79' Ts 250 engine Rebuild

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79' Ts 250 engine Rebuild

New postby JoeH on Sun May 21, 2017 2:11 am

Well I went from getting the parts to rebuild the carb and thinking this weekend would be a dip and rebuild to this;
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I am going to tear it down replace all the seals and gaskets and another questionable parts. I just went through some really great threads here on rebuilds and rest'os ..Good stuff.
At least I know I will get great advice here!

So I just measured the squish without the head gasket and got 1.9mm, with the head gasket that would be close to 3mm …Lots of room.
I am thinking of getting it down to about 1mm. I have a friend who is a great machinist, does lots of work on KTM's so the head work should be possible with the both of us thinking it through, and he can do the cylinder prep for the new piston and the head squish.
It also looks like the inlets are not matched well from the factory but I am no expert in 2 stroke porting so further research will be needed.
Mostly want a down and dirty (well not so dirty) rebuild.

So this was the first time in over 30 yrs I had ALL the bikes I have running at the same time!! Lasted a few weeks :lol: :lol: :D
hate to let my stand sit empty!!
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Re: 79' Ts 250 engine Rebuild

New postby Butcher on Sun May 21, 2017 3:21 am

Front of piston looks seized. Are you wanting more compression for more power / torque?

Your friend has experience with air-cooled 2-strokes ??


This is interesting... Just don't disable the CCIS !!


Frame looks real tidy. Rear shocks are inverted (upside down). Tighter coils should be low to the ground for lower CG...


My 185 is targeted for new crank seals. Why not? After 30+ years and 'x' amount of running out of oil, will be worth it. I have been working on my muffler. I have cleaned out all the funk (carbon etc) and painted with high-temp, mat-paint. Will bring muffler inside to assist in curing paint as less than 10 degrees C here today!

Keep up the good work !
Last edited by Butcher on Sun May 21, 2017 3:21 am, edited 2 times in total.
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Re: 79' Ts 250 engine Rebuild

New postby JoeH on Sun May 21, 2017 1:25 pm

I will shot for the compression to be in the 130-140 range (I think that is reasonable??)
I should meaususe what it has now but as you saw the piston and the bore are a bit buggered.
Does anyone know the stock PSI numbers on compression?

The guy I know has NO experience with the vintage stuff so I will have to be there every step of the way …call It the mentally incompetent leading the blind :roll: YIKES!!!
The vintage guys I know are all out of state and alway SUPER busy , turnaround is sometimes 6 months. I do have one more resource close by that does vintage stuff, I will be calling him this week.

I am debating just going back totally stock but I do think with some info from you guys and what I do know and can learn it is easy and doable. Getting a good squish will make the throttle a bit crisper and give it a bit of usable power and allow me to not fear running crappy gas if needed.
(made a BIG difference on my H2)

Oiling system will be checked and refurbished as needed , dont know why anyone would premix unless they have too and it looks from what I can tell it feeds the crank bearings.

I do believe this thing was seized once, it ran when I got it but it rattled pretty good, I knew the piston was loose and I told my son if he beat it it would fail, the plan was to run it this summer and rebuild this winter……best laid plans and all!!
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Re: 79' Ts 250 engine Rebuild

New postby JoeH on Mon May 22, 2017 12:54 am

OK Im probably going to have a bunch of annoying questions during this process and I do promise to do searches and such…
should I be looking in other sections of the forum ?? Please let me know!!
I have done a few and gained some info but here are a few I haven't found yet.

Pistons…any advice ..lots from stock to XP to Wiseco and Wossner. Which is poplar?? Any thoughts?? Things I should be aware of.

Reeds the stock one look ok at this point but further investigation is needed I will follow the manual.
Should they be replaced? And if so with what?? Daul stage, single stage, stock??

Gaskets and seals?? Stock OEM is what my usual go to is if available .???

I am going to do something with the squish band It atrocious and needs a least a little thought and attention. My concern is there does not seem to be a lot of material to work with in the combustion dome so getting back to stock cc after adjusting may or may not happen with a TS head so CARFUL CONSIDERATION is needed there. Any advice is appreciated.

I am not looking for huge upgrades just want to make informed choices as I go though this motor.

Again sorry for the mundane questions, I just know you guys who have done this have info I need.
Thank you all!
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Re: 79' Ts 250 engine Rebuild

New postby Butcher on Mon May 22, 2017 1:03 am

My '83 TS185ER is VERY hard to kick over by hand. Lots of compression there. I hope that helps.

These bikes run ok on 91, but 95 or higher seems to make a difference.


"it feeds the crank bearings."

Yes Sir, it does!


With a bit of sanding and a hone and may be some new rings, you might be ok! I'd say seizure was caused by running out of 2-stroke oil in the tank. I had a catastrophic failure of my 185. Some idiot (Me) did not screw the plastic oil tank on properly. I think I was distracted or something. I went for ride and the tank promptly fell off. Results weren't to bad as I stopped riding it once it seized! It ran ok after cooling down (and with oil feed!).

Remove rings and clean ring landings. You might get another season out of her. These motors are pretty tough. I have seen much worse and they still run!


"I am debating just going back totally stock"

I would. Just clean up the transfers and match the ports. Trim cylinder head gasket etc as per my porting post.


"it rattled pretty good, I knew the piston was loose and I told my son if he beat it it would fail"

Check the small end bearing. They are roller bearing and pretty cheap to replace. Piston looks pretty toast though!

Good luck.
Last edited by Butcher on Mon May 22, 2017 1:03 am, edited 1 time in total.
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Re: 79' Ts 250 engine Rebuild

New postby JoeH on Tue May 30, 2017 12:48 am

Went through all the threads (I think) . Good stuff.

I have a question on the reed, particularly on the intake track leading to the reed block.

Should it be ported a bit to match the reed block?
Here are some pics hope it helps explain what I am thinking about.
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Re: 79' Ts 250 engine Rebuild

New postby LWC82PE on Tue May 30, 2017 2:58 am

4 petal reed blocks for these should be available pretty soon. They are at CAD stage and i have seen 3D model and not far from CNC now.
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Re: 79' Ts 250 engine Rebuild

New postby Butcher on Tue May 30, 2017 4:41 am

"Should it be ported a bit to match the reed block?"

Yes. There is some info on my porting page (on the 125 or 18 section??). I have matched the reed cage to the barrel. Also, there is a mot for the two screws that holds on the 2 reeds and stoppers. Let me know if you can't find it...


I like what Mr. LWC82PE is saying!!!
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Re: 79' Ts 250 engine Rebuild

New postby JoeH on Tue May 30, 2017 5:00 pm

LWC82PE wrote:4 petal reed blocks for these should be available pretty soon. They are at CAD stage and i have seen 3D model and not far from CNC now.


That will be a good mod!


Butcher wrote:"Should it be ported a bit to match the reed block?"

Yes. There is some info on my porting page (on the 125 or 18 section??). I have matched the reed cage to the barrel. Also, there is a mot for the two screws that holds on the 2 reeds and stoppers. Let me know if you can't find it...


I believe I have found some of the mods.
I did see the screw mod but nothing on matching the reeds to the block.
Seems simple enough , a nice smooth transition , or maybe a very simple slight curve to promote laminar flow , I know they "wing" transfer tunnel separators to promote laminar flow but I am not a porting expert and don't even own the tools to do it.
The reed to block can be done with a simple Dremel.

Also I may match the exhaust and exhaust port and transition it back into the exhaust port
And MAYBE widen the exhaust port I believe it could be widened by 3 mm but I won't raise it, don't want to change the power band to much and I ma not sure the Dremel will allow me to widen the exhaust without a right angle.

And I am woking on getting the head squished and will probably move to an o-ring instead of the stock head gasket. This should allow to take a bit less of the head and still get a good squish band.
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Re: 79' Ts 250 engine Rebuild

New postby Butcher on Wed May 31, 2017 12:17 am

Sounds like you know your stuff. Laminar flow is partly it. Wave propagation is also necessary! Ugh.

I just matched the transfer ports to the barrel. Do this with crank cases apart. Screw one crank case half on at a time. Use your fingers! one can feel any mismatch.

Match reed cage. I used dremel with combination of the tubular sand paper thingymabobs and whatever the other part was called. A metallic tool. Ugh, I'd have to take a photo or steal one from google. Will do later.


I matched everything from airbox, thru to exhaust. The exhaust port is where the gold is. The f***er is not even close to being matched to the exhaust manifold. There I'd widen the orifice to match the transitional point to the exhaust pipe. DO NOT MAKE IT LARGER. THIS WILL STUFF THINGS UP. Just get it shaped opposite to the carb inlet, which is conical for a reason. TO SPEED UP VELOCITY OF AIR! Exhaust is to slow it down.

Think of a rolled up piece of cardboard or paper with you shouting into it. Amplification me boy! Old gramophones worked the same to amplify (make bigger) sound from the needle and diaphragm.

It is not hard. Dremel is good but one needs a rats tail file rasp, bent at the tip. Heat and gently bent it. Files are brittle high carbon. Then quench your hot new tool in water. Very handy.

Also sandpaper. Wrap a small bit around finger and go for it. Emery paper is ideal, or 300 grit. Rinse in in water.

Don't breath the Al into your lungs!


Airbox to carb, carb to barrel, barrel to exhaust. You get the point. Just leave all the stuff factory but just invest the time (unavailable for mass production) into getting it the way it should be on paper...




With 6 petal reed, I think you would need larger carb and airbox, plus exhaust mods. The area of all these things matches. Bigger carb will mean enlarging airbox, etc.


The airbox inlet snorkle is same area as the carb is, for example.


Oh and don't forget to trim the cylinder base gasket around the transfer ports! these swines can encroach and obscure the ports! Gasket can be placed onto crankcase once it has been assembled (minus the barrel, of course). Genuine vs after market gaskets? No idea, but blue print it.


Using thinner cylinder head gasket can adjust port timing and can be easily reversed. Never done this however, I prefer reliability over top end power (and less heat means more power thus torque!)
Last edited by Butcher on Wed May 31, 2017 12:17 am, edited 1 time in total.
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Re: 79' Ts 250 engine Rebuild

New postby JoeH on Sat Jun 03, 2017 1:38 pm

Thanks for the tips on the files! and the rest of them just never thought about the file thing before that will work well!
And I agree about the reliability, my plan is to mostly just blend the surfaces and get it as it should be with no major mods except to the head.
I am still debating the exhaust port widening, I know there is power to be had there and not just top end power, in theory would give good mid and top end without much loss if any on the bottom, but thats theory and without a different exhaust it might be pointless and I am not changing the exhaust.
Blending and matching like you said , thats the best and there are some bad areas as usual with stock.

I am hoping the guy helping me with the head will let me take some pics as we go about doing it so I can post them for fun.
Cylinder is getting bored hope to have it back next week , parts are arriving daily. I haven't split the cases yet but the clutch looks perfect and all the components inside the clutch side look perfect.
Today I am going to weld up some simple brackets so I can pull the rotor with a puller instead of a slide hammer. I dont own a slide hammer and the thought of whamming on the crank and bearings …. Probably over thinking but it won't cost me a new tool either so win win.

And I really DONT know what I am doing at all, I follow set rules that usually work and have been figured out by others with whatever I tune.
I can't do the math, I can't do the testing, I can't understand airflow or resonsace in 2 stroke tuning….I do know air does not like corners and it likes to either expand or constrict without "steps". I know turbulence can be good and it can be bad and figuring out the where and why..I can't, I have tried and found I am too old and to stupid :roll:
So I have leared the hard way to take the advice of wise council or risk ruining a perfectly good motor!
( Which I have done in the past :oops: )
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Re: 79' Ts 250 engine Rebuild

New postby Butcher on Sat Jun 03, 2017 11:55 pm

"Thanks for the tips on the files!"

I stole that idea from somewhere.


Puller is good idea. I have one for the 125's. The 185/250 is different. I just use a basic puller as I only remove flywheel when necessary. Very useful tool...


"And I really DONT know what I am doing at all'

Common sense is useful. So is taking your time and being observant. Manual exploded diagrams are mandatory (when they don't contain mistakes!). Yes, widening exhaust port is good. Piston rings get a harder time. Chamfer the port lips, or round them (better). Lips should not be sharp to feel. This eases the rings back into their grooves without f****ng them.

"I can't do the math"

Search for "online calculators". Fancy web sites where you punch in numbers and click "calculate" or whatever. Makes one lazy though!


"I can't understand airflow or resonsace in 2 stroke tuning…."

Breathe in thru your lips with lips puckered, then widen them. More air gets in. To wide lips means less air actually gets into your lungs! I used to use this puckering technique during running / rugby practice when I was young and fit.

Resonance is like blowing across an open stubby beer bottle. That whistling sound is resonance. Less beer, lower frequency of sound. Frequency is same as engine rpm. The 'pipe' term is just like the frequency (rpm) of the note produced by the bottle.


"I do know air does not like corners"

It bounces off. Go into a hallway with a bouncy ball (those bright coloured small ones) and throw it as hard as you can. It bounces everywhere. Or think of pool / billiards (I suck at these games!). Imagine sitting by a stream and watch the eddy's and whirl pools (don't fall in).


"constrict without "steps""

Yes, steps = bad, tapering not so bad, Constriction of air flow (velocity) causes air to speed up (positive velocity) and opposite for widening.


Tuning is a black art that I no not much about. Give me time and a dyno and I could tune an engine. I'd expect to blow something up though!


Mathematics is just a way of explaining things. Nobody's fav subject. -Can be learnt though. It is very logic based. Engines are more of a "feel" to me...



The TS250 has lots of torque, by all account (I don't own one). My wee 185 has plenty of torque. These bikes will benefit from better suspension, especially at the rear!
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Re: 79' Ts 250 engine Rebuild

New postby Butcher on Sun Jun 04, 2017 12:10 am

Here is a photo of my 185 exhaust port. Notice the lip on the bore sleeve? Grind this so it matches the Al barrel but DOESN'T affect the bore timing. Notice how I widened the outlet where the exhaust plugs on? I didn't take any meat out (by widening). I just matched it to the exhaust tube. The spent gases and some unburnt fuel has to come back into the cylinder for the next compression stroke (super charged). That gas / (mostly unburnt) fuel does not like steps or obstructions! These are the areas to work on.

01.jpg



Here is a before shot. I had to remove 3-4mm of metal to match it to the exhaust header. This photo was not the final completed one.

05 (before).jpg



Here is the exhaust header. It had blobs of weld and rubbish in there. Get rid of it but DON'T make a hole in the header!!! Rinse filings out with petrol.

Exhaust 01.jpg



I had to remove some meat on the barrel where the reed cage screws on. Just remove the reeds and screw on to barrel. It can rotate slightly (twist) with screws loose. Find the best spot and mark with vivid marker. Then use vivid to mark out on the barrel the bits you need to remove. DON'T damage the rubber on the reed cage! the reeds are one way valve. Blow into it, then suck. It will make a nice sound (this is resonance again!). Sucking, you should not be able to, if reeds are in good condition. Also, shine a light into the reed cage, you should see very little, if any light come thru. The reeds will be pulled shut in action, so don't be too fussy!!! Photos are on this forum somewhere. Search for "reeds" or something.

Ports d.jpg
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Re: 79' Ts 250 engine Rebuild

New postby JoeH on Mon Jun 05, 2017 11:32 am

Stupid freaking magneto F#@^#%^@&@* :evil: :evil: :evil:

Two attempts so far and it won't budge… First attempt I broke the bolts, so I got some hardened 12.9's I tried last night but got it to a point and then I left it under presser from the puller and liberally coated it with penetrating oil ..this morning I went down and put some heat to it , not a lot didn't want to burn anything up, hit it with the impact and NOTHING bent the metal brackets I made to use the puller and bent the hardened bolt heads a bit.

Tonight I am going to weld some more braces on the brackets I made to keep them from bending , there 1/8" angle I thought they would be strong enough but NOOOOO. I will keep adding heat and penetrating oil until I get it off …OR I WILL TORCH IT OFF!! :P

Haven't had one this stubborn in quite some time. My old Gs1150 suzuki has given me trouble in the past but it is slightly different and you can get it nice and hot without worry.

I guess if I toast the stuff behind the magneto I can replace it :|
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Re: 79' Ts 250 engine Rebuild

New postby Butcher on Tue Jun 06, 2017 12:02 am

Don't heat it too much. the magnets are glued on. Also magnets don't like to be heated or bashed as they loose their magnetism (loose their magnetic domains to be precise!).



I'd take my time and lay bike on RHS, squirt some CRC5.56 down there and let sit for a while... Mine was a PITA to get off for the first time. They gall themselves on tight! https://en.wikipedia.org/wiki/Galling
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