ausrotaholik

could someone please tell me what compresion sholud be on 12a carby motor, cheers.

12abridgeport

It should be around 90 psi for a good working engine and not than 5-10 psi difference between the chambers.

sweet series ii

i am new to the world of rotaries and i was told that rotaries benifit from having a lower compression whereas a piston engine benifit from higher comp. is this true?
DAVE

Wankelguy

Not really.

ray green

iTrader: (14)

My Haines manual says 6.0 kg/cm2. Funny thing is, I paid $200+ to have a local Mazda dealer check the compression on my 84 GSL (their idea, not mine) and it came back 6.9 kg/cm2 for the front rotor and 6.5 kg/cm2 for the rear. Based on this they said I need a new motor (gag me with a spoon, the car runs great!) I guess the 12A's just get better with age and the Mazda dealer will fix anything that enters their shop, whether it needs it or not.

12abridgeport

you got that right, that's why i never take my car to the mechanic unless there is no other way.

RixRotary7

12abridgeport, what about to a rotary mechanic who ONLY works on rotaries. Would you take your car to him? Also, if you know of any rotary mechanics in the Chicagoland area, drop me a PM please.

Wankelguy

Even taking your car to a "rotary mechanic" can be an iffy proposition. Just about any idiot can build a rotary engine, and lots do. Best to check 'em out thoroughly before letting anyone touch your car.
Mazda dealerships seem to be about the worst.

Rx7carl

105-150 psi is the range Mazda gives.
90 is minimum
And from experience, below 80 will be hard to start and will run weakly, and below 70 wont run.

Thats for stock ports, iron seals. Ported engines and/or one piece carbon apex seals will show lower comp numbers even when new.

12abridgeport

RixRotary7, yeah as Wankleguy sad even the rotary mechanics don't always do a very good job. That is what happened with my 2nd gen, i've had so much money in turbocharging it and the mechanics that did it never got the turbo to work, even worse while during the tune up they broke my o-ring on the rear rotor. And they always had rotary race cars in their shop, so i assumed they knew what they were doing.

PaulFitzwarryne

105-150psi is a huge range, where do theses figures come from? My mechanic, reliable in most matters, says 95-105psi is typical for a 12A in good order which in itself seems a wide range compared with variations in a piston engine.

Rx7carl

From Mazda Paul

Engine Compression
-(1976-85 Engines) Range for earlier
engine will be slightly lower.
-Difference between chambers should
not exceed 20 psi (hot).
105-150 psi @ (HOT)

80-100 psi @ (HOT)
(w/carbon seals)

http://www.mazdamotorsports.com/weba...1&subject=misc

PaulFitzwarryne

RX7carl- thanks for the link to mazdamotorsport. There is certainly some good information on their site. The only trouble is a seem to get an irresistible urge to spend more money each time I come across such available products!