Compression

[Ty#0318]

After problem with starting the engine (slow cranking and fuel mixed with oil) I've checked compression.
On the 3rd it is.......0 On the rest 30-90psi
I'm dwelling about buying new (used) block or rebuil it.
What is Yours suggestion?
Is it the same part as a plain 4.3 V6 Vortec?
Will 2001 block fit instead of my dead one?
I have a possibility to buy it for good money. About 850USD for like below...

It has a very nice compression a 1yr of guarranty.

 

[SyTyAddict]

Re: Compression

Some here have said that the('96-up) vortec block and cranks are weaker than the older non-balance shaft blocks, something about GM put less material on them to save weight, they also have higher compression that the original SyTy motor. If it is just a stockish rebuilt, you could likely make it hold up decent if it has a great tune and possibly less boost.

I know there are a couple members here that have swapped the newer motors as a budget build, but it does require some modifications (Lower intake conversion, drill tap for knock sensor, etc.)

Personally I would find a lb4 block and upgrade the rods and pistons, and at least do main studs if not 4 bolt splayed mains.

Hopefully this helps some.

 

[qbnkiller]

Re: Compression

before you write off your engine, check to make sure your compression tester is working correctly. I had a faulty valve in the tester freak me out until I checked the tool out.

As for the VOREC block/engine, I would do it. It should be a higher compression then your existing engine (9.5:1 if I remember), but tune around that and you'll be fine.

 

[dgoodhue]

Re: Compression

I agree that you will need to tune for combo. I have heard the engine block has less material, but the oil pan on the newer motor provides additional structural support to the block. With stock internals the block isn't the weak point.

 

[Beavis]

Re: Compression

Check the head/s, could be a valve not sealing.....

 

[The Bronze]

Slow crank isn't low compression, that would speed it up. A cylinder without compression would give you engine speed UP whenever it was coming up to TDC on the offending cylinder. No tool needed. I agree with checking the tester. Make sure it has a good check valve at the end of the hose. Steal one out of you tire if necessary!

Look for a good battery, no voltage drops on the cables and no spark/fuel issues.

 

[Ty#0318]

Re: Compression

Thank You gentlemen.

I will check my tester first, then battery (new Optima) and starter. I've found additional (not serial) relay connected with the starter...
Maybe my 3rd piston is blocked in the cylinder. I will try to put something into a spark hole and check if this piston is moving properly.
It's like it has no power to rotate all these things.

Another question...
I wonder if low crancking speed could have impact on compression test results?

 

[Ty#0318]

Re: Compression

I add that my sparks are in terrible shape and my FPR is damaged...
I removed distributor and upper intake. Distributor was a disaster.
Today I will try to check valves.

 

[Quickstop [UK]]

Re: Compression

Thank You gentlemen.

I will check my tester first, then battery (new Optima) and starter. I've found additional (not serial) relay connected with the starter...
Maybe my 3rd piston is blocked in the cylinder. I will try to put something into a spark hole and check if this piston is moving properly.
It's like it has no power to rotate all these things.

Another question...
I wonder if low cranking speed could have impact on compression test results?

Have you adjusted the rockers on #3? If not, try taking the rocker arm completely off just to rule out a valve.

All cylinders have a bit of a leak so if it is really slow to crank then maybe it would show lower the compression. With plugs out on all 6 though, engine should spin pretty fast.

Bad starter motor?

Good luck.

 

[The Bronze]

Re: Compression

Just wanted to add that a slow crank can be improper ignition timing as well.

 

[Syclone22]

Re: Compression

I add that my sparks are in terrible shape and my FPR is damaged...
I removed distributor and upper intake. Distributor was a disaster.
Today I will try to check valves.

Don,t replace the engine just build it better with forged pistons !! :tup:

 

[Syclone22]

Re: Compression

Thank You gentlemen.

I will check my tester first, then battery (new Optima) and starter. I've found additional (not serial) relay connected with the starter...
Maybe my 3rd piston is blocked in the cylinder. I will try to put something into a spark hole and check if this piston is moving properly.
It's like it has no power to rotate all these things.

Another question...
I wonder if low crancking speed could have impact on compression test results?

Of course slow cranking speed will reduce compression
try again with a fully charged battery and hold the throttle body open
when checking compression !! :rant: