rx_rotary

I did a compression check on a 88T2(rebuilt according to owner).First car wont start so this is with the engine cold. I removed the lower plugs and am using a regular piston compression tester.I didnt remove valve.
k.Here's the thing. Battery was low and so first time I tested i got 30psi total pressure front and near the same for rear rotor. Well put in battery from my my 88 nova. This time I got 60psi total on front and rear rotor near same(around 63). well I held the valve near the gauge in and tested each face and I got 30-35 on each face. same for rear.so everything is equal so thats good.
question is...
Why do u think im only getting 60psi on total?
Is 30-35psi good on faces?
Also I've tried searching and i see most say put in leading plug holes but i've seen a couple say put in trailing holes and in the FSM it shows to put in trailing holes.

Go48

iTrader: (7)

Check the values in the factory shop manual (available from one of the links in the 2nd gen FAQ). In general, those numbers do not look good. The "total" number as you acquired it is pretty much meaningless. You could have a bad apex seal resulting in low or no compression in two faces and still get a good "total" number from the one good face. The compression on each face and the difference between the faces and between the rotors is the important information. In addition, the engine cranking RPM and the elevation of the location where the readings were taken must be used to "normalize" the readings for comparison to the specs in the FSM (again, check the manual).

However, that said, if the 30-35 PSI numbers are anywhere near accurate, your engine is badly in need of a rebuild. Best to have it checked by a rotary shop before you spend the money for a rebuild.

RETed

Did you remove BOTH front AND rear spark plugs?
Trailings are prefered; leadings will give a slightly lower reading.

Did you prop the throttle fully open?

If so, then proceed below.
If not, redo the compression check following the above criteria.

A cold engine will usually give HIGHER compression numbers.

Just newly rebuilt?
Then I wouldn't be surprised...

Just rebuilt with some miles on it?
If those numbers are accurate, something is wrong.


-Ted

jacobcartmill

iTrader: (6)

****, ted, even newly rebuilt, i'd expect to see atleast 90psi.

a monkey can assemble a 13b and get higher than 60psi...

RETed

Depends on who is doing the rebuild.

I tend to use a lot of motor oil on assembly...and you're right, I get 90's no problem.

I've seen engines newly rebuilt by others who have trouble cracking 60's.


-Ted

rx_rotary

k.im gonna remove the valve and try it again.
I think it should be fine but the battery I used has 545Cranking amps.
The engine supposedly has 5 miles on it.
I removed just the leading plugs on both the front and rear rotor.
Throttle was fully open

RETed- U still loacted on oahu?

SirCygnus

iTrader: (1)

sometimes it takes a bit of time to build up compression on a rebuilt engine using used housings or whatnot.

rx_rotary

well i tested it again with valve removed from tester.Got 30 on all 3 faces. on both rotors. The owner said a friend rebuilt the motor.and I can see motor has been touched because I can see all the fresh sealant. According to the owner he started it before when he first got it and ran it for like 5-10min.then he started it couple more times later. then after that it had a real hard time starting and now it starts just off an on and he's getting frustraded. So do u think the motor is actually junk or maybe my compression tester or??? just looking for some idea's.

The car is running megasquirt.
Also when I popped the plugs out to check the compression the plugs were very rich.So i believe their fouled out.

But really just trying to see if u guys think the motor really is bad or not and if im wasting my time trying to start it.

turboefini88

iTrader: (1)

First. Goto the FAQ section for the 2nd GEN. Find the test proceedurse for compression test and follow them. The numbers are there also.

You will get a million answers here and maybe 3 of them will be right. (not referring to you TED your one of the good guys )

Im just a stickler to following FSM/Mitchells on Demand for what I need to look at unless I personally have found or learned a new way to do it.

RotaryEvolution

iTrader: (30)

proper procedure to me is:

1) remove the schrader valve from the end of the hose where it goes to the engine, leave the top vent schrader in place or it will dump off pressure and drop your readings.
2) remove both leading plugs from front and rear housings
3) pop out the EGI fuse under the hood to disable the ign/fuel
4) install the gauge in the leading plug slot of your choice for first test
5) have an assistant hold the throttle wide open and crank the engine while you watch the gauge, do not touch the vent valve near the top of the tester.
6) watch the peak bounces, they should be even as well, to see if the bounces are even watch the fat portion of the needle near its base with your eye and you will see inconsistencies at that point.
7) repeat procedure for the other rotor housing and compare the readings.
8) reassemble your work in the reverse order.


this is typically done on a warm engine for accurate results but sometimes with non running engines for diagnostic purposes you can only do this when cold. the readings should be at least 85PSI per rotor. anything below 70PSI the engine will be difficult to start.

make sure the battery is fully charged, jumping the battery with a booster or another car will help keep your results more accurate as cranking speeds increase so will your compression so trying to keep your cranking speed consistent is also important.

rx_rotary

well this time I used a good battery out of my van and I did the testing according to procedure.

What im wondering is.if the owner really started the car. How could the compression be 30psi.
I mean what im askn is,is it even possible to start and run a car that only has
30psi of compression?
When I blew one of my apex seals on my T2 i used to have it sounded like total crap.and ran just as bad.

RotaryEvolution

iTrader: (30)

if the compression is an even 30PSI it may start with the help of some oil in the chambers but i doubt he would be able to get it starting without assistance such as that.

he could have effed up and left the short apex seal ends out(boots) for all we know..

doesn't surprise me if the builder was inexperienced or didn't pay attention to the details.

rx_rotary

alright.and here's another thing i rememberd
he doesnt have the omp hooked up.I think he said he ran premix but
I'm not positive.
But that could of been a possiblity right? or would it take longer?
If he ran no premix without the omp hooked up and ran the car for maybe 20
minutes overall time.would that be enough to ruin it.

RotaryEvolution

iTrader: (30)

it takes several thousand miles for an engine with no premix/OMP to start showing signs of engine damage so i would say no. the engine assembly lube usually aids the engine during the first 15 minutes of engine run time anyways so i doubt that can be any issue.

rx_rotary

ok.well thanks for all the help Karack!! I'll be sure to post if I get the car started

TehMonkay

iTrader: (-1)

Did you try pull starting the car?

rx_rotary

no.havent tried that yet.tried flooding the engine on purpose today and pulled the plugs and didnt smell fuel.so I gotta make sure I got fuel coming.and then ill try puting some oil and starting it.then after that ill try push starting it.