jjausnoint

Hey, first of all let me start my saying this is going to be my first rotary engine vehicle. I have had experience with regular engines, but i wanted to start something new and get into the rotary thing.

I found a vehicle that is very clean for a good price, catch is it says it has a "spun bearing"

I am familiar with how rotary engines work, and i was searching the web, and i could not find a place to order engine bearings for the 87 Rx7.

Should i move on and try to find a different one? I am really not looking to swap but if i could just get the bearing that would be awesome.

Any help is appreciated, Thanks.

pfsantos

iTrader: (1)

Hmmm, spun bearing...find out which one. If it's one that's easy to get to (like a thrust bearing behind the front cover, although this can cause other problems), maybe it's worth it, if it's a rotor or eccentric shaft bearing, then it better be a da*n good deal.

RoTa7

spun bearing in the tranny?

jjausnoint

engine

http://seattle.craigslist.org/see/car/343423552.html

That's the car i am referring to.

NOPR

you will need an entire engine rebuild, possibly a new engine. There are bearings in the rotor that turns on the eccentric shaft lobes and in the stationary gear that the e-shaft rides on. My only experience is a spun rotor bearing. if they are spun, most likely the rotor is fucked. new bearings can be ordered through mazda or mazdatrix, but thats the least of your worries. With a spun bearing LOTS of other **** can go bad. the bearing may be friction welded onto the e-shaft and totally seized. the rotor may have jumped around when it seized and done all sorts of bad things to the housings and irons. there are probably plenty of metal shavings in the oil, so a lot of components (oil cooler) will need replaced. a spun bearing is what i would consider a catastrophic engine failure, and you may want to look for a different RX-7 to be your first.

jjausnoint

Thank you, i shall continue looking.

Aaron Cake

iTrader: (1)

If a bearing has spun, all parts of the rotating assembly are likely trash. You'll need to replace both rotor bearings, the stationary gears, stationary gear bearings and the eccentric shaft. You may also have to replace the following the oil pump and front stack components (thrust washers and bearings), rotors and irons if the damage is severe enough.

All these parts can be ordred from your local Mazda dealer, including the bearings. Parts catalog is in the FAQ.

Here's a few pictures of what happens when an engine spins a bearing:
http://www.aaroncake.net/rx-7/damage.htm

jjausnoint

Oh, thank you very much for the link, much appreciated, i look forward to getting an Rx-7

SpeedOfLife

iTrader: (16)

What are some fundamental maintenance practices to prevent spun bearings in the motor? Keeping your oil system working right or is there more to it?

arghx

iTrader: (3)

I don't doubt that it needs the motor rebuilt, but I'd get a second opinion on the spun bearing. This is not a common problem on a rotary... the only one I've ever seen happened on a motor that had the timing WAY off.

As far as maintainance and low oil... well about 6 months ago I changed the oil on my Turbo II, and my boost controller line got pinched between the filter and the block. So unbeknownst to me, oil spewed everywhere as I drove it around the block and to the gas station (low oil light wasn't working apparently). I let it idle at the gas station for a good 10 minutes as I filled the air in the tires, until I realized there was a small pool of oil on the ground.

Guess how much oil had leaked out? 4 quarts. I changed the oil again and had no metal shavings. It ran like a champ after that. I killed a 350z a couple days later...

Ottoman

i'm honestly suprised..

never even heard of anyone with a spun bearing on our motors


sounds to me like the previous owner has no clue what he's talking about...

SpeedOfLife

iTrader: (16)

I've heard of a spun rotor bearing, and even if I hadn't, if there's a bearing, there's the possibility it will spin on or in whatever it's in or on.

Aaron Cake

iTrader: (1)

Bearings will only spin if there is a lubrication problem (lost oil pressure) or they were installed incorrectly. It's very rare for a perfectly running engine to spin a bearing.

RotaryResurrection

iTrader: (8)

There is such thing as a spun bearing in a rotary..about 1 out of 15 engines I get have them.

On original engines, bearings only spin if you run low/dry of oil.

On rebuilds bearings tend to spin much more, I attribute this to the fact that the bearings were replaced during the rebuild. Each time you press out an old bearing and press in a new one, you actually take out a small amount of material from the rotor/gear it was in. This makes the new one more likely to spin, as the only thing holding the bearing in position is the friction between it and the rotor/gear it sits in. Rebuilders who replace bearings as a matter of course for every rebuild are not doing themselves or their customers a favor...I only replace bearings when I have to, and the originals are preferrable to the new ones in terms of clearance, strength (heat cycling over their life) and unlikeliness to spin.

When a rotor or main bearing spins it destroys the e-shaft and the rotor/gear it is in. IT also lets the shaft or rotor move around a lot more than normal, and so the rotor winds up contacting other parts that it should not...you will get irons scorched and cracked from the rotor rubbing the sides, and you will get rotorhousings that may have issues because the rotor was slapping them.

The bearing material also goes through the oil system and chews up everything it touches...the oilpumps are sometimes bad, and sometimes fine. The other bearings in the engine are usually junk.

Best case scenario for a spun bearing engine is that you need one rotor/gear, and the eshaft, and new coolant seals/orings.

Worst case scenario is that you need all 3 irons, all 4 bearings, a rotor and an e-shaft, and all new seals.

SpeedOfLife

iTrader: (16)

^^^ great info, totally answered my question and then some!