OzVMX Forum
Marque Remarks => Maico => Topic started by: JC on August 23, 2008, 11:27:23 am
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Gents,
Just revisiting this topic after catching up on back-reading on page 5.
Have any of you followed thro on building one? Mention was made of using a 400 sleeve/barrell, but the 400 engine had 13mm longer stroke. (83 vs 70mm) I would have tho't that would cause major problems in using a 400 barrell or sleeve on a 250 bottom end.
I would have tho't it better to make a new liner to suit the 400 piston (77mm) & 250 stroke. I recently measured a 250's cases & it seems the cutout in the cases for the cylinder spigot is sufficient to take a 400-size sleeve, but not sufficent to take a sleeve made for an 80mm Yam 360 piston w'out machining (which would give 351cc).
Another possibility is to adapt a Yam top-end, something I wanted to do back in the day (as mentioned in another post), but never had the resources.
Mention was made of the Maico at CD2 featured in VMX. I talked to him/them at CD5 & by then he/they had 2 modified 250s. He was a little guarded w his info, but it seemed both had specially made sleeves, one to take a 77mm 400 Maico piston, & the other to take an 80mm Yam 360 piston.
Does anybody on the forum know more about those bikes?
PS. Mark, I think the SA racer who built/raced a 326 was Geoff Flink wasn't it?
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That's him, Geoff Flink from Port Pirie. My 350 squarie is actually a factory 326cc. I rode the bike Geoff Flink did for another bloke (can't recall his name atm) and it was a sweetie. It transforms the ordinary 250 into a rocket.
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Kawboy, with the booming US economy, I have been very busy just keeping the elecrticlty and water on ;D ;D. I do have a 250 AW engine and a std 440 piston, though I planed to locate a 400 piston. As far as the sleeve in the 250 barrel, check out the post I started about the 75 326 that Big K sold-I think womabt bought it. It has a sleeve in the 250 barrel. I thouhght about using the 400 cylinder and machining down to use on the 250 lower-as the porting changes when you take a 250 cylinder out.
Sure you can tune the intake and exhaust length, but the transfer area is reduced. That said Big K's old 326 reputablty runs like a rocket-so it may not be a problem .
My thought was jsut to optimze the combo as much as possible, and from everything I have learned-transfer area is the most signifigant part of power production-all other factors tuned optimally , of course.
I love this discussion, would love to get the $ to pursue it-I am not sure when I can ever rake up the $ to try to buy my old 77 440 back, so I really want to build a 76 chassis with a 326 engine. How did you measure the 250 lower opening? I suppose a digital caliper would suffice? I will go measure mine and reporrt back.
Thanks,
MJ
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MJ,
Yes I did read KigK's posts. As I recall he only mentions using a 400 piston (not sleeve). Others seeemd to have jumped to the conclusion he used 400 sleeve as well.
Unless we're talking about a blank 400 sleeve, I'd have reservations about it working w a cut down 400 barrell/sleeve w'out a lot of juggling around, grinding & machining to get the porting/timing & barrell height right. A 400 sleeve w the ports cut in for a 400 engine still has an 83mm stroke. A 13mm diff in stroke is a big diff to get ports & timing right. (Seems to me there was a bit of misleading info on the previous 326 Maico posting, curently on pg 5 of the Maico Marque Remarks, but I could be wrong)
I don't have the specs for a radialfin 400 engine, but I do have the squarebarrel 400 specs. If the radial is similar in port heights (& I suspect they are - they seem to be typical of Maico engines of the day) you'd have to take about 10mm off the top of the sleeve to get the ex & transfers anywhere near the ballpark & lining up in the 250 barrell, & you'd have probably cut off the flange on the top of the sleeve by then, which would brings other (fairly major) complications. And you'd still have to adjust the bottom of the barrell to get the piston in the right spot (which I think would still cover about 3mm of the ex & trans ports at BDC). Not insurmountable, but not straightforward/easy either.
The bottom of the inlet in the sleeve will be a fair bit lower than the port in the 250 cyl, but thats not a bad thing if the port in the barrell can be lowered to match, cos you need a fair bit more inlet duration & area. I'd suggest aiming for about 170deg duration to start with & adjust to suit from there.
It was a 73 or 74 250 bottom end I measured. From memory the spigot dia in the cases was 85mm I think. Sleeves are commonly 4mm thick, so for a 77mm piston, the sleeve would typically be 85mm dia - & fit right in. I suspect Maico used the same cases for 250 & 400 radialfin engines in those days. But I don't have any of these things in front of me to check.
You'd need to check everything yourself before you started.
Done properly, I have no doubt that a 326 engine would be a sweet engine, as BigK & Firko indicate on the old posting. I would think it would be even better w the radialfin engine like BigK's than in the factory-done squarebarrel engine. (No offence Mark, just a later design)
Later 320 Maicos actually used a 76mm piston, not 77, but its close. Those 320's were said to be very fast too.
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i think keith stacker built that engine from memory
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Can anyone check what he did? (If he gives away his secrets)
My guess is he started w a blank sleeve.
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isinit all ready on this post /or the original post . and it not there i remember asking him last time so when i go over there this week i will ask again ,
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if you See Keith Stacker Paul, ask if he ever put a Honda top end (4 stroke) on a Maico bottom end? someone once told me this years ago but i think it may have been a myth as thats a lot of engineering to run cam gear, oil feeds etc.
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well i will ask him but if he burst out laughing and calls me a idiot i know ive been set up a beauty .but any thing is possable
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it was probably more likely a honda engine transplant into a Maico frame i reckon as thats possible.
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Paul,
I think the last 326 post in Jan ended w you saying you were going over to stackers & would ask, but I don't think the answer was ever posted.
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mmmmmmmm ok iwill ask again :P sorry im a tad late with the answer
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Ive got Keiths Stackers or what im told was keiths old 250 square barrell in the shed although havent had the need to pull it down yet, gotta say though its got more pull than my 77 AW400 so will be interesting to see what has been done when i get a chance to pull the top off at the end of this season, (although i aint telling anyone ;D) Kieth Stackers old 400 square barrel was for sale on ebay a while back as well when i bought the 250 and didnt get a bid at 5200 off memory and it was immacualte and had been ported etc by keiths son so i was told, bloke who was selling the bike was bloke from Victoria named Alan and sure he still has it, it would be one nice bike to get a hold of 8)
Sorry that was a bit off topic, just felt the need to say it ::)
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hoony, keith did graft a honda topend
onto a maico bottom end
and keith makes all the sleeves he can do them from scratch
but i am not sure if he is still doing them
and i dont think paul is doing them ???
paul can ask and get back to us ;D
and he did transplant a honda engine in a maico frame
it was his trail bike ;D
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holeshot, keith is still doing sleeves he did one for my mega 2
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hoony, keith did graft a honda topend
onto a maico bottom end
and keith makes all the sleeves he can do them from scratch
but i am not sure if he is still doing them
and i dont think paul is doing them ???
paul can ask and get back to us ;D
and he did transplant a honda engine in a maico frame
it was his trail bike ;D
well there ya go , thanks Honny's Buddy. wonder if any photo's exist. That could be you mission Paul should you choose to accept it ;)
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i think i have a picture somewhere of the engine
and also the honda/maico will have a look ;D
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Thanks Holeshot & Paul. I tho't he'd be making his own sleeve for the 326.
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I would have thought that fitting a 250 crank to a 400 and skimming 10mm from the base flange of the barrel would have been the easier option to producing a 326. That's how the factory did it.
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this what paul stacker said
hi paul year getting ready packed all weekend
326 is a 250 with a 400 piston in it the barrel is sleeved out to fit
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just came back from stackers and keith was fitting a 490 sleeve to a 76 cases and 400 barrell ,you would nt know it was in there if you get my drift ;)
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but he said rebores were very limited
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Paul,
Next time yr over at Stackers, can you ask him if he leaves the boost port in the 250 barrell for the 326 conversion or removes it when he resleeves it?
Thanks
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sure i rang and hes busy but he said they take 10 ml out the barrell for the sleeve and the boost port isnt that deep so they redo the port (its chinese to me ) so if you want to know any thing in particular
tell me which model were talking exactaly cause from memory in the original thread it was big k 75 model 250
here my email [email protected]
and i will forward it to him and then post the reply im going over tomorrow any way
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Paul,
Did you get my email?
Yes that boost port mod makes sense.
I'd also like to know what he does to the inlet also. Enlarged? Widened? Lowered? How much?
I'm still talking about the early radialfin motor. Esp 73, but 74/75 don't seem to be a lot different.
Many thanks
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yeah i got it and sent a reply apparently the infomation well has dried up and he said send a barrell in and get it done was the last reply (secret maico bisness)
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I recieved the below email from American Maico guru Jim McCabe a number of years ago and only just found it while cleaning up my hard drive files. It's an interesting read, even if you don't totally agree with his theories.
MAICO 326 THEORY
I built a 326cc oval barrel in 1967 using 250 -70mm stroke crank
under a 360 oval barrel cylinder for Enduro work. The 360 oval barrel
with a 76 mm stroke vibrated a lot at higher rpm and the 70 mm stroke
326cc I came up with was much smoother. I was using a tucked in
silencer from a Bultaco Madador on the 360 oval barrel at that point
and it and the 30 mm carb carried right over to the 326cc version
with no change. Compared to my buddies 360 oval barrel I lost a bit
of torque but had another 12-1500 rpm on top and actually the bike
became faster in the woods and definitely had a much faster usuable
cruise speed for Enduros. I recently got my original 326 chassis(62-
65 single loop frame) back after 40 years complete with the engine
etc. to restore.
I purchased a factory made 326cc radial top end a few years ago, with
the 70mm stroke, but with a 250 pattern rear boost port inconjunction
with 77 mm bore. I've done a bit of research on various combinations
of 400,440 and 501 engines. Incidently the original 360 oval barrel
cylinder required decking the top of the cylinder and also the top of
the crank case by 1/2 the stroke decrease (3mm off each) to get the
proper degrees of timing. The key to any of these mods is measurement
of the port locations in the cylinder castings to see if the finished
port timings are close to optimum. Perhaps the most interesting swap
is conversion of a 501 back to approximately 460cc via a 250 stroke
crank. Yamaha rods with longer center distance can be employed to
reduce the machining required in some cases, and late model cranks
can be destroked to provide the advanges of 3 row primarys.
Incidently I dropped off a 80+ pound block of aluminum for my brother
to start machining on a 760cc. McCabe top end. 108mm bore planned.
Within limits, I believe bore and stroke relationships are less
important as far as power characteristics/max power than the port
timing and the exhaust expansion chamber of the engine being built.
The biggest advantage of the short stroke versions is they usually
have larger transfer passages (in proportion to displacement) than
the original smaller cylinders and are capable of breathing better on
top end in addition to the increased displacement. Power output is
controlled really by how many cfm can be flowed per minute and the
shorter strokes will allow higher rpm thus more strokes/minute within
which to flow fuel and air.(and many of the destroked engines have
wilder port timing than the original cylinders had) In the past 50
years the biggest change in Maico engines is in increased vertical
transfer port areas. The difference in actual exhaust port areas
between a 68 250 square barrel and a 2000 water cooled power valve
250 is actually not that much but the transfer ports have doubled in
area during that period. My long term rule is to optimise the
transfer port areas for better breathing and more top end power.
(440's in particularlar need increased area as the increase in bore
dia. is obtained by a reduction in transfer port area) All that said,
a longer stroke combined with a shorter (percentage rod
length/stroke) rod will provide better low speed punch than a short
stroke version of the same displacement in my limited experience.
Nothing beats porting cylinders area wise and degree wise for the
rpm/power characterists desired using data available to us today.
Expansion chambers are another matter however and I'm planning on an
inertia type dyno to facilitate tuning of my engines more accurately.
Some of the 370 Suzuki Savages had very violent power characteristics as
well. I believe there was eventually found a solution to some of the
violence thru the use of an altered ignition advance cure. The best
example of over square under square engines power output I'm
experienced with, is the 125 thru 350 Bultacos where the 125 despite
it's long stroke was a very sucessful high out put engine while the
350 short stroke Astro's are also very very competitive. And the 350
singles went very well on Road racing as well. I firmly believe it's
port timing/expansion chamber design that's the predominant
contolling factor, although most 250 motocross 2 stokes became
slighter under square (strokes became longer) in recent years. I have
to admit that my 499 has grown to be some what of a light switch
engine as far as how it hits compared to power delivery of a stock
400/440/490. as I've strived for more top end output.---
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Thats very interesting from one who has a lot of runs on the board w Maicos (ie Jim McCabe). Also interesting to see that the factory did produce a radial-fin version based on the 250 boost-port barrell.
While it would be difficult to go past a more-or-less 'proven product' like Keith Stackers version of the 326 if one wanted to go the 326 route, its worth throwing in a few other ideas. Maybe its a bit abstruse/esoteric, but then we do well to have theory push the boundaries of practice. Perhaps there's a 'better mousetrap' around the corner!
The limitation as I see it is the boost-port/Inlet strangulation. Its bad enough on the 250 - how much more so on a 326 version. With a larger dia piston, the IN port can of course also be widened if there's enough meat in the barrell (which there appears to be), but would it be sufficient to let the 326 breath to its full potential?
It would be tempting to remove the boost port when making the 326 sleeve, then remove the boost port casting in the IN tract & widen the TRs to compensatee & give sufficient TR time-area for 326cc. There appears to be enough room to do so (w/out having the TRs too close to the EX), & enough meat in the TR castings. (You lose about 1mm in ht - which aint a bad thing on this engine - but gain about 1mm in width in all the TRs just by boring for a larger piston/sleeve.)
That would give a nice unobstructed IN port, & perhaps an even better 326 version. But you're still limited by 326cc, which is kind of no-man's land.
I vaguely recalled that the factory experimented w a "revvier" 352cc GP engine in the 70's. Yesterday I found that (brief) article. It was in 74. Weil commented that it had about the same peak power (as the long-stroke 386cc '400'), but vibrated less & was "easier to ride".
My guess is that it was an 80x70 engine (which is exactly 352cc) probably using a 250 crank, & the pic showed the shorter 7fin barrell on the bike. Obviously the factory never developed that engine to production. Not surprising since most of a small factory's limited development resources were in suspension at the time, & other major competitors were increasing capacity not reducing it.
I can't help wondering tho what might have been if they'd used the 82mm 440 piston w a 70mm stroke. That would have given 370cc, almost 20cc more than the 352 & perhaps more competitive at the time.
And thats a conversion worth considering, as Jim McCabe suggested above. LA Sleeve's 82mm 'blank' sleeves are only 86.6mm OD - just a fraction more than the spigot in the 250 cases.
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Actually, having checked LA Sleeve's catalogue, its the 80mm bore blank sleeve thats 86.4mm OD. The 82mm bore blank sleeve's OD is 88.4mm (My memory aint always what it used to be)
Here's a few tho'ts on using a 400/440 barrell & head on 250 bot end - just floating ideas.
Apparently the 73-74 250 rod is 5.5mm shorter than 400's while piston deck hts are the same. So w the 400 engine having a 13mm longer stroke, if you bolt a 400/440 barrell & piston on the 250, the bot of the Ex/Tr ports is about 1mm below the piston-top at BDC but the top of the cyl/sleeve is 12mm above the piston-top at TDC. (The 400 barrell appears to be about 12mm taller than the 250's). Which of course is useless & the port timing is ridiculous.
Now if you can drop the barrell 4mm (by machining bot of barrel &/or top of cases), based on the 400 SQUARE-BARRELL port hts, the EX & TR timing are very nice for a big-bore (c 89.5deg & 117.5deg ATDC) tho IN is a little shy (c 74deg BTDC) w an 82mm skirt. Incidently, that is almost identical to KX400 timing (except IN is 76deg).
However you still have 8mm above piston at TDC. Somehow you would have to lower yr head about 8mm, perhaps by machining some off the top of the sleeve (w/out removing all the top flange of the sleeve) & some from the bot of the 400 head (if there's enough meat there) so that the combustion chamber sits down inside the top of the cylinder like the 501 & 250 Canam.
Or make a new liner to suit & machine 8mm from top of barrell (which could remove the top fin). If you did that, it would be tempting to consider using a 440 piston & a thin-wall sleeve in a 400 barrell machined to suit. Jim McCabe mentioned that the std 440 Maico is a bit restricted in the transfers, but it may be fine for 370cc which is what 82 bore x 70 stroke makes.
Of course, you may have to rebalance the crank & adjust the volume of the combustion chamber too.
Wonder if someone (like Jim McCabe) has already done it.
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ive been in formed that one off the stacker 326 barrells and head are in with all the ,maico parts i bought .
;Dtheres another one there ill have a look .what should it measure
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Paul,
I'd be very interested to know the width & depth of the inlet port if you have a 326 barrell there.
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not here yet
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Looks to me like std 250 cylinder Paul. Is it 67mm bore?
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yep so then its not what i was told ,sorry i carnt help cause that what i was led to belive when it was sent ,the mystery continues
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Paul,
It maybe the 'Stacker-modified 250'. It supposedly used a Magnum piston & had some machining done to the barrell/head.
Is the top of the ring 2-3mm down from the top edge of the piston? (Magnum pistons were)
Also an you measure the ht of the barrell from base-gasket surface to top of liner?
(I ask this cos it may have been machined so as to 'drop' the barrell & retard Ex/Tr timing. This should identify if anything 'trick' has been done to it)
Thanks
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from the base gasket to the top of the liner is 133 mm
the head has notches in the top were it was held in a lathe and the piston ring is at the top /l shaped ring
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(http://i382.photobucket.com/albums/oo263/ozmaico/IMGP2141.jpg)
(http://i382.photobucket.com/albums/oo263/ozmaico/IMGP2130-1.jpg)
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Hmm, thats std ht for the barrell. I'd say he just milled the head (by the look of the pics) to raise Comp Ratio. Piston appears to be regular 250 piston.
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P,
Can you check the deck ht of the piston pls - top of gudgeon to top of ring.
Also, does it have round hole or oblong hole in the back of the piston for the boost port?
Thanks