Can the LL8 be cranked for testing outside of vehicle?

[KWG2005]

In the past I have cranked junkyard engines with the starter motor to see if they have compression. You can also determine if there is oil pressure. (obviously not a reliable determination of how much pressure since crank is slow). But you can see that it is building something. These were older engines before VVT. I have my LL8 almost ready to install into the trailblazer after a complete rebuild. Is there any reason this engine can't be cranked outside of the vehicle for testing purposes?

Thanks for your help.

 

[Mooseman]

I can't see why not. If you fill it with oil and hook a battery directly to the starter, it will crank. VVT system will just stay at it's default advanced position without oil pressure or control from the PCM.

 

[azswiss]

. . . and prime the oil pump.

 

[KWG2005]

Well I cranked it. It delivered enough oil pressure to trigger the switch, which is good I suppose, especially for just cranking. The compression does concern me though.

Cyl 1: 180 psi
Cyl 2: 150
Cyl 3: 140
Cyl 4: 140
Cyl 5: 180
Cyl 6: 180

I'm not sure what the compression is supposed to be. The results were even lower because I was cranking off a battery I soon determined was weak. Then I jumped it off my running Grand Cherokee and got the better results. It's wonder if it could be because it's not broken in, or because there could be more oil on the walls of some of the cylinder than others. I put oil on the cylinder walls a long time ago to keep them from rusting while working on the engine.

 

[azswiss]

You would expect to see well under 20% difference between the highest & lowest cylinders on a fresh rebuild. Were the cylinders bored and/or honed? New rings? Ring gaps not overlapping? Head rebuilt (valves/seats ground/replaced)? Assuming yes to these questions I would squirt some oil into each cylinder and then retest.

 

[KWG2005]

You would expect to see well under 20% difference between the highest & lowest cylinders on a fresh rebuild. Were the cylinders bored and/or honed? New rings? Ring gaps not overlapping? Head rebuilt (valves/seats ground/replaced)? Assuming yes to these questions I would squirt some oil into each cylinder and then retest.

I honed the cylinders. They weren't that bad to begin with. The cylinder head was remanufactured by Clearwater Cylinder Heads. I think my pressure gauge might be the problem. I am getting inconsistent results with it. I think perhaps it isn't seating properly in the plug hole. I'll look into it more later.

I think the starter is turning around 120ish rpm. I wonder if that's fast enough for the crank to fling oil on the cylinder walls.

Thanks for the advice.

 

[flyboy2610]

Looking at the numbers, #2 is a bit low, but still within 20% of 180.
#'s 3 and 4 are definitely low. If you continue to see low numbers between those two cylinders, a head gasket issue would be my first guess. Check the block for flatness or cracks as well.

 

[KWG2005]

Looking at the numbers, #2 is a bit low, but still within 20% of 180.
#'s 3 and 4 are definitely low. If you continue to see low numbers between those two cylinders, a head gasket issue would be my first guess. Check the block for flatness or cracks as well.

I tested again and got: in order 1-6

185
150
150
185
190
190

Cylinder 4 went from 140 to 185. I think my tool is wonky. It's a Craftsman test kit I got about 10-15 years ago. I do recall weird test results before and shrugged it off. The engine I got from a junkyard for my Alero, the compression was out more than my liking but that engine ran fine for years. I wonder if it is indeed the tool.

 

[Mooseman]

Those numbers are a bit low compared to those I got a few years back when I was chasing a miss at idle. Could be because of the fresh rings and hone. Maybe do a leakdown test to see where it's going. If going through the valves or head gasket, at least you can get at it now. If it's going into the crankcase, I'd blame the rings/hone and let them wear in.

For the head gasket, @mrrsm found an issue with one brand where there is a rivet that holds the MLS gaskets together in a wrong place and getting sandwiched between the head and block surfaces, causing a leak.

 

[KWG2005]

Those numbers are a bit low compared to those I got a few years back when I was chasing a miss at idle. Could be because of the fresh rings and hone. Maybe do a leakdown test to see where it's going. If going through the valves or head gasket, at least you can get at it now. If it's going into the crankcase, I'd blame the rings/hone and let them wear in.

For the head gasket, @mrrsm found an issue with one brand where there is a rivet that holds the MLS gaskets together in a wrong place and getting sandwiched between the head and block surfaces, causing a leak.

Thanks Mooseman. I'll do a leak down test. I was aware of the rivet issue with the head gasket, and I was sure my rivets were all in places where there was a cutout in the head/block.

 

[KWG2005]

Bad news. The engine leaks out of every exhaust port and one of the intake ports. Here's my leakdown results. This is with 100 psi pumped in at TDC of compression stroke.

1: 80psi, mostly crankcase, but leaks out exhaust valves
2: 80psi, mostly crankcase, but leaks out exhaust valves
3: 30psi, mostly leaks out intake valves
4: 85psi, mostly crankcase, but leaks out exhaust valves
5: 95 psi, slight exhaust leakage
6: 80psi. mostly crankcase, but leaks out exhaust valves

It looks like #5 is the only cylinder that passes the 90% test. I am thinking maybe I should cover up the exhaust ports and see what it would be without a leaking exhaust port. If it went from 80 to 85% would that be good enough? I'm asking because if I had a perfect head on and I only got 85%, would that pass? Clearly most of the loss is valves, especially on #3 which is totally unacceptable.

I should not have trusted an online cylinder head manufacturer. The challenges to this project are not the difficulty of this engine, it's the poor quality parts I have gotten. I suppose I could have gotten a head done locally and had the same problem... but I doubt it. I got the head from Clearwater Cylinder Heads. I don't know if anyone else had experience with them.

$114 of head bolts down the drain. According to Felpro you can re-use the head gasket as long as the engine was not brought up to temp. It took me 2 weeks to get that head gasket. They kept arriving damaged, and then fedex lost the last one. I'll need to re-order TTY bolts for the cam sprockets as well.

I would have thought the cylinder had would have been tested for sealing before it went out the door, but today it seems there is no quality.

 

[KWG2005]

A follow up for everyone. 2 weeks ago I got my cylinder head back from Head Works of Nashville. They did a fantastic job. They confirmed most of the valves were leaking on the head remanufactured by Clearwater Cylinder Head. They put all new intake valves in. I put it on the engine and got 90% or more on all cylinders on a leak down test. The Compression was around 210 psi on all cylinders. I installed the engine last weekend. The vehicle is running very well. Quiet and smooth. I can put a wine glass on the engine and it would barely move. The only thing I need to tackle is a slight stumble when i gently press the gas when vehicle is in park or neutral. It will catch itself but rpm will fall for a second. Maybe a fuel pressure regulator or something? No codes. No hesitations or anything while in gear, or if I give it more gas when in neutral or park. Only happens when giving it a tiny amount of gas while out of gear. I read somewhere that these cars need a throttle re-learn. I didn't do that so perhaps that's the issue. I'll do that first before looking elsewhere. Thanks for everyone's input on the forum.

 

[Mooseman]

The only throttle relearn is when the TB is cleaned, the battery or the fuses need to be pulled for 30 minutes to reset it. Usually causes a poor idle, especially with A/C on.

I had a stumble like your on my 02, never was able too figure it out.

 

[KWG2005]

The only throttle relearn is when the TB is cleaned, the battery or the fuses need to be pulled for 30 minutes to reset it. Usually causes a poor idle, especially with A/C on.

I had a stumble like your on my 02, never was able too figure it out.

Thanks for the input. It isn't a huge deal, just a bit strange. If it's idling at 700 rpm in park, I touch the throttle a tad to rev it slightly, it will fall to about 400 or so and almost die but catch it. Sometimes the oil pressure warning comes up for a second since the rpm fell so low the oil pressure must have fallen below the threshold. Anyway, I'll think about it but it's not a big deal.

 

[TollKeeper]

I would think a Crankshaft correlation relearn would be needed with the rebuilt engine?

 

[Mooseman]

Wouldn't hurt to do the CASE relearn. I did multiple and didn't do anything for me unless I had a code specifically for it.

 

[KWG2005]

I need to get a different scan tool that can do the crank/cam relearn. I have a simple scan tool. I started going down the rabbit hole of scan tools. I'd like one that can do the relearns but it also bi-directional and can record many data points at the same time. Oh, and it would be nice if it weren't expensive.

 

[TollKeeper]

I think @mrrsm may have some input for you on that one. I have a Tech2, and works for my wives Saturn, and my GMT, and my prior vehicles. I like the functionality of the Autel Maxasys, but they are rather pricey!

 

[Mooseman]

I just bought this one and it seems to fill all of my needs except that to do a CASE relearn, you have to buy that feature ($30cad). Still cheaper than going to a shop. I got it on sale.

LAUNCH OBD2 Scanner,2023 Newest CRP129X Elite Scan Tool, 8 Reset TPMS/Oil/EPB/SAS/BMS/Throttle Reset,Injector Coding, Lifetime Free Wi-Fi Update, ABS/SRS/TCM/Engine Car Scanner,Auto VIN, Battery Test https://www.amazon.ca/dp/B07RK9GCK3/?tag=gmtnation-20

 

[KWG2005]

Very nice Mooseman. The whole scan tool is probably cheaper than the dealer nowadays. ToolKeeper, when you say Tech2, do you mean the official GM tool?

 

[TollKeeper]

I do..