Timing chain trouble on tare down

[Swany10]

I'm trying to do a tare down of a locked up 85 250es motor I got on a parts bike. I've never done this before, so forgive me if I'm missing something obvious. I need to get the timing chain off and I can't seem to do it. I took the tensioner off, but there's not enough slack to get the chain off the sprocket. I also wasn't lucky enough to have the sprocket be in a position where both the retaining bolts are accessible. I was really hoping to do a top end rebuild only on this motor, but the only way forward I can see is to break the chain.

Anyone have anything else I could try? Also, I watched a video of a 250sx motor tare down, that guy only had to remove the tensioner to get enough slack, is my motor weird or something?

[Swany10]

I've been trying to use the search to find out more on what I can do here, but I'm not very good at using it yet.

So far I've found a post that says while installing a new chain you have the cam sprocket unbolted to have enough slack in the chain. If my chain is not stretched out, this would explain why I don't have enough slack to take it off. Unfortunately, since I can't access both the sprocket bolts, and have no way of getting the piston to move, it looks like I'll be having to buy a cam chain breaker.

Sound like I'm on the right track here or is there something else I could try?

[207wheelin]

Have you got any idea what's keeping the engine from turning? Did it get water in it? Seized from lack of oil?
If you could figure out why its seized you might be able to free it up. That would make tearing it down a little easier.
Take care
207

[Swany10]

Unfortunately I don't, it came on a parts bike I know nothing about. It was most likely rolled, the front rack and handle bars were all twisted up. I'm guessing it got left out after that, and the cylinder eventually got rusty and locked it up, but it's just a guess. I'm hoping it is that, and that the lower end is fine. I bought the parts bike for other things, so having this spare motor is kinda just a bonus, if I can fix it, awesome, if I can't, oh well won't be too upset about it.

[207wheelin]

Have you tried putting penetrating oil down the cylinder?
Do you have access to the crank bolt to try to turn it over?

[Swany10]

I do have some oil in there right now and letting it sit. Was trying to avoid taking the sides off. If I did that and still can't get any movement, I'll have to go the chain breaker route anyway, so I'm considering going right to that. From there I can get the head off and see just how bad this cylinder is.

[207wheelin]

Seems like you're on the right track! Just let the oil penetrate down around the rings and keep pecking away at it. You'll get it. I've never had my hands on one of the 250 Honda engines but I've freed up some pretty tightly seized engines over the years.
Good luck and let us know how it turns out.
Take care
207

[Swany10]

Having trouble getting pictures on here, the insert image button only lets me put in a url, so does that mean I have to get a photo sharing site set up? I noticed there is an album feature in my profile, can I use that somehow? There's got to be a simple way to do this that I'm missing.

[Swany10]

Managed to create an album, got pictures added to it, but putting in the URL here doesn't seem to work.

http://www.3wheelerworld.com/attachment.php?attachmentid=269066&d=1643990806

did an edit to this post, seems to work now. Here's where I started.

[Scootertrash]

Try removing the starter and take off the flywheel cover, although you may be able to access the flywheel bolt/nut by just removing the slotted cap in the center of the flywheel cover.

If the starter is jammed up for some reason, like rust, it may not be allowing you to turn over the engine. I would use a breaker bar on the flywheel bolt as opposed to an impact. Don't hammer on your breaker bar, be as gentle as possible, but firm.

Do you have any slack at all in your cam chain?

Do you have regular oil in the cylinder or something thinner?


ETA: Here's a link to the service manual for that machine:

http://www.oscarmayer.net/atc/manuals/honda/atc250es-85-87servicemanual.pdf

[Swany10]

Hey, good idea on checking the starter, easy to try. Will probably do that at some point this weekend, and try the flywheel bolt too if I can get at it by removing the slotted cap.

Regular oil in the cylinder, was all I had on hand. I'm sure there are lots of opinions out there as to what is best to use, I'm open to ideas.

The only slack I have in the cam chain is what I got from removing the tensioner. The one video I've seen of a tare down for a 250, removing the tensioner was enough, but I'm guessing that chain was old and worn allowing extra slack.

[Swany10]

I think I have pictures working now.

Here's before tensioner removal. I will be putting the nuts back on before I try moving the piston.

http://www.3wheelerworld.com/attachment.php?attachmentid=269067&d=1643990875

Here's after. Also showing my next problem, the broken stud. I plan to try welding on a nut, just need a welder lol.

http://www.3wheelerworld.com/attachment.php?attachmentid=269068&d=1643990956

[Scootertrash]

Not really sure what the before and after pics are supposed to be showing?

Is there any slack in the cam chain? It doesn't look like it in the first pic, but hard to tell. If the cam chain is not loosening up when you remove the adjuster, something is stuck or bound up in relation to the cam chain adjuster/shoe.

As far as oil for the cylinder, I usually try to use something thinner than regular oil, like the various penetrating oils: Kroil, Liquid Wrench, PB Blaster.....NOT WD40.

[Swany10]

Not really showing anything in particular with the before and after, just kinda showing where I am in the process in case I missed anything, and figuring out how to post pictures since I'm new here. I do have some liquid wrench, I'll start spraying that in there.

[350for350]

Don't be conservative with the penetrating oil either. Use plenty.

[Scootertrash]

Don't be conservative with the penetrating oil either. Use plenty.

Spray some into the intake and exhaust port as well, in case one or both of the valves are closed and rusted shut in that position.....

[Swany10]

Well the starter wasn't it, and no luck yet with the penetrating oil. I'll give it some more time to sit, I ordered a cam chain breaker, so it will be sitting until that shows up at least.

[Swany10]

Well I got impatient, so I got creative and still no luck. First I tried taking out the spark plug and using compressed air in the cylinder. Had 100 psi in there, with about 1/4" of penetrating fluid on the piston. Nope. Then I decided to bite the bullet and take the right side cover off so that I could access the bolt holding on the pivoting chain guide. Got in there fine, got the bolt out, but it still didn't add enough slack to get the chain off. This chain must be in near new condition or something else is up with it. I'm new at this, but everything I can see looks fine and matches up with what I've seen with other tear downs, except for the cam chain slack.

Any other ideas before I throw in the towel and scrap this cam chain?

[Swany10]

Here's after I removed the pivot bolt from the chain guide. If anyone sees something that looks off here let me know.

http://www.3wheelerworld.com/attachment.php?attachmentid=269100&d=1644328807

[IronCreek]

Well I got impatient...
Any other ideas before I throw in the towel and scrap this cam chain?

Don't do that. I've had to wait a while to free up a stuck motor before. See if you can find some Kroil at the auto parts store. Do the valves move freely if you tap on them with a rubber mallet?

All this stuff takes time. Impatience is the worst thing you can do. Let it sit with the oil in the cylinder, top it off occasionally and keep trying with the bar. Oil EVERYTHING you can see that should move and that might help too.

[Swany10]

Don't do that. I've had to wait a while to free up a stuck motor before. See if you can find some Kroil at the auto parts store. Do the valves move freely if you tap on them with a rubber mallet?

All this stuff takes time. Impatience is the worst thing you can do. Let it sit with the oil in the cylinder, top it off occasionally and keep trying with the bar. Oil EVERYTHING you can see that should move and that might help too.

Exhaust Valve moves, but the intake is RUSTY. Out of focus, but here's a picture. I haven't really tried to move it, the valves haven't been where my attention is yet.

http://www.3wheelerworld.com/attachment.php?attachmentid=269101&d=1644337312


So, if this motor is to be saved, it will need the head rebuilt, exhaust stud replaced, and the cylinder bored and a new piston, and that's just what I've found so far. Quite an undertaking for someone who's never done any of this stuff. Good thing I'm going at this as a learning experience, with the hope of having a spare motor for my bike at the end of it. At the very least I'm learning how to work on the one in my bike risk free.

[Swany10]

I think I might try the compressed air thing again with the one way bearing off. Like I've said before, I'm new to this so correct me if I'm wrong, but if the piston happened to be on the up stroke when then the motor stopped, that bearing would prevent me from driving the piston down right? I might work on a way to leave the cylinder pressurized too, give the oil in there some extra motivation to penetrate. With 100 psi in the cylinder, there's about 660 pounds of force pushing down on that piston, seems like it would give eventually.

[207wheelin]

By the looks of that intake pic that thing got a good amount of water in it. Still worth saving but as was mentioned above dont rush it. Soak soak soak and just give it time. Just peck away at it.
Good luck
207 Wheelin

[Shep1970]

Maybe i missed something here but if your just trying to remove the cam chain? to remove the head/cam? Center punch (or not) drill a cam chain pin head off it'll take u less than 30seconds tap out a pin and your done.....

I don't know maybe i missed something here and i didn't read everything....

shep

[Swany10]

Maybe i missed something here but if your just trying to remove the cam chain? to remove the head/cam? Center punch (or not) drill a cam chain pin head off it'll take u less than 30seconds tap out a pin and your done.....

I don't know maybe i missed something here and i didn't read everything....

shep

You didn't miss anything, all of the above has been about trying every other option except that. It's really tempting to go that route to make some progress, but I have the time to try letting the oil soak.

[Shep1970]

Gotcha. understood, think about it though a 35-36 yr old stretched cam chain while your in there should be replaced anyway.

shep

[Swany10]

Seems the problem is the chain isn't stretched, I wish it was then I could get it off the sprocket.

[Pineymudder]

i 2nd the grind timing chain pin and tap it out. ive delt with plenty of water filled frozen cylinders. also if you know anybody with a sand blaster ot will do wonders to clean up all that junk in the head. then THOUGHLY clean head, lap valves and re-assemble. ive actualy replaced timing chains on the quick by grinding connecting and pulling new chain through and tack weld pins when complete. not the best technique but ive done it more times than id like to admit but none failed yet.

[Swany10]

Success! Sort of. I went ahead with trying to take the one way bearing out. Took the opposite hand threaded nut off, but the clutch will not come off the shaft. I can feel a little play in the bell, but the clutch is absolutely stuck on there. Tried heat, tried tapping the bell with a hammer, tried a slide hammer, nothing worked. So now I have a new problem here.

Was feeling defeated, but gave the compressed air another try and movement! Piston started moving enough to allow me to get the other cam sprocket bolt off, and finally that damn chain too. Got the head off, and the jug. Will have to post pictures tomorrow of what I found in there.

[Swany10]

Not surprising, I found a lot of rust.

http://www.3wheelerworld.com/attachment.php?attachmentid=269104&d=1644418351

http://www.3wheelerworld.com/attachment.php?attachmentid=269105&d=1644418368

http://www.3wheelerworld.com/attachment.php?attachmentid=269106&d=1644418386

http://www.3wheelerworld.com/attachment.php?attachmentid=269107&d=1644418397

[207wheelin]

Great work man! Pretty crusty lookin but I've seen a lot worse! You could definitely reuse that cylinder by having a machine shop bore it oversize.
Now on to your clutch issue.
Take care
207

[Swany10]

Great work man! Pretty crusty lookin but I've seen a lot worse! You could definitely reuse that cylinder by having a machine shop bore it oversize.
Now on to your clutch issue.
Take care
207

Thanks! I should probably set up a new thread for this, but what are my options for oversized piston kits these days? I've done a little searching here, found some post that were old enough that some the options are no longer available. Partzilla has rings in .25 and .50 over, but no pistons. Best I've found so far are shindy kits on ebay for .75 and 1.00 over. I'd love to find a .50 over, but my google skills are coming up short. Getting a little ahead of myself here, but worth thinking about what my options will be.

[207wheelin]

I always take em to a good machine shop and let them check the bore and then they tell me what size piston I'll need. A good machinist is an old engines best friend!

[Swany10]

Definitely the plan, just wanted to figure out ahead of time what options I have. Assuming I can get the clutch issue sorted, I'll be focusing on rebuilding the head for now.

[Dirtcrasher]

It's unfortunate, but most of the parts in that motor will be junk.

Once water gets in and is allowed to sit, it attacks anything and everything...

[Pineymudder]

those engines are tough. i helped my freinds son who rescued 2 85 trx250 from a field. both had water in crank case. after we draind and changed oil we got it running with new ignition module. after riding for months he says motor runs real hot. we pulled clutch cover and ive never seen so much rust in and engine before, it was all pilled up on filter screen under clutch cover. it almost busted the screen out. we cleanex it oit and ran much cooler. still going to this day and that was easy 4 or 5 years ago. piston was even froze up but we got that moving with kroil and wrench on crank. doesn even smoke a little. i am still amaized.