Vintage Dirt Bike Q & A
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New MT250 owner just joined with a few questions... :)
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Author:  JonW [ Wed Apr 06, 2011 4:48 pm ]
Post subject:  New MT250 owner just joined with a few questions... :)
Firstly, Thanks Nathan for helping me join! :)

Secondly, Ive just bought an MT250 that's a runner but needs tidying up, It fires up after about the 3rd kick but revs pretty high The fuel is old and ive not had the time to check anything over as yet and i dont think its been ridden in a long time, its pretty rusty. So my first question is really about the engine. Since it starts and runs the electrics work and the bore is probably ok, but should i be worried about crank seals when i tidy it up? Naturally Im going to do usual things when i eventually get it home like clean the carb, drop the oil and replace the airfilter etc. but is there anything else i should think about?

Thirdly, The guy I bought it from also has some cylinders that I might be able to buy and some of them might be CR250... Ok, I know I need only the earlier CR type as they have the correct bolt pattern, but once ive checked that how can i tell the CR250 cyls compared to the MT (or even MR) versions?

Thanks for your help guys! I cant wait to get started on this project but it will probably be a while before i get it home and can take some photos, so please bear with me on the pix as I know we all love photos! :)
Author:  JonW [ Wed Apr 06, 2011 11:34 pm ]
Post subject:  Re: New MT250 owner just joined with a few questions... :)
After a long day of google, I can probably answer my own third question... from what i can tell the MT250 cylinder has 3 bolts to hold on the head, and the CR250 has 4... am i right?
Author:  Danny955i [ Thu Apr 07, 2011 1:01 am ]
Post subject:  Re: New MT250 owner just joined with a few questions... :)
Hey Jon, welcome!

I've got a 74' MT250 that I just completely rebuilt. The 73-75 CR250M top-end (piston, cylinder and head) will fit the MT250 with no modification, maybe slight porting on the crank case if you wanted... but it's not needed. MR's bolt on the lower end of the cylinder, not through the head. They also have a square reed-valve intake.

First thing's first... flush the gas. Does your oil-injection work? If so... that's fine for now... if not, mix your gas 32:1.. Use only high-end 2stroke oil like Amsoil... the Wal-Mart stuff, or "chainsaw" stuff is made to pre-mix and not good for injection systems.

If it starts, then revs really high are you turning off the fuel primer? (This isn't a choke lever, it actually sends more fuel to the motor). How far is your idle screw screwed in?

This should be your plan of attack:
1. New gas.
2. Once it runs, turn off the fuel primer and keep it running by blipping the throttle if it wants to die.
3. If it stays revving high, unscrew the idle screw about 1 full turn... if that helps, then do it until you have a nice steady idle.
4. Once that's done... and the bike is warm... and it seems to be running OK... rev it. If it gurgles or bubbles while revving, unscrew the "air fuel" screw on the right-hand side of the carburetor under the exhaust... Keep reving it until it smooths out.
5. Reset the idle.

If NONE of this helps... you may have an air-leak at worst case, and a too-tight throttle cable at best case.

As for your "tidy up" your kick-star seal, and shifter seal are going to have the most wear as they are outside the motor. I had my motor completely apart so I changed everything while I was in there... in reality, it didn't need it. But, it was nice to do for peace of mind... If you do crack the motor open, just ensure you get the proper gasket kit.

Other than that... let me think... just listen for rattles, whines, and grinding from the motor... if all sounds smooth... you should be fine.

Good luck!
Author:  JonW [ Thu Apr 07, 2011 1:12 am ]
Post subject:  Re: New MT250 owner just joined with a few questions... :)
Danny, thank you so much! That's really great advice and I'll follow it when I get the bike home. I will check out the forum and try and find your bike as inspiration... :)

Can I ask what sort of money i would be look at paying for gaskets, oil seals and bearings for the motor? feel free to PM me if talk of prices is not allowed on the forum of course. :)

I should have done a little more about me in the intro... Im a life long bike fan and love my 2Ts... I started with mopeds like the MT and MB50's when I lived in Holland in the mid 80s and had many of those over the years until I sold them all when I left the UK to head to Australia in 2005. All through my life ive pretty much always had some kind of bike, and at some times as many as 10 or 11, some in bits but most running. These days I am a huge RD/RZ fan (I had those bikes in the 80s too) and have several yammys but none of them go... oops! In fact most are being rebuilt as im a sucker for a project! ...but also have Honda love (always have since the early days) with an XL500R which is in bits and a SL125 that I need to get running so my mrs can learn how to ride a geared bike. :) The MT250 is a bit of a departure for me... it has a few things Im not used to... points being one of them. But I love its simplicity and ive always wanted one, it was my dream back in the day to own one when I had my MT5. sad but true... small boy + model range brochures and posters = expensive time 30+ years later as you fulfil your dreams! :)
Author:  Danny955i [ Fri Apr 08, 2011 1:43 am ]
Post subject:  Re: New MT250 owner just joined with a few questions... :)
Awesome!

Gasket kit, $30-40, bearings $20-30, seals $15-20... for a complete rebuild, you're looking at about 100 bucks.. and that's just the bottom-end of the motor.

So, again, that's worst case scenario. You should be fine with a good flush and fiddle.
Author:  mitchie [ Fri Apr 08, 2011 5:47 am ]
Post subject:  Re: New MT250 owner just joined with a few questions... :)
It's the 73 and 74 only CR cylinders that will work. The 75-76 are the same and won't. Also, while the intake is different on the MR and 75-76 CR cylinders, it wasn't for a reed valve as those didn't go on until '78.
I would be looking at the seals closely, especially if it revs when you start it. But first try cleaning it up, especially the jets, fresh gas and fresh plug.
Good luck and have fun. These are great bikes.
Author:  JonW [ Fri Apr 08, 2011 9:20 am ]
Post subject:  Re: New MT250 owner just joined with a few questions... :)
Danny, sounds cheap enough that it might be worth doing anyway, should i buy those parts from uncle Honda or elsewhere? I know the top end rebore stuff can get expensive and depends on which pistons etc. Ive done a lot of rebores and bought a lot of RZ and DT pistons the past few years for my projects as the engines get refreshed. hmm....

Anyway as you said, better to start slow and clean and trys fresh gas/plug. Just got to arrange to get it home and I'll start to play with it. :)

Mitchie, Oh cool. Cheers mate. So the 73/74 have that 1 extra small stud bolt hole in the head and work properly on the MT as they use the 4 long thru bolts, but the 75/76 use the 5 thru bolts pattern?

Thanks again guys for your help and making me welcome to this forum! :)
Author:  Danny955i [ Fri Apr 08, 2011 10:48 am ]
Post subject:  Re: New MT250 owner just joined with a few questions... :)
That fifth hole is for a lock-nut for the head... just extra insurance and ensuring a proper seal on the front of the motor...

I'm sorry... I thought the reeds went in the square block... also thought the 75CR250 jug would work.

Oops!

You can get the bearings from re-mx.com, or you can simply wait til you get the motor, remove them, and go to a bearing shop... yes, they do exist. Search google/yellow pages. They're VERY common bearings and should be readily available/cheaper at a shop.
Author:  Danny955i [ Fri Apr 08, 2011 9:15 pm ]
Post subject:  Re: New MT250 owner just joined with a few questions... :)
Here's some inspiration for when you get your motor cracked open...

I started with this....
Image

Tore it down to this...
Image
Image

Painted this...
Image

And now I have this...

Image


All done in about... 2 months time on my days off.
Author:  woosh [ Mon Apr 11, 2011 10:44 am ]
Post subject:  Re: New MT250 owner just joined with a few questions... :)
Hey Danny did you replace all six bearings. I thought that one of them was hard to find as it was an uncommon bearing. I did all six on my mt but it was a while ago and so I dont remember for sure. My crank seals were bad and crank out of true and it took three tear downs to get it right, lol I bought the tools to check for true after that.
Author:  dsi [ Mon Apr 11, 2011 6:39 pm ]
Post subject:  Re: New MT250 owner just joined with a few questions... :)
The wierd bearing in that motor is the 17 x 42 x 12. You can still get it from Honda.
Author:  JonW [ Tue Apr 12, 2011 4:35 pm ]
Post subject:  Re: New MT250 owner just joined with a few questions... :)
Thanks guys, especially Danny with all that inspiration :D I read you might be going back to the original look with the rear end too, the project is never completed! I think maybe its a good idea to strip the motor and renew this stuff, I intend to ride this bike on and off road and dont want to have to strip it again not long after I get it working of course. I had a look and cant find that funny sized bearing online as I assume its a bike specific thing, most gearbox bearings are it seems on most bikes, sigh. I took my RZ bearings to my local bearing place and all he had was a waterpump bearing, the others he just shrugged and said 'bike bits, its always like this... bloody special bearings we cant get {grumble}' hmm...

Ive had a busy week... Ive been helping my friend who is selling me my bike with his parts and bikes. He had several bits and also quite a few whole bikes in bits so we've been building them up so he can sell them on. So whilst i dont have my own MT in my garage as yet (long story involving injury (not me!) and lack of trailer etc) I have now got plenty of experience in these bikes. One bike we managed to get a nice fat spark but nothing we did would make it run or even pop, not even some fuel in the bore, which was a shame as the rest of the motor looked serviceable. Any ideas on that? Anyway we then moved on and just started on the next one and this second bike had an engine without a piston so we swapped it for another whole engine he had but it seems to have a loose flywheel, which as i sit here and type this I think is common as i guess people removed the points when those became harder to find from Honda, unless i read wrongly that Honda stock ran low on those parts? anyway no issue now as they are online from online sellers now which is cool. Luckily I remember that in the parts i found a set of used points so thats good in case that bike does need those, it would be nice to make another runner. I will grab the piston-less engine as a spare for me as its all there apart from the piston/small end etc Ok it will need a rebore of course but are pistons easy enough to get for these bikes? I saw some Wiseco's on ebay but they had no gudgeon pins, is that normal on MT pistons? Every other piston ive ever bought has had the full kit, apart from OEM honda which came with nothing. hmm....

We did come across an oddity late yesterday in the parts, a standard looking exhaust that had been modified.... now fro the ones ive seen there seems to be types of exhausts fitted to the MTs, one has a straight pipe at the end and one has a wider more pronounced end like a small muffler. This was one of the (earlier?) smaller end tube types with no baffle end, but instead it had the end pipe with the baffle cut off and a longer thinner pipe added. The pipe also seems to have been gutted of all its innards (I could see some welding on the backside) and was about half the weight of the standard pipe.So I assume the spark arrestor was removed and maybe some other stuff as well? What do the assembled crowd think? worth trying on my bike? We also found a pipe modified with a cranked over front pipe, like someone had modified it to be used on a later CR engine with the exhaust exit on the left, looked very strange and not ideal for two stroke power.

So a busy few days and lots of fun to have more dirt under my nails, and good to help out a friend of course, but of course even better ive now had a play with these bikes. all good. Hope to have my bike here by next weekend, all being well. :)
Author:  Danny955i [ Tue Apr 12, 2011 10:19 pm ]
Post subject:  Re: New MT250 owner just joined with a few questions... :)
By the way...

Check this out:

http://cgi.ebay.com/ebaymotors/BOTTOM-END-BEARINGS-SEALS-HONDA-MT250-1974-76-ENGINE-_W0QQcmdZViewItemQQhashZitem3a529221f9QQitemZ250493411833QQptZMotorcyclesQ5fPartsQ5fAccessories

It's a complete kit for bottom end bearings.
Author:  JonW [ Tue Apr 12, 2011 10:25 pm ]
Post subject:  Re: New MT250 owner just joined with a few questions... :)
Wow, Thanks for that mate! Looks a great deal, I will grab a set of those. The same guy has set of tapered steering head bearings, has anyone used his stuff on their bike as I can save a bit of postage if i buy them at the same time.
Author:  JonW [ Tue May 03, 2011 1:39 am ]
Post subject:  Re: New MT250 owner just joined with a few questions... :)
Ordered the bearing/seal kit from ebay and also some gaskets and will rebuild an engine and see how i go with the restoration bike, when they arrive.

With the other (I call it the 'runner bike', my mrs calls it a swamp or canal bike, hmmm) I finally got round to getting the carb off and cleaning it. The (not the main jet, so probably the air?) jet was blocked solid but is better now. put it all back together and started it up... EEEK! 250000000 revs and a fuel running over my feet! eek. i have no ignition key at the moment so am running with the ignition switch plug pulled and it seems to run ok like that but ive no kill switch...hmm... had to pull the white/black wire hear the back of the engine to kill it. When it was revving like crazy all manner of caked on dirt and insect pods were firing off all over the garage floor from between the cylinder fins... LOL

....when my heart and had finally stopped pounding and the fuel was switched off i worked out the carb slide was the wrong way round and that fixed the billion revs thing of course. I tapped the carb but the fuel wont shut off, so just started it with what was in the bowl and it played nice and i got it to idle ok. cool.

Ok this engine isnt the best, Ive had more of a look at it and a few of the case side bolts have nothing to bite into as the 'tabs' on the middle case parts have been busted off and also the brake pedal stop bracket must have been ripped off years ago as the brake pedal has left its imprint in the cover in a few places. Ive fixed the rear brake bracket by making and welding a new one on, but as i have spare engines it makes me wonder if i might use a different bottom end as this one doesnt match the frame number anyway... hmm...
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