhaps it got hot or oil starved... unsure if still stock carburetion and jets....?

Definitely something was wrong that lead to failure. They typically don't just go kablooey.

The clunk you heard could have been some debris getting into the cam and crank timing gears, which would have chewed those up and caused them to skip, leading to valve-piston timing obviously off, and then the collision between them.

Possibly? I dont exactly know the cause for certain. Oil was good, changed less than 1k miles ago iirc. Carbs been rejetted to a 110 main(on the richer side but its how I normally jet/ride my bikes). Oddly enough the last few times I rode it, I noticed it running cooler than usual (live in florida and was in the 50s rather than in the 80s or 90s. Engine wasnt over heated for sure, was able to take the oil cap off right after I broke down. Normally ride in shorts and dont notice the heat from the exhaust at all. I did notice the bottom of the piston was broken too, so mightve gotten into the crank timing gears yeah. Didnt bother to take apart the bottom end, but can if yall would like to know. Place I bought it from is a sending a new engine, just gotta wait for the new one. Hadnt messed with any of the bottom end at all since I bought it (besides oil changes), havent taken any of it appart.

[Zynice]

Oh to add as well. The crank did have a massive amount of play in it with the entire cylinder off. (Good inch of back and forth, foot peg to foot peg if you will). I think I might have a video saved somewhere.... Did also notice when taking it off there was a bit of a gap between both of the two pieces of the cylinder. No oil at all leaking, gasket was really thick and felt like a piece of abs plastic if you will (not very flexible like most gaskets ive seen before but could very well be forgetting things). Maybe a 1/4 inch or more? Like it wasnt flush at all between the two pieces of the cylinder to better describe. Regularly checked to see if there were any oil leaks anywhere after rides and never had any major ones. (Did have a tiny bit come out the sight hole? the screw on the left side with the gear shifter). The hole to find the markings for top dead center lol. Had took it off for a valve check and didnt tighten it down enough so torqued it down good after making sure the o ring was in place. Maybe I over torqued it and caused a piece of metal to go inside the case? Did over torque it and wasnt able to get off anymore, the spot to put a screw driver would just strip out, so just put some epoxy on top of it to make it look a bit cleaner and flush. But that was at like 1.2k miles (blew at 2.4k). The screen for the oil on the left side (24mm bolt) had nothing in it either, just oil.


Come to thing of it, less than 500 miles before it blew I did start hearing a a clicking sound from near the swing arm but assumed it was the chain hitting the swing arm as I took off the bottom half of the chain slider as it was really gunked up and brittle. But my chain was in spec since the first adjustment I did (1/2 of play up and down. Also the part where the shifter goes into the engine can be moved back and forth (from foot peg to foot peg) but it was like that since I got it, and figured it was relatively normal to have some play. Maybe that was the noise I was actually hearing? Like something in the bottom end was a bit messed up and I didnt think of it until now...


Not knocking on these bikes at all. Love the way mine rode, rode better than most 250s ive ever owned. Faster than em too and great torque and low grunt. Mine rung out to 11k or so. Guess something went bad from the factory, or she was haunted lol