IS it knackerd?

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goony
Posts: 8
Joined: Mon Sep 09, 2002 3:11 pm
Location: United Kingdom

IS it knackerd?

Post by goony »

HI guys, I,ve got an MDS28 for my combat model and I read the instructions (not the boxed ones) about how to run in a 2st motor by under prping it so it revs high on a rich mixture but I think I cocked it up by using the wrong prop as the only prop i could get was a M/S 8x6 its had 12 onces through it so far but it seems a bit naff as it doesnt seem to want to rev out so where do I go from here?

goony
Lou Melancon
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Post by Lou Melancon »

To the store to get a new one. The prop you would use would be a six inch with relatively low pitch. You would not run rich but instead about 90-95% peak for no more than 30 seconds then shut off and let cool. It should only be warm to the touch. Repeat six times then extend the runs gradually up to a full tank alternating between slightly rich and peak (heat cycle).
goony
Posts: 8
Joined: Mon Sep 09, 2002 3:11 pm
Location: United Kingdom

Post by goony »

I know naff all about metal really AS im a composites guy but if I run it NOW on a lower diameter and pitch wont this still allow the motor to reach its thermal pitch?

goony
Lou Melancon
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Post by Lou Melancon »

Goony,
It depends on the fit of the piston to cylinder when hot. If it still has tight fit when hot you will be ok. It should have a noticeable bump as it goes over the top of its stroke when hot. Not real tight but a noticeable bump.
goony
Posts: 8
Joined: Mon Sep 09, 2002 3:11 pm
Location: United Kingdom

Post by goony »

its still very tight!!! so tight I dont like to turn it over unless priming it but that is when its cold!!!

ill get a 6 inch prop but wot pitch 3?

goony
Lou Melancon
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Post by Lou Melancon »

That will work for break in, but cutting down an 8 or 9 inch diameter prop to six inches is better because they start out beefier around the hubs and have thicker blades. I believe a 4 pitch would be fine for break-in. For flying use a 9X4. That prop won't be as fast on top end but will give you more thrust so that you can accelerate on launch and not slow down in the turns.
goony
Posts: 8
Joined: Mon Sep 09, 2002 3:11 pm
Location: United Kingdom

Post by goony »

ok ive ran it in again!! and it seems OK but what sort of rpm should i be hoping for on a 9x4 or 9x5

goony
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