Starter Motor effects Compression?
 

I'm only asking this question because the mechanic at Mazda told me this and I doesn't make any sense to me. The car went in for a compression test, compression was low. The did a voltage test and everything was good.BUT they said before we go ahead with the warranty you have to buy a new starter because that could be effecting the compression problem.

Ok I'm not a mechanic by no means but how dose a starter (external engine component) effect the compression of an engine?


Thanks!

No, the starter does not affect the compression of the engine.

However, the speed at which the engine spins affects compression. Compression tests are done by spinning the engine with the starter. So if the starter can't spin the engine fast enough (within spec for the test), then the starter could be blamed as a cause for the low compression test results. Doesn't mean that the engine compression is low, just that the test was low, possibly because of the starter's crank speed.

However, they do have a correction chart available.
http://www.twistedrotors.com/images/..._Comp_Test.jpg

If you know what speed the starter was cranking it at, then you can see where the pass/fail line is.

If the crank speed is under ~220rpm or so, it's recommended to replace it, regardless of what the engine compression is, to save you from hard starts, flooding, etc...

No, it doesn't effect compression. A faster starter will give you a higher crank speed which will result in HIGHER compression ratings. But if they use the updated compression test by Mazda it should convert it to 250 which is what mazda's spec is. Anything under 6.9 @250 is failing.

Thanks thats put in better context lol

Here is what mazda sent me maybe you guys can help

Thanks!

Rotor 1 *520*530*560* RPM 187
Rotor 2 *560*500*520* RPM 184


Vaccum/ Voltage

KOEO,BARO voltage 3.962v
KOEO,BARO voltage 2.107(after 5 minutes)

MODE6

Catswitch ratio 0.253

Misfire counts

Rotor1 28 (last 10 drive cycles) 4
Rotor2 23(last 10 drive cycles) 4

Those numbers look pretty low but your starter does look a bit low as well.
They should have a converter to tell you the compression @250.

I just purchased a brand new N3Z118400 OEM Starter for $454 but you can get a reman for around $330 without core charge. (give them old starter)

I'm just really fussy so I went with a brand new one.

EDIT: Just saw you updated your location to Canada.

SpeedofREV 187RPM ------------------------------- SPEED OF REV 185RPM

--------------Measure ----- Compen(250rpm) ------------ test 2
Chamber 1 : 524 ----- 637.69 ------- 540 ----- 695.23
Chamber 2 : 534 ------- 683.69 ------- 538 ----- 693.23
Chamber 3 : 569 ------ 718.69 ------ 512 ---- 667.23
Diff chambers : 45 ------ 45.00 ------ 28 ------ 28.00
Diff rotors : 524 -------- 524 ----- 512 ------ 512.00

If those are the converted numbers those are defiantly failing.
Tell them you'll purchase a new starter after they call Mazda to issue you a replacement engine or you'll try else where. They get paid to do the replacement, it's not like they work for free but if your car is close to being out of warranty they make a lot more profit which is why they would try to fight it. A re-manufactured engine from Mazda alone is $2,700.

That starter speed is REALLY low. I'm surprised you can start the car at all? I think your corrected compression is probably within spec once you have a normal 250rpm starter speed. At 200rpm my 8 had a terrifically hard time starting, with high 7s, low 8s. If you can start at 187rpm, your compression is probably well above average. If you can't start it, it could be average compression and the obviously failing starter.

What was the reason you brought it in? "Just because" compression test? Or specific complaint?

The conversion chart is posted above, and doesn't go under 200rpm, probably because that's the lowest speed that the engine is supposed to be able to start at :)

The second numbers i posted are off the actual print off with the graphs. Ill scan and post what they gave me.

The reason I brought it in is because the car was having trouble starting.(Girlfriends Car) First they told me Rx8's are all like that I argued with them and it didn't get me anywhere so i left and it got worse. I went back and they said you need new plugs that will fix it so new plugs. it was fine for about a week then bad again. The dealer does all the oil changes and "So called servicing" I checked the intake filter and tube it was completely filled with oil and the filter was black. Looked like it hasn't been replaced in years. I replaced filter and cleaned oil out and again it was fine for another week or so. Then I was told by a friend that Mazda has a Warranty on these engines so i brought it down for a compression test and voltage test. $200 later they send me these numbers and say I have to buy a new starter before they will look at warranty. Just figured id post here to get some info before I really looked in to it.

Thanks@!

The starter has been your problems all along. Replacing the ignition helped because it strengthened the spark, compensating for some of the lost ground from the starter. I'm going to bet that the engine is just fine.