The humble 250 Maico

[JC]

Just following up on some comments on the humble 70s 250 Maico in other posts.

No doubt a VR, Phantom, Pursang, 'snore etc would out-drag it, but they weren't too far off the pace. I do recall that I often got holeshots on my 73 bike in 74 as did other maico pilots in the region, but we weren't national calibre.

In Oct 75, DirtBike printed a copy of the factory modification bulletin recommending porting changes to Ex & Inlet. Ex to be 37mm from top of liner, 58mm wide at top (above transfers) & 52mm wide at bottom. Inlet to be 113mm from top of liner & 52mm wide. Barrels stamped later than June 75 were said to have these specs.

I recently measured 2 barrells from 73 & 74 & both were almost exactly that in heights (didn't check widths), but I don't know if they were stock or not (didn't look all that closely at the time). Transfers were 52mm from top of liner.

That translates to Ex opening about 86.5deg ATDC & transfers opening at about 113deg ATDC for durations of 187deg & 134deg respectively, both of which are rather radical/advanced. Bridged Ex & transfer ports (4 of, plus boost port) are rather large, taking advantage of the benefits of a long-stroke motor. Whether you go on total duration or time-area they're rather hot specs.

So why were they off the pace at the poity end?

Lozza says he gets better performance out of unbridged exhausts & I don't doubt him, but lets stick w the bridged port.

I suggest 1) heavy flywheels consume horsepower to spin & to accelarate, & 2) perhaps the main reason, the inlet duration is only about 160deg (w an 80mm piston skirt which I think was std). Not only that but the sizeable boost port tookup some of the inlet port area, so on both duration & time-area the inlet is very mild (which was typical of euro thinking of the day, tho there were some exceptions)

DirtBike claimed the factory experimented w lighter flywheels on the 250 but never went into prod'n w them.

Seems to me that if you want a faster 250 Maico, start on the inlet area/duration, & if yr real serious, turn some weight off the flywheels.

Anyone tried it?

A friend of mine on a very quick 'snore says he was zapped by a 250 Maico at the Dirttrack nats like he was standing still. No doubt there are some quick ones out there.

Anyone got any other tips that aren't top secret?

Mark, you said in another post that yr flouro-orange one was quick. Do you recall what was done to it?

[firko]

John....It was quick for a Maico 250 and a reliable little gem. I'd forgotten about her. It was the only 250 Maico I ever really liked. It was essentially stock except for some slight combustion chamber reshaping to alter the swish area and slightly raise the compression, all of the ports were matched but the port timing and widths weren't changed. I had a Peter Reynolds tapered header pipe, almost the same as that currently on my 350. The ignition was stock points using stock timing and the clutch was from an '80 250. I ran that bike on methanol. I mainly used it for dirt track but I rode her in the occasional  motocross and it was a good reliable old bus. I sold it to Barry Collyer who won a lot of races on her until she was destroyed in a garage fire.

My next radial 250 was built from parts using the frame from my spare Maico 350 square barrel, the left over purple anodized wheels and forks from my 440 and a new, almost unused 250 engine I obtained from a bloke who'd bought a new '74 250 and immediately removed the engine and fitted it to an Elstar slider frame. He found it too slow after only one ride and then bought a second hand 440 engine and put the 250 under the bench where it laid for 25 years until I bought it for $500. I basically had Peter Reynolds do the same head mods to it that he'd done to my earlier 250 but left the ports alone, I didn't even blueprint them. I fitted a 38mm Bing from a Husky, and a 490 clutch. Everything else was stock. As I reported elsewhere on this forum we decided to go all out for the '99 DT Nats at Nepean and put the bike on the dyno for three solid days (it was sponsored). With a fresh engine appearing to run well we achieved an underwhelming 17bhp with the stock pipe and carb. After using six pipes and four carb setups and countless jet changes we finally got 27bhp using VP race fuel and the 38mm Bing and a genuine period Wheelsmith pipe I'd had since the day. After all of that fiddling and with race fuel and a bigger carb and trick pipe we finally achieved  the factories advertised HP figures. Nonethless, the bike was super quick on the Saturday easily winning the first round over Peter Lee and his 40+hp methanol Elsinore. On Sunday the bike seemed to be a little less perky but Chris Ellis on board her won round two, again from Peter Lee. Unfortunately, in the final round the bike was way down on horsepower and Chris could only manage fourth on a rapidly slowing bike after leading for two laps, relegating him and the bike to second place in the championship. Afterwards we'd discovered a blown base gasket, a pulled barrell stud, and a very cooked piston.

All of this proved to me that Maico bullshitted with horsepower figures for the 250 as we had to really work hard with many an expert twiddling the spanners and flog the living daylights out of the bike to get anything near the performance advertised.  A few weeks later we went to Griffith for the NSW titles with the bike on methanol Chris won the over 30 class and 2nd place in the 250 all in class and I came third in the over 40 250 class on her. I recently gave the engine to Les Richters.

[HuskyPete]

Firko, forget the Maicos, you should have raced a Husky 250 mag they had over 27.5 HP standard. My 250 Mag dyno chart.

[firko]

Pete.....The Maico was supposed to have 27hp stock but you and I both know that a Mag 250 Husky will blitz a 250 Maico, all things being equal. I've misplaced my dyno charts, I think they may have got ruined when my garage flooded although I know one sheet survived for sure. Now all I have to do is find the bugger.

[JC]

Mark,

How was the dyno driven from yr 250 in those tests? Off the crankshaft sprocket, off the countershaft sprocket, or w the tyre on rollers? (It makes a considerable difference)

Likewise Pete, for yr MAG dyno test?

Many different people put the radial-fin Maico on the dyno back in the day & published them in the magazines of the day, & they regularly made 27hp on the same dyno other 250's made 28-30hp (probably measured at the countershaft sprocket), tho conditions may not have been exactly the same.

That is the key in comparing hp of different engines - they need to be compared on the same dyno under the same conditions if possible or its all-but useless for comparison.

Interestingly DirtBike put a 250 squarebarrel motor on a dyno to test a whole lot of fuel additives back in 72, driving the dyno off the crankshaft sprocket & consistently got 31HP at the crank!! (even w'out the additives) OF course the factory claimed 36HP at the crank as I recall (for both it & the radialfin engine - but I believe the latter had much more advanced porting. Go figure!).  Even w the factory bulletin specs of 75 they still claimed, you guessed it, 36HP "on the friendly factory dyno" (to quote DB's facetious wag who wrote it up).

Occasionally someone measured rear-wheel hp (presumably driving the dyno thro the rear wheel on rollers) & the Maico only managed 17hp. The same magazine measured a 73VR at 22.5hp, a 73 Husky (not a Mag) at 17.5hp, a 73 Kaw F11M at almost 21hp (& a 73 400CZ at nearly 24hp, a 450 kaw at only 25hp & 73 MX125 yam at 10.5hp).

That begins to tell more of the story - akin to what yr saying Mark. (Altho, had that Maico not blown a base gasket etc, presumably it would have beaten that worked-over 'snore. I wonder what the 'snore would have produced on the same dyno)

But its the torque figures that tell me the story - the Hus & Kaw have 35% more torque than the Maico & the VR has 40% more. (HP is just a mathematical calculation from torque & rpm.) Interestingly the 450 Kaw has twice the torque & 400CZ nearly twice the torque of the 250 Maico, as you would expect.

Torque is largely related to volumetric efficiency - how much fuel-air mixture you can consistently get into the cylinder to ignite, tho there are other factors like comp ratio. Boyesen notably says, HP is directly proportinal to how much mixture you can get in there, & his whole reedvalve business is built on that.  Seems to me he's right.

Which brings me back to the Maico's main limitation being the low duration/time-area on the inlet. That's its biggest drawback powerwise, tho the power-drain of the heavy flywheels doesn't help. (I'm led to believe that the flywheels are the same as the 400 ones, apart from the shorter throw for shorter stroke).

If I still had one, its the inlet time-area I'd start modifying.

[HuskyPete]

John, we changed the rear tyre for a slick and the readings shown were at the rear wheel. The brand of Dyno is at the top of the sheet.Peter

[firko]

Same here, we used a Pirelli Phantom road tyre I had laying around the garage. The figures are rear wheel, similar to Petes Husky. That 17hp Dirt Bike got backs up our results prior to the fuel, carby and pipe changes. As a matter of interest, Cary L'estrange at Condo had Gary Treadwell do a fairly radical port job and achieved around 40 rear wheel HP on methanol with his '73 250. It was rocket fast but extremely fragile. I believe he still owns it and is hanging up in his bar. Peter Lees Elsinore was a quicky as well and reputed to have well over 40 rear wheel horses. Peter lurks this forum and he may be able to back up or debunk the rumours. It was/is damn quick, that's for sure.

[JC]

Thanks Peter,

Thats a very good reading then. Was that w the std pipe or w yr aftermarket one?

[HuskyPete]

In the dyno test the Mag 250 had a aftermarket pipe from Hotrod Husky in the states, it was designed and made by the Maico guru Eric Cook.

[JC]

One of the limitations of the strap-it-on-the-rollers method, if yr trying to compare one bike to another, is you can't be entirely sure you haven't got any slippage, & if there is some, how much. Slippage means unmeasured HP. Positive connection via chain elimates that variable, but isn't always an option.

I'm not surprised the Treadwell Maico on methanol got around 40hp. Just looking at the porting design of the std transfers & exhaust, which make good use of the advantages in port area of a long-stroke design (like on all modern 250MX engines), I would think you could get over 30 rearwheel Hp quite reliably w work on the inlet & perhaps flywheel lightening.

Best to keep peak revs down on a longstroke engine tho, to avoid excessive mean piston speed which causes unreliability via ring-flutter etc

[Lewo81]

It`s interesting reading things I have tried in the past. I also owned a 250 radial and it was a slug. After a couple of years trying different things I gave up and sold the bike less the broken engine. I had the crank lightened by 10%. Then had spacers made to replace the lost metal in the crank area to maintain a similar crankshaft volume, the result was bearly noticable. The bike accelerated OK but once wound up but lost about 2 bike lenghts out of every corner. A latter 250 of mine now runs the rear transfer which blocks the inlet tract removed and a homemade reed block installed, this bike runs much better. It`s no world beater but at least makes competative power and is much more fun to ride. I`m no expert tuner but my experience has shown the crank lightening not to be useful and efforts put into the inlet port and over-coming the obstruction that the rear transfer creates to be the area that holds the engine back. As has been said the rest of the porting lay-out and timing specs should produce plenty of power but it just doesn`t happen. I tried different pipes, 40mm bing carby which helped, more compression, ignition timing changes,  a second cylinder. Finally gave up in frustration. The only thing I didn`t try was methenol. Just my 2 bobs worth.
Another guy in a nearby town had a crank rebuilt with a shorter rod and I don`t know what mods to go with it, he said not much though. I would have swapped him engines any day of the week, again not the most powerful bike but enough to be competetive and fun to ride. He must think so to as he has owned and raced it for around 10 years now, make what you will of that.

[JC]

Thats very interesting - shows why a discussion like this is so useful on a forum like this. I'm a firm believer in that famous quote - "men are never more likely to settle a matter rightly than when they are allowed to discuss it freely". I would have tho't the lightened crank would have made some small improvement as the std bike revs so slowly (compared to other 250s), but it seems not in that instance. The std engine is a great engine for mud races!

Not surprised yr mods to the inlet/boost port & reed valve worked quite well. Thats to be expected. I'm not up w the differences rod length makes, off the top of my head. I know it changes port timing but I can't recall which way for longer/shorter rod. I tho't longer rod was generally better, as it also gives more crankcase volume like modern bikes, but no doubt there is an optimum length for every engine. And the std Maico rod is already very long, so it maybe already past optimum length for that engine.

There are 2 other important factors worth considering: direction of transfer ports, & combustion chamber design. ie shape & comp ratio (squish bands etc). A lot of the advance in 2 stroke design for power has been achieved in combustion chamber design over the last couple of decades. The factory bulletin printed by DirtBike in 75 raised C.R. but didn't mention shape/squish-bands. I don't have a head in front of me & I don't recall the shape of std combustion chamber, but it may well be that considerable improvement could be made here. (My vague recollections are of a very simple design.)

And transfer port direction is quite critical.

I recall Brad Lewis once telling me about their experiments on one of Daryll's 250's. One barrell was fast, another was a slug & the only difference they could spot was the direction of the transfers. Slug cylinders did seem to be a problem w the 250 engine. The quality control probably wasn't what it should have been. Thats more than likely. Maybe there were more slug cylinders than 'fast' ones. Even the factory guys were said to try different cylinders to get a good one to start with!!

I was always tempted to adapt a Yam 360/400 top-end & piston to my 250 (same stroke), & still would be if I had one today.

Just on the safe upper rpm limit of this long stroke design, 8700rpm equates to the dreaded 4000ft/min mean-piston-speed safe limit for materials of the day. Beyond that, reliability could be expected to taper off fairly quickly. The std 250 engine readily spun to 8000-8500rpm. Not a lot of margin for error, esp once you start modifying.

[holeshot buddy]

just get a 74 vr250 montesa
or a phantom and save yourselves  all the trouble of porting etc
fast on the track and fast standing still

[090]

I dont think there are any good bikes left mister shot. Sounds like you have all of them 

[paul]

heres a gem here brad up your way
http://cgi.ebay.com.au/kawasaki-kx250-1988_W0QQitemZ220272105472QQihZ012QQcategoryZ102690QQssPageNameZWDVWQQrdZ1QQcmdZViewItem