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Mazda 12A balancing

 
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jsd454



Joined: 29 Jul 2005
Posts: 5

PostPosted: Fri Jul 29, 2005 9:35 pm    Post subject: Mazda 12A balancing Reply with quote

I am curious as to how many of the board members have any
knowledge of rotary engine balancing. Specificly I am
putting together a "hybrid" 12a (81-82 counterweight /
flywheel and 83-85 rotors.) My questions are:

Does anyone who has done this know how much weight was
removed from their counterweight and flywheel to acheive
balance with the lighter rotors? If so, this will help me
determine roughly how far off we are which seems to be a LOT!

When balancing, do the bob weights simply equal the weight of
the rotor assembly (incl. seals, springs, oil etc)? I am
aware of the offset required on the eccentric journals
towards the gear sides to match the weight distribution of
the rotor, but is there anything else? Bob weight rotational
orientation?

All help is appreciated. I am just trying to wrap my head
around these nifty little engines!

Thanks!
Jeff
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jsd454



Joined: 29 Jul 2005
Posts: 5

PostPosted: Wed Aug 03, 2005 6:44 am    Post subject: Reply with quote

??? 138 views and no replies??
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Jingyee
Site Admin


Joined: 11 Jul 2005
Posts: 85
Location: Portland, OR

PostPosted: Wed Aug 03, 2005 11:31 am    Post subject: Reply with quote

jsd454, I'll get some information for you today.
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Blake
Been there, done that


Joined: 12 Jul 2005
Posts: 135
Location: Portland, OR

PostPosted: Wed Aug 03, 2005 6:20 pm    Post subject: Reply with quote

I'm going to have to ask Rob on the specifics of your particular combo. He's gone for the day, but hopefully I can ask him tomorrow before I take off for a long weekend in Seattle. As to the more general question about balancing, I refer you to the following two pages from Rotary Engine by Kenichi Yamamoto, copyright 1969.




Hope that helps.
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Blake Qualley
Pineapple Racing, Inc.
(503) 233-3878
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jsd454



Joined: 29 Jul 2005
Posts: 5

PostPosted: Wed Aug 03, 2005 9:12 pm    Post subject: Reply with quote

Blake-

Thank you very much! Unfortunately, I already have that book. It really does have some great information! I do appreciate you taking the time to post those pages!

So, that equation tells me that there is no special consideration to the shape or movement of the rotor. It also appears that the mass center of the rotor is equal to the eccentricity of the eccentric shaft. Is that correct?

If so, would the standard bob weights used to balance a piston engine work assuming that the mass was evenly distributed on both sides and that they were both oriented the same?

I have also seen this tech article by Mazda Motorsports.

http://www.mazdamotorsports.com/webapp/wcs/stores/servlet/Tech?storeId=10001&subject=balancing

It makes no mention to the type or shape of bob weight used. I have spoken with two people there that only referred me to some other shops that do balance work which have been little help. It also appears that the bob weight values given are for the competition rotors and slightly higher than the stock 83-85 rotor weight.

I am confused as to why we are not able to balance this thing. I should also say that I do not have any hands on experience in engine balancing. I am trying to have a local shop do the work who does have appreciable experience with piston engines and nice equipment (Sunnen dcb2000), but no experience with rotary engines yet.

Thanks again!
Jeff
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Blake
Been there, done that


Joined: 12 Jul 2005
Posts: 135
Location: Portland, OR

PostPosted: Wed Aug 03, 2005 10:46 pm    Post subject: Reply with quote

jsd454 wrote:
So, that equation tells me that there is no special consideration to the shape or movement of the rotor. It also appears that the mass center of the rotor is equal to the eccentricity of the eccentric shaft. Is that correct?


Yes, exactly. The rotor mass is centered on the E-shaft journal, which corresponds to eccentricity.

Quote:
If so, would the standard bob weights used to balance a piston engine work assuming that the mass was evenly distributed on both sides and that they were both oriented the same?

I have also seen this tech article by Mazda Motorsports.

http://www.mazdamotorsports.com/webapp/wcs/stores/servlet/Tech?storeId=10001&subject=balancing

It makes no mention to the type or shape of bob weight used. I have spoken with two people there that only referred me to some other shops that do balance work which have been little help. It also appears that the bob weight values given are for the competition rotors and slightly higher than the stock 83-85 rotor weight.

I am confused as to why we are not able to balance this thing. I should also say that I do not have any hands on experience in engine balancing. I am trying to have a local shop do the work who does have appreciable experience with piston engines and nice equipment (Sunnen dcb2000), but no experience with rotary engines yet.

Thanks again!
Jeff


I'll get Rob Golden to help answer this part of the question. He's the engine builder and has extensive experience balancing custom race setups. I'm just the parts guy. Smile
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Blake Qualley
Pineapple Racing, Inc.
(503) 233-3878
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Blake
Been there, done that


Joined: 12 Jul 2005
Posts: 135
Location: Portland, OR

PostPosted: Thu Aug 04, 2005 6:21 pm    Post subject: Reply with quote

Rob said it was not anything special. He suggested you use the 83-85 front counterweight because there's no point in doing extra work. He also said to use the weight of the rotors, with bearings (~250 grams), plus an additional 250 grams for the weight of the seals, springs and oil. At that point, there is absoultely nothing special, so if you continue to have problems you may want to try someone else to do the balancing.
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Blake Qualley
Pineapple Racing, Inc.
(503) 233-3878
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jsd454



Joined: 29 Jul 2005
Posts: 5

PostPosted: Thu Aug 04, 2005 9:00 pm    Post subject: Reply with quote

Thanks Blake! I will give them another shot and see if they can make it right. Thanks for the tip on the counterweight! That makes sense. I suppose it looked smaller, but in retrospect it is going to end up the same either way after it is matched to the rotors.

I will keep you posted!

Jeff
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