Maico 490 Head Modifications

[firko]

Rather ironic that with the Aprilia GP program had 100 staff headed up by the worlds greatest two stroke tuner (Jan Thiel) with 2 dynos testing 5 cylinder and head designs for 5 days a week for 13 years settled with a head design like the one on the left above. Jan even thought that head was 10 years ahead of it's time and the design probably came from legend German tuner Jorg Muller.

Maico has used that head design since 1978 and it was a noticeable improvement over the previous more traditional design. I think the 'key' to the RK Tek design is the 'sunburst grooves' machined into the combustion chamber. I'm not doubting the brilliance of Jan Thiel or Jorg Muller but I'm prepared to try somebody else's new idea. If it works, my bike benefits and I've learned something. If it's a failure, I put it down to experience and go back to what I used before. The word on the street is that the RK Tek system is beneficial so why not give them a go? http://www.2strokeheads.com/

I had Peter Reynolds do a similar head (without the flues) for my DT1 from Hell many years ago and it, and a piston crown mod made a 2 bike length difference in acceleration and noticeably improved the bikes tractability. I still have a welded up head here that was going to be the Mk2 version. If the Maico conversion is successful I may well send the Yamaha head to RK Tek.

[flyingdg]

http://www.dootalk.com/foru Ams/topic/221983-rk-tek-back-to-back-head-test-vs-stock/

Here is a link to a snowmobile forum that is talking about the RK tek head. All I can say is I've had them recut some of my heads and they work good. The maico head, RM465 and RM500 worked the best of them all that I've had done. I had a 84 RM250 head recut and it worked better just not night and day like the Maico and big RM's. I'm rebuilding a hodaka 125 wombat to ride from Utah to Athena Or. for hodaka days and have a Carabella 125 welded up that RK Tek is going to recut to run on the wombat. I'm 100% sold on the RK Tek head mod. DG

[firko]

I can't get the link to work Doug.

[flyingdg]

I don't know why it doesn't work. I did a google search for (snowmobile challenge RK Tek) and that is how I found the forum talking about some testing that was done on there heads. DG

[Tahitian_Red]

http://www.dootalk.com/forums/topic/221983-rk-tek-back-to-back-head-test-vs-stock/

[Lozza]

Rather ironic that with the Aprilia GP program had 100 staff headed up by the worlds greatest two stroke tuner (Jan Thiel) with 2 dynos testing 5 cylinder and head designs for 5 days a week for 13 years settled with a head design like the one on the left above. Jan even thought that head was 10 years ahead of it's time and the design probably came from legend German tuner Jorg Muller.

Maico has used that head design since 1978 and it was a noticeable improvement over the previous more traditional design. I think the 'key' to the RK Tek design is the 'sunburst grooves' machined into the combustion chamber. I'm not doubting the brilliance of Jan Thiel or Jorg Muller but I'm prepared to try somebody else's new idea. If it works, my bike benefits and I've learned something. If it's a failure, I put it down to experience and go back to what I used before. The word on the street is that the RK Tek system is beneficial so why not give them a go? http://www.2strokeheads.com/

I had Peter Reynolds do a similar head (without the flues) for my DT1 from Hell many years ago and it, and a piston crown mod made a 2 bike length difference in acceleration and noticeably improved the bikes tractability. I still have a welded up head here that was going to be the Mk2 version. If the Maico conversion is successful I may well send the Yamaha head to RK Tek.

Jan Thiel has 25 or 26 world titles to his credit. There has not been an objective test only owners say so. The function of a squish band is to create turbulence the radial lines won't make any more of that. The narrower squish will let the engine rev easier.

[FritzG]

I had RK do the head on my 81 490 after riding with their mod on my 74, 440 radial. The bike seems to pull cleaner and longer from bottom through the midrange with more than plenty eye watering rev on the top end. If you look at all the modern 2 stroke mx bikes they all seem to agree that this type of dome and squish band arrangement is the most efficient way to compress, ignite and burn a 2 stroke mixture. I'm not sure what the physics of the flutes are but Kelsey at RK Teach told me of all the 2 stroke head designs they tested while working with a university on clean burn 2 stroke development this was the best head design they had. I think it's a combination of the most efficient head design, including the proper squish band width and clearance as well as the compression ratio set up for the fuel you run. The top hat Maico head design is certainly better than the double plug radial design (I ran a 1980 440 head on my 440 radial before going to the RK head) and this is the next step up from that.

I feel it was money well spent, it makes the 81 490 just that much better than it already is.

Fritz