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Author Topic: MARZ 2.5 crankshaft  (Read 247 times)
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Fourfingers
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« on: February 10, 2017, 10:03:25 AM »

Another day, another silly question:
Several folk recommend de-stressing the very hard crankshaft on this motor.  As you know this involves putting with the bread at 230 C for 45 mins .....
Two questions really - is this procedure needed? (I do crash my planes regularly) and
When I remove the shaft the rear ball race seems firmly attached to it.  Doesnt detach easily so didnt want to bash it and possibly deform it.  Assuming crank should be baked, is it OK to leave ball race on?
Any celebrity chefs out there, your opinions are valued.
Thanks
Ff
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gossie
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« Reply #1 on: February 10, 2017, 10:47:20 PM »

Personally I would take the race off.
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Fourfingers
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« Reply #2 on: February 11, 2017, 01:57:32 PM »

Personally I would take the race off.
Thanks Gossie ... a litle gentle heat perhaps to help ease it off?  Not sure how much one can heat a ball race.
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qazimoto
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« Reply #3 on: February 12, 2017, 05:33:28 AM »

Another day, another silly question:
Several folk recommend de-stressing the very hard crankshaft on this motor.  As you know this involves putting with the bread at 230 C for 45 mins .....
Two questions really - is this procedure needed? (I do crash my planes regularly) and
When I remove the shaft the rear ball race seems firmly attached to it.  Doesnt detach easily so didnt want to bash it and possibly deform it.  Assuming crank should be baked, is it OK to leave ball race on?
Any celebrity chefs out there, your opinions are valued.
Thanks
Ff


It sounds like a lose/lose situation to me. Yes you might destroy the ball race if you heat it to 230 C for 45 minutes, particularly if it has a brass or even non metallic cage. There's no easy low risk way to get the race off the shaft if it's stuck. Mostly you replace a race if it has to be pried off. Can you get a replacement race? I've heard of the soaking the crank at 230C treatment but is this necessary for all versions of the Marz? Heat treatment of Steel is an intricate process that's usually performed with some reliable information about the characteristics of the metal. There's a lot of magical thinking concerning HT on the internet. Might be better to leave it as it is, the Marz engines my fellow club members have had haven't broken their shafts, but they all use ignition improver and know how to tune a diesel. If the worst happens  buy another Marz. There's no shortage of 'em.
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Fourfingers
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« Reply #4 on: February 12, 2017, 11:55:45 AM »

Thanks for the latest from Oz.  I was coming round to the same conclusion myself, ie leave well alone ....
Dont put a big prop on it and dont crash!  Simple, job done!
On a different tack, I dont know if its a feature of rear induction, but it seems to have difficuly drinking ..... getting from first fire to steady running takes a lot of exhaust primimg and choking doesnt seem effective.  I did put a thicker gasket on the back plate. Maybe that will help.  We'll see.
ff
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old4570
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« Reply #5 on: February 21, 2017, 05:48:13 AM »

No , do not heat ball bearings ..
This is one item on a engine you dont want to soften ..
A overly hard shaft can break with impact ..

 De stressing ?  Im not sure this is an issue with model airplane engines ..
I can certainly understand slightly softening the shaft to make it a little more pliable ( flexible )

 If your not running ignition improve'r then yes , run a larger prop ..
But if your running ignition improve'r then a 8inch DIA prop should be fine .. 

Are MARS shafts breaking ?  ( I had one but never took it out of the box )   
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Fourfingers
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« Reply #6 on: February 21, 2017, 11:11:49 AM »

Thanks, old chap
Never had a shaft break meself, this being my first MARZ ... Just reading a few blogs on tinternrt that report this.  Could be fake news of course.
I have given up any thought of baking the thing.  You should get your s out the box-man do they go.
Talking of flexible crankshafts an in-law of mine served as engineer in the Australian Navy and had a Napier Deltic in the engine room.  Word was that when they fired up or stopped the crank flexed nearly 180 degrees.  Could be legend, but he didnt usually bullshit me.  Cant ask him now, alas.  RIP, Dusty.
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old4570
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« Reply #7 on: February 21, 2017, 07:07:35 PM »

I purchased the MARZ for VTR but could never get a yay or nay on it being used in VTR  ( Class A )
So I sold it .. ( Way back wow must be around 20 years ago ) Where does the time go ?

 There are a lot of interesting engines out there , but the folks that could give the nod ( ? )  , Not to worry !

 I may buy another MARZ , as I have purchased a few interesting russian 2.5cc diesels and I may buy a few more this year ..
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