SCCAIT7

Hey guys... finally got around to running a compression test on the race motor... It appears to be about 70lbs...

So what do you do now... I do not know anything about how to rebuild one...

Can someone give me your comments.... This is a race motor...however it is a limited prep (IT-7)... so I cant do anything radical....

Rogue_Wulff

Couple of questions. How was the engine tested. Cold engine, or warm, and what RPM. Premixing or MOP (OMP).
All of these factors make a difference in what to interpret from the numbers.

Kentetsu

Don't give up yet. Before you do anything else, add one can of seafoam to 1/8 tank of gas and run it really hard. If there is a stuck apex seal(s) then this should loosen things up again. Test the compression with the engine warm, and the throttle wide open (ignition disabled). If that doesn't do it for you, then check Atkins rotary for their rebuild video. Well worth the 25 bucks...

trochoid

iTrader: (6)

I remember your posting earlier about your race car being down on power. Even screwing up a compression test, it's hard to get that low of a reading unless it leaked during the test.

Not sure what you are asking here? If compression is down/gone, the engine needs to be opened up to find out why and which parts need replaced. Are you asking about rebuilders, looking for encouragement to rebuild it yourself? More details please. History of the engine, your goals and budget for racing, skills, (i.e. do you want to try the rebuild yourself), etc..

Blake

Get a real compression check before you jump to conclusions. Regardless, you might want to try steam cleaning the engine with water drawn through a vacuum tube. All you need is a 2 liter bottle of water and a long vacuum tube which you will dunk into the bottle as you hold the RPM up with the throttle. The water will be drawn in, turn to steam and scour the carbon out of the engine. You could also just pour it down the carb throat, if that's easier for you. You would be suprised how much water the engine can drink without hydrolocking. Steam is a VERY powerful cleaner and, obviously, contains no chemicals that may be problematic. I've never used Seafoam (the forum miracle product de jour) but I don't like to use chemicals inside the engine unless there is no alternative. Steam cleaning has been used for decades with great success.

Steam cleaning (or the Seafoam, if you go that route) can only clean out carbon deposits. It won't revive worn out or overheated seal springs or restore the chrome surface of the housings, which are the usual causes of low compression in a race motor. Race motors usually don't have carbon deposit problems because of the manner in which they are driven. If you do need a rebuild, invest your money in as many new and carefulley refurbished parts as possible. Always new rotor housings, apex seals and all seal springs. Avoid the Viton oil control o-rings (they tend to last 10K miles on the street motors we've seen), but Viton is usually good for water seals (in the right grade), dowel o-rings, rear stationary gear o-rings, and oil pedistal o-rings. Also avoid all aftermarket apex seals other than ceramics. Seriously, they are all crap IMHO. Some are usefull for limited applications (like breaking in an engine before installing ceramics), but they all are inferior the Mazda factory seals. For a race engine, you might want to go with carbon-aluminum seals, but ceramics would give you a big boost in mid-range torque and last virtually forever (multiple refreshenings of the engine). Seasoned bearings are usually preferable to new ones. Other than that, just do a very carefull clearancing and assembly. The rules don't allow you to do many of the trick things, so you just have to invest in quality parts and attention to detail...or just go out and buy a used motor and have fun until that one wears out too. Rinse and repeat.

Mazda12AGS

I have a question, which vacuum line would you pull the water in though, any of them or does it need to be a certain one.

Kentetsu

The very first time that I cleaned out my engine, I used the water method via the brake booster vacuum line. Maybe it was just a coincidence, but my cat split and all the water ran out under the car and it was extremely loud after that. After I replaced my exhaust system I started using the Seafoam method as I stated above and have had great results. Just my 2 cents...

Blake

Any vacuum line far up enough in the system to "see" both rotors. On a carb'd car, it's probably best to just pour down the primary throats.

The brake booster vacuum line is not what you should have used...too big and not something that will get to both rotors. And how in the Hell did the water get through the engine while it was running without turning to steam? Something fishy there. The method has always worked for me and I've never heard of any other problems.

Kentetsu

I'm sure that the cat was already shot at that point. Maybe the steam was collecting in the cat and converting back to liquid, or maybe it just went in too fast due to the line that I used. I don't remember, this was a few years ago and I was just a stupid noob back then.

SCCAIT7

My issue is that with this being a race car... it cant be driven on the street... the only time its driven is when I go racing... The last time i took it out of the road... well... it took ALLOT of talking and explaining to the ossifer why I was out on the street with a car that was loud and 4 inches off the ground...no interior..guauges and a HUGE tach sitting in the center of my dash...5 point harness...did I mention the roll cage? lol... nayway... I paid a "wreckless driving ticket" for that one...125 bucks...

I mean... I can let the engine run in my driveway...but I really have no way to drive it...

Compression was taken with the engine warm... Throtle was closed... spun the engine over and watched it bounce...

trochoid

iTrader: (6)

Ah, throttle plates must be wide open. Can't compress air if there isn't any there to compress. Give it another try.

I would like to have seen the look on the officer's face when he saw you go by.

SCCAIT7

It was quite interesting... I am just happy they didn't take the car... I think that my only saving grace was that I was only a mile from home...

Kentetsu

Maybe you should have offered to take him for a ride. lol. Good luck man, try that compression test again...