'81 250 & 490 cylinders

[Husky500evo]

After reading the conversation about 490 cylinders fitting on 250 cases in general chat , I decided to try a little experiment. As I have  '81 MC250 , GS250 & MC490 motors on my workbench with the top ends off, I tried swapping cylinders. The 490 cylinder does in fact fit straight on the 250 cases, which surprised me as I always thought the same as Maico 31. I only things that I can think of to explain the difference in Maico 31's stud pattern is that his motor is an '80 model or is a real early '81 GS 250 that used left over parts from 1980. The '81 250 cylinders have a reed valve of course.

[paul]

 i spoke to john caldwell from canadian maico last week he said no problem useing 250  cases with the larger top end  he sent me a list off  parts  that i would need to do it

[firko]

It just goes to show that you're never too old to learn new tricks. I've owned Maicos continuously, without a break since 1970 and thought I'd heard it all. This revelation showcases the good side of the forum system. The exchanges of knowledge and information via the forum are enlightening and extremely informative. When used properly a forum can be as important a tool as a restorer/builder can have.
This situation raises the idea that it'd be a good idea for someone to collate the various different Maico barrel spacings to see just what is interchangable and what's not. With the rising prices of open class Maicos making it inevitable that they may soon be out of the reach of the average owner, it may encourage some to convert 250s to 326,490 or even 501cc machines.     

[firko]

I just got these pics from Maico490t who has asked me to resize and post them.
 Dave says "The pics I took are of a 82 GS 490 reed barrel on a set of 81 MC 250 cases Engine number prefix MT350. The same barrel dropped straight onto an 82 GS 250 set of cases. Interestingly in the second shot not only can you get a laugh from the piston size but if you look down you can see the two halves of the crankcase stuffers and the end of the rubber 'O' section compression seal - I tried to post these but the site said the files were too big so your help would as always be appreciated" Like I said before, you learn something every day.

[Maico31]

Sorry maicomc490t it looks like you were right. I think the 250 bottom end i was looking at is an '80 model which appears to be different to the '81.

[maicomc490t]

G'day again, and thanks for posting the pics for me Mark - as always a great help.

Glad to help out with the info Maico31 - main thing is it shows guys that there other cheaper options of getting onto a race track aboard an 81 Maico via the GS conversion route and for money the sensible option if you can't afford a real one.

What I would like to now work out is if anyone can contribute additional info regarding how the converted bikes can be expected to deliver eg an 82 490 top end on a 250 enduro bottom end (82 barrels are still fairly common but be aware that once you get the elbow off the intake spigot - by CAREFULLY expanding it with a cold chisel they literally fall off - the spigot diameter is bigger than an 81 and it will need to be machined which I am yet to do, or a rubber carb mount is needed)

As Firko said it will be an interesting exercise to thrash out all the options - Primary and secondary gearing come to mind for starters and then lets look at cutting all the GS stuff of what would no doubt have been MC frames to begin with anyway (at least in theory) which always gets some people hot under the collar - sort of vandalism to some but to me a way to an MC by stealth.

See you all at the back of the pack !!!

[Husky500evo]

Another interesting thing that someone told me , but I am yet to verify, is that an '81 GS 250 has the same transmission ratios as a MC490. Obviously the primary drive ratio is different. I know that the GS250 motor is not that well suited to motocross because there seems to be too wide a gap between 3rd & 4th (& 4th & 5th) . It seems to go from revving hard in 3rd to almost bogging in 4th, especially if you are going uphill. This spread in ratios wouldn't trouble the 490 but, as it has plenty of torque to pull it. It wouldn't surprise me if the gears were the same ,as Maico seemed to be pretty much into interchangeability of parts.