mhr rep *Tuning*

[Big B NRG]

There isn't a rule of thumb for exhaustport timing - RPM.

In general the rule is, the higher the exhaustport timing, the higher the RPM, but this doesn't have to mean you get more power.

I can tune 2 cylinders; 1 with 200 degree exhaustport timing, the other with 195 degree exhaustport timing, both doing the same RPM, but one cylinder giving more HP at that RPM then the other. It depends on to much factors.

We can give you an indication; but it won't give any garantees. Post your stock timings for all transfers.

 

[narx]

If you already have a motor + flexible shaft, I think it wasn't' necessary to buy a new kit for a handpiece.

For example I have a simple Ferm 135W machine with it's own flexible shaft. I cut of the fix straight (plastic housing) handpiece and made an adaptor for the Foredom quick change handpieces. I made the adaptor from aluminium and I inserted two small ball bearings too, so it's industrial quality, reliable and cheap solution. I use a Proxxon pedal so the kit is complete.

Hey Browni, could you post some pics of it?

 

[Browni]

Hey Browni, could you post some pics of it?

Currently I haven't got any pictures, but tomorrow I'll make some photoes!

 

[50cczip racer]

have recently tried a pro race 70 pipe and c21 on a standard mhr rep cylinder with standard ignition and 21mm carb and got a surprise result on both power was around 11,500 rpm and between 14 and 15 bhp when set up
i once measured up a cylinder and from memory was approx 189 ex 129 tr so very nice set up for fast road use or add another 3 to 4 degrees to exhaust and leave transfers for a bit more power you can quickly calc this out on kartweb.com port timing calculator

 

[adas]

Aloha, there is a very inexpensive "air pencil" 1/8 inch grinder that does 56,000rpm. It would be great to make an angle piece for it. See it here;
http://cgi.ebay.com/ebaymotors/NEW-...002QQitemZ120206462564QQrdZ1QQsspagenameZWDVW



frank

 

[hac]

have recently tried a pro race 70 pipe and c21 on a standard mhr rep cylinder with standard ignition and 21mm carb and got a surprise result on both power was around 11,500 rpm and between 14 and 15 bhp when set up
i once measured up a cylinder and from memory was approx 189 ex 129 tr so very nice set up for fast road use or add another 3 to 4 degrees to exhaust and leave transfers for a bit more power you can quickly calc this out on kartweb.com port timing calculator

nice to hear that,my MHR replica 128/198 tuned on peugeot bloks,19 carb and TP Nardo exhaust for last seasone is very good ,pull strong around 11400 rpm vith good overreve to 12 500 rpm on top speed.........my plan for this season is MHR replica cyl +1 ring piston with some more work to meching EVO 6 exhaust from pia.
plan is testing this combo with ori Keihin PWK 28 carb and V force 3 from mina......what you gays think about that setup.........?

 

[Big B NRG]

Your BD is 35 degree. Raise your transfers a couple degree to lower your BD. While your at it, angle the transfers upwards.

With a blowdown of 35 degree, your 19mm carb is to small. Fitting a 28 carb is a must.

 

[hac]

i have Keihin PWK 28 mm karb to fit on new setup......my aux exaust port are lower then main ....aux/main 192/198 averige 195°,i plan to rise tranfers on 131°...132°....whot is the beter raising primary transfers only or bouth primary & sekundary tranfers ?

.....thenx for help Big B

 

[Big B NRG]

Get a staged transfer timing. So 132 degree on the primary transfer and 130 on the second.

Also raise your aux. port to 198 degree. Gives a stronger pulse, with more (peak)power, since you can adjust your scooter on 1 given rpm, you will gain power over the complete powercurve.

Don't forget to alter the rooftop angles on your transfers (more towards the head), that quite important!

 

[hac]

OK,I understand......thenx for advice,i work with a dremel but with patience i can fix the tranfers and aux ports......

 

[Rage]

If you already have a motor + flexible shaft, I think it wasn't' necessary to buy a new kit for a handpiece.

For example I have a simple Ferm 135W machine with it's own flexible shaft. I cut of the fix straight (plastic housing) handpiece and made an adaptor for the Foredom quick change handpieces. I made the adaptor from aluminium and I inserted two small ball bearings too, so it's industrial quality, reliable and cheap solution. I use a Proxxon pedal so the kit is complete.

Cheers...

 

[Browni]

Aloha, there is a very inexpensive "air pencil" 1/8 inch grinder that does 56,000rpm. It would be great to make an angle piece for it. See it here;
http://cgi.ebay.com/ebaymotors/NEW-...002QQitemZ120206462564QQrdZ1QQsspagenameZWDVW



frank

I have the very same (brand: Erba Air) air turbine (cost the same here in Europe and the price containing a plastic holder+automatic lubrication chamber aluminium oxide heads)-
However it needs too much air, so you have to buy an expensive high capacity compressor too... My little tiny compressor always work if I use it. But it' s a small and light straight grinder!

 

[Browni]

Hey Browni, could you post some pics of it?

As I promised, here are the pictures. Sorry yesterday I wrote I made it from alu, but I made it from steel. The spring at the end of shaft is original.
[IR]http://mbk.tar.hu/Ferm/shaft1.jpg[/IR]

For the other pictures I inserted links:
Pic2
Pic3
Pic4
Pic5
Pic6
Pic7

The adaptor contains two 4x8x2,5 mm ball bearings.

 

[narx]

Thanks, great idea, looks very nice. Where did you buy your foredom handpiece, all I found was in the US.

 

[Browni]

Thanks, great idea, looks very nice. Where did you buy your foredom handpiece, all I found was in the US.

I bought from the USA (ebay.com). It's wasn't expensive.

 

[hac]

Aloha, there is a very inexpensive "air pencil" 1/8 inch grinder that does 56,000rpm. It would be great to make an angle piece for it. See it here;
http://cgi.ebay.com/ebaymotors/NEW-...002QQitemZ120206462564QQrdZ1QQsspagenameZWDVW



frank

i found this grinder in local shop today ,price is 30 euro,looks very good,specely on that price

 

[McScooterson]

Raise the exhaust port 1mm but correct the blowdown, you want all 3 ports opening at the same time with a 1/2mm crescent raise across the lot other than just the first like stock, widen the 2 side ports by around 1-2mm and finally you want to scrub all the port transfer feeds so there slightly rough. This should give you a nice spread of power. Some of the reps have quite a pointy base to the center port so it may need correction on the bottom edge.

 

[muhuha]

got some measurements

Aux ports -23mm from top
main ex port 22mm from top

distance between aux port and main ex port is 3mm

what tools are used to grind the aux port its quite tricky to get too.

 

[muhuha]

also going on the other 1-2piston ring post shall i keep both piston rings or change to one?


stoke -39.20mm
rod length - 85mm
heights-22mm
duration=206.94

 

[hac]

also going on the other 1-2piston ring post shall i keep both piston rings or change to one?


stoke -39.20mm
rod length - 85mm
heights-22mm
duration=206.94

stock rod lenght on mina is 80 mm,not 85mm,thats whay your calculation is to high.....
if you have 2 ring piston you must put bouth rings on