How to understand compression issue. Rings or Valves? Video attracted

[BeemerNut]

Thank you all for the input. Found a shop that could do a proper compression test to determine if its the valves or rings. Still was quoted about $3500 for redoing a single head and about 4k for both heads. They quoted from the book that its 20 hours to pull a head. I dont like "the book" .
That leads be back to about $6k for heads and timing chain or $9k for engine at another place.
This may sound blasphemous, but I'm really wishing I had a Toyota Landcruiser right now! Timing belts are $900 to change!

This morning for the hell of it opened your compression check video.
*** was that?
Firtst time in over 55 years ever seeing a compression check done on a running engine vs by starter cranking speed.
I bet off the starter you had 75 psi at best.

On another note a cheap cylinder leak down tester;https://www.harborfreight.com/cylinder-leak-down-tester by Maddox-64918.html at $80. Best part is has twin 0-100 psi gauges.
On a El Cheapo live the Pittsburgh brand at $25 which is a POS in my book and the same item given to me by a friend given away NIB.
They zero out at 16 psi inlet pressure much too low to do a proper bleed down check plus their regulator leaks, pressure keeps creeping up then 0-100% scale is off.

Our FAA regulation standard is 80 psi inlet gauge pressure with 0-100 gauges, direct reading percentage off second gauge.

At 80 psi the most accurate plus allowing hearing hissing in oil filler, intake and exhaust valves.
The "El Cheaop" had" a 0.040" restriction orfice which I replaced with a 0.029" orfice plus twin 100 psi gauges. Now able to get accurate leak downs on 2" to 2.75" bore motorcycle engines.

With he 0.040" orfice it would make a small bore engine read only 3-5% leakdown when in real life the worn out engine having a 14% leak down. Circumference ring area difference of app 2.25 times. Then it's just a rough (ruff) reference tool and not an accurate one.


As with fellow aircraft mechanics, "if you can't work on it don't own it" regarding mechanics owning their own airplanes.

Do it yourself and save thousands unless money is no object.
All the best on your repair adventure.....~~=o&o>......

 

[Stuart Barnes]

Malubulr4, this is a good reference for compression testing and doing a cylinder drop down test/leak test.

https://www.mobil.com/en/lubricants...vehicle-maintenance/how-to-do-a-leakdown-test

also do you have the exact codes that the car is throwing?

And if you’re able to clear the code/cel and drive it for 30 minutes without anything being thrown then I’d be a bit skeptical of jumping straight in and changing heads etc.

Have you ruled out the simple stuff like poor fuel etc?

 

[BeemerNut]

Keep driving it with a misfiring issue that unburnt gas will burn in the converter overheating it torching, melting and twisting up the substrate material.
Now you'll have possible blockage issues plus a failed converter be it one or two cats off that cylinder bank. Add replacement cost to your already repair bill. I bet between the $350 and $500 plus range.......~~=o&o>......

 

[Red Top Engine]

The headgasket can be replaced without taking out engine and the heads & valves can be checked at a good machine shop. I suspect the valves. Replacing the cylinder rings is feasible but a real pain.

 

[gsxr]

So I might call around and see if I can hire a mechanic to do a proper leak down test to determine the issue.

Leakdown is critical. I agree 100% with @djkaosone. These direct-injection engines have no way to keep the valves clean. It's entirely plausible that your problem is simply "dirty valves" preventing them from closing fully. The leakdown would help narrow this down, and with the intake manifold off it could likely be pinpointed conclusively.

Here’s a question for everybody. Let’s say it’s determined that it is one of the valves. Could a perfectly working low mileage head from a junkyard or crashed car be placed on my block?

If it is the valves, first it's very possible that cleaning can fix the problem, without pulling the cylinder head off. But yes, there is no reason why a good used head couldn't be used, if it checks out OK (mounting surfaces flat within spec, etc).

Can just one head be done?

Of course. However, the additional cost to do the second head is incremental if one is being removed, so there's some logic to doing both while it's apart. This largely depends on how greedy the shop is doing the work.

Still was quoted about $3500 for redoing a single head and about 4k for both heads. They quoted from the book that its 20 hours to pull a head. I dont like "the book" . That leads be back to about $6k for heads and timing chain ...

I don't follow the numbers here. Are you saying $4k for rebuilding both heads, PLUS another $2k labor, for a total of $6k? That sounds nuts. Unless they are scrapping your heads (which is stupid) and installing different ones. You do not need to replace the head(s) unless they are cracked or otherwise beyond repair. Installing a used engine for $9k isn't going to be any better than fixing yours.

...or $9k for engine at another place.

The used engine is a gamble as you have no idea what the condition is without partially diassembling to inspect the valves, etc... plus it should at least receive an external re-seal. You don't need a replacement engine unless yours is destroyed. What I heard in the video in your original post is a motor that runs fine but has very low compression on at least one cylinder.