bad oil pump??

[streetraceboi]

a friend of mine just bought a non-running 91 gst. when he bought the car they told him that the engine was no good because it was locked. so we checked the car at his house and it turns out the motor wasnt locked, in fact, it has clean/new oil in it. it had a missing timing belt tensioner so we put a new one, set the timing, and noticed that the oil pump sprocket was hard to turn. so we turned the car on and heard knocking. so we did a compression test and it read: 135,145,145,150. that seemed to me like ok compression. so now were stumped because we cant figure out where the knocking is coming from, could it be because no oil pressure from the oil pump?? if the engine was bad, wouldnt it read very low compression?? where is the knocking coming from??

 

[98TsiAWD]

Thread moved to Problem Diagnosis.

 

[BUCK]

-I take it the car still doesn't run.
-When you say turned it on I take it you mean you turned it over with the starter & it knocked...
-I take it you turned the oil pump with the timing belt off...
- & I take it your sure it's in proper time with a new timing belt.

It could easily have good compression, a good oil pump & bad rod bearings which is a common source of a knock - as well as guys have reported balance shafts "knocking" - pulling the oil pan would be the way to get to the rod bearings & see the balance shafts.

The Oil pump gear is bolted to the rear balance shaft - that shaft is heavy & the Oil pump could be stiff to turn if it set up for a while & the balance shaft bearings were dry.

I'd pull the valve cover too & look around for potential knocks.

Good Luck

 

[lowavenger96]

No compression has nothing to do with a spun bearing . That would be my guess >

 

[GTM]

Originally posted by streetraceboi

...
set the timing, and noticed that the oil pump sprocket was hard to turn. so we turned the car on and heard knocking. so we did a compression test and it read: 135,145,145,150. that seemed to me like ok compression. so now were stumped because we cant figure out where the knocking is coming from, could it be because no oil pressure from the oil pump?? if the engine was bad, wouldnt it read very low compression?? where is the knocking coming from??

Interesting situation here, compression is a bit on the low side with the 135 but well within specs especially if you gauge is reading low.

Two or 3 things concern me, first is the timing correct so there is no doubt it's dead on. This is not the time for guessing for it's so easy to bend valves.

Next, did you have oil pressure when you had it running(?) or was the knock heard while cranking??

That balance shaft/ oil pump drive must also be timed just as the other does. I don't like your reporting of it being hard to turn (must be checked with the belt off). I am suspicious you have a problem there. You should be able to use a battery drill and spin that up to prime the oil system including the hydraulic valve adjusters.

I'm not a DSM expert but thought I had read it;s possible for the crank to foul the balance shaft when it gets too far out of time. Anybody confirm this?????

You should look at the cam followers to make sure they are all seated for they might have fallen out and getting hit by the cam.

If the engine can safely be run you can sometimes isolate a rod knock by pulling 1 spark plug wire at a time to see if the knock dissapears or is reduced on just 1 cylinder.

Another thought though remote is spark plug wires hooked up wrong though less common on a 4 clyr engine. If one fires way too early on the compression stroke it will cause significant piston slap which could be mistaken for a rod knock.

Again with the engine running a good probe stethscope on different areas of the block can hear if it's a rod that is about to let go.

You of course know not to rev the engine until you know exactly what the problems is. You can pop the lifters out with the crank at 90 degrees, leave the spark plugs out you may be able to hear the knock during cranking.

Keep us posted, I'd like to know what you find or if we can answer more questions if you can provide more info.

Cheers,
GTM

 

[streetraceboi]

the knocking only comes when the car is on, not while cranking. we'll probably take the pan off today so we can see if it has bad bearings or rods. im pretty sure that the timing is on correct, but ill retime it to be on the safe side. also, we turned the car on with on balance shaft belt on, i dont think that would cause it to knock though, maybe it will cause it?? also, it has trouble starting. we did not get to look at the oil pressure gauge when we had it on, but it doesnt knock while cranking. and of course i turno the oil pump sprocket with the belt off, and it is hard to turn. ill try some of the stuff you mentioned and will keep you posted on how its going.

 

[bjones18]

the knocking only comes when the car is on, not while cranking. we'll probably take the pan off today so we can see if it has bad bearings or rods. im pretty sure that the timing is on correct, but ill retime it to be on the safe side. also, we turned the car on with on balance shaft belt on, i dont think that would cause it to knock though, maybe it will cause it?? also, it has trouble starting. we did not get to look at the oil pressure gauge when we had it on, but it doesnt knock while cranking. and of course i turno the oil pump sprocket with the belt off, and it is hard to turn. ill try some of the stuff you mentioned and will keep you posted on how its going.

Sounds like the rear balance shaft bearing has locked to the balance shaft and is rotating in the block.

The knocking may be a timing effect from skipping a cog on the timing belt due to the impact of breaking the balance shaft bearing free.

I just disassembled an engine with this problem, I didn't hear it running, but I saw the bent valves.