Hi guys,

I got my seized MK2 engine to Kent okay and took it it apart with my dad. I'm 34, he's 62! Just some background, it seized solid at 70mph in January and this is the first opportunity I've had to work on it.

Album:
https://imgur.com/a/3m3y2

While taking the head off we noticed the gasket underneath slightly obstructed the water coolant channel:
https://i.imgur.com/1TfSWN8.jpg

Question: Is it normal for this to happen or was the gasket not fitted correctly, or perhaps the wrong size?
Question: Would this be a big cause for concern?

It turns out the top end had not seized after all! My dad reckons the piston and bore are not scored at all and weren't the problem. However, he says the piston rings weren't put in right (most likely) something about a key and notch no longer in replace (something like that) and says we need to replace the piston anyway now.

Question: He says because there is no damage so we can just put the same sized piston in again. Does this sound normal or would we be better off reboring to the next size and fitting an oversized piston?

There is no obvious damage visible the 'stator' side. We had wondered if magnet had come out but it looks fine to us.

Got the clutch side open. At first it was completely seized, then we used sockets etc to rock the cogs anticlockwise and clockwise and they eased up a bit! That's a good sign we thought. It now moves quite a bit and then encounters the 'lock' while turning. We're not sure where the problem is. We've ordered the clutch removal holder tool (was only £18) and are waiting for that to turn up. My dad wants to be sure the issue isn't in the outer clutch area. He said looking at the diagrams there are' needle bearings' behind the clutch. He doesn't think they're the problem but wants to rule them out before splitting the case.

During the whole procedure, A LOT of 2 stroke oil came out the engine when we turned it on its side. My dad was very surprised and felt that was an indicator the oil pump was pumping far too much in. When the bike is up and running again I will go on premix for a while and then switch to the pump afterwards when it's all running smoothly.

Question: Is it usual for substantial quantity of 2 stroke oil to pool in the bottom of the CRM250 engine? I was amazed how long it poured out for.

We noticed some separation in the casing at one point:
http://i.imgur.com/eoPMXSJ.jpg

Question: Any thoughts about if that is indicative of a problem? My dad wondered if a gasket was in there?

Question: Any idea what kind of lock could cause a seizure in the bottom end at 70mph? The gears appear to be completely fine.

Any advice will be welcome.

We will update this thread with our progress

Album:
https://imgur.com/a/3m3y2. Looks fine. No problems visible.

While taking the head off we noticed the gasket underneath slightly obstructed the water coolant channel:
https://i.imgur.com/1TfSWN8.jpg No problem this is how Honda designed them all.

Question: Is it normal for this to happen or was the gasket not fitted correctly, or perhaps the wrong size?
Question: Would this be a big cause for concern?

It turns out the top end had not seized after all! My dad reckons the piston and bore are not scored at all and weren't the problem. However, he says the piston rings weren't put in right (most likely) something about a key and notch no longer in replace (something like that) and says we need to replace the piston anyway now.

Question: He says because there is no damage so we can just put the same sized piston in again. Does this sound normal or would we be better off reboring to the next size and fitting an oversized piston? The bore looks very good but you should measure the width before you get a new piston though a one the same size looks a good bet.

There is no obvious damage visible the 'stator' side. We had wondered if magnet had come out but it looks fine to us.

Got the clutch side open. At first it was completely seized, then we used sockets etc to rock the cogs anticlockwise and clockwise and they eased up a bit! That's a good sign we thought. It now moves quite a bit and then encounters the 'lock' while turning. We're not sure where the problem is. We've ordered the clutch removal holder tool (was only £18) and are waiting for that to turn up. My dad wants to be sure the issue isn't in the outer clutch area. He said looking at the diagrams there are' needle bearings' behind the clutch. He doesn't think they're the problem but wants to rule them out before splitting the case. Doesn't look like a clutch issue but there could be a broken tooth jamming the gearbox? You are going to have to split the cases before you find it. Could also be a big end issue but if so you caught it very early in the distructive cycle.

During the whole procedure, A LOT of 2 stroke oil came out the engine when we turned it on its side. My dad was very surprised and felt that was an indicator the oil pump was pumping far too much in. When the bike is up and running again I will go on premix for a while and then switch to the pump afterwards when it's all running smoothly. Did this come out of the sump? Where did it come out? How much is a lot?

Question: Is it usual for substantial quantity of 2 stroke oil to pool in the bottom of the CRM250 engine? I was amazed how long it poured out for. There should be no 2 stroke oil in the sump. If it was it the crank then there should of course be some in there. BUT how long did you store the bike upright without running the engine? Obviously there is gravity trying to pull the oil down so if the oil pump was sealing poorly or badly adjusted there would be a flow of oil into the crank over time.

We noticed some separation in the casing at one point:
http://i.imgur.com/eoPMXSJ.jpg No problem. Just the width of the gasket.

Question: Any thoughts about if that is indicative of a problem? My dad wondered if a gasket was in there?

Question: Any idea what kind of lock could cause a seizure in the bottom end at 70mph? The gears appear to be completely fine. You need to split the cases to see.

Any advice will be welcome.

We will update this thread with our progress

I will guess input shaft bearing. Get the clutch off and split those cases.

We're making progress.

Clutch removed - no issues found.

My father wants to check the stator in details but doesn't have a flywheel puller that fits.

Can anyone recommend one that will fit? Maybe one that can be ordered from Amazon or Ebay?

Loads of Honda pullers on ebay they have different threads on each end and they seem to fit almost any Honda. ~£10.

Hi guys,

It's going well. My dad has got the case split and says the following:

https://imgur.com/a/L0obj#4

"[First picture] is the collection of parts, [second picture] is the cases split with the crank at the front. [Third picture] shows the nearside main bearing, looking at the ball bearing at 1 o’clock it doesn’t look right. [Fourth picture] shows another part of the ball bearing cage has actually broken away, it has split! Something I’ve never seen before, a first time for everything. [Fifth picture] shows another shot of about 3 that have split the bearing cage.

The only reason I can think for this happening is that the ring locating peg has dropped into the case and then got into the space between the balls and the race, then when the ball has rolled over the peg it has lifted off the track and squeezed sideways and broken the cage and that’s why it has seized.

We now need to measure the end float of the conrod, if that is within limits then we can simply replace the main bearings and seals, piston and have the bore honed and then re-build with new gaskets and reeds "

Will let you all know how it goes.