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I'll be replacing Stinky's heart soon - filling in foe "Al", who was a no-show. Al is short for Albino, but Frank isn't short for anything. Stinky and I will be joined to form the "Frank-N-Stinky" road rip team.
No name change for Stinky - he's just got a tack-on like in a marriage.
The number I focus on is the first stroke of the compression test. I'm not disregarding the ultimate compression - it's good to know that your combustion isn't going to bleed out before it pushes the cylinder down. I'm operating on the theory a higher first hit of air at a fixed RPM means more power - turbo boost has the same effect. After all... when you're driving down the road, the truck isn't making several strokes to build compression before it fires - it's compress once and fire.
I can now see why there is no such thing as a set compression number when testing - the speed of the starter, the charge on the battery, and the gauge design have a huge impact as variables. One test yielded 230 average on the first stroke with an ultimate of 370 PSI max. I then used my gauge set (since I already have something to compare to) and gave the single battery a jump - and then I had 300 PSI first crank with 420-440 ultimate. When the engine is running down the road, the compression will be far higher.
I've rebuilt a few (gas) race engines in my day. I'm by no means a pro. What I know is that the compression reading on the first stroke is less helpful if the engine has been sitting, is cold, and the cylinders are "dry." Usually the reading is done after the fifth stroke or so, same for each cylinder, on a warm engine with the throttle wide open (not applicable here). I agree the consistency between cylinders is more important than the actual value.
A leakdown is more helpful, but more involved. It requires a special gauge (inexpensive and reasonably reliable from Harbor Freight), a small air compressor, and needs the valve covers off and a way to lock the crank in place. Then again, if you've gone this far (you have a borescope and thermal camera, right?), and this is your second engine donor, then you really ought to take this additional step.
Man, for your sake, I hope this second engine came from a pampered donor that suffered an electrical fire far from the engine bay. Not something that experienced more than 3 Gs as it was rolled/crushed to its demise.
The engine was on a shuttle van - and I don't know what happened to the van other than it was scrapped out. The van engines have some weird parts on them, so I know that part off the story is accurate.
I have been dealing with the vendor of this engine for years now. He's a bit expensive, but he's the one that keeps permanently fixing the difficult stuff, when the dealership and another local diesel mechanic just pat me on the head and tell me everything's fine. He's a member of the BBB, and he's never steered me wrong before.
I need to research this bleed-down test more - I tried it on Stinky and it was a total fail. Now that I actually have a Harbor Freight in town (opened this spring), I can get things quickly.
Having the engine undressed and on the stand in front of you at eye level is a great opportunity to really learn the beast. And I agree, Youtube is a decent source to familiarize yourself with new tools and skills like leakdown testing. In fact, it's where I learned basic machining for my bench-top mini lathe and mill. I put them to good use in building up my vintage race car.
You also mentioned having new access to a Harbor Freight. A lot of people will try to steer you away from it. I want to make the case that for your purposes, it's a reasonable resource to get this job done. It's true that HF does push a fair bit of garbage, and it seems that everyone you know has some horror story about them. But they also put some really decent tools into the amateur's hands for a fraction of what the real deal would cost. Thereby making real work (drilling/cutting/welding/shaping/lifting/painting/fastening) accessible to the infrequent user. Myself, I've had really good luck with their hydraulic, pneumatic, and basic hand tools. What do I know?
I mentioned my vintage race car earlier. I have its build documented in this megathread, if you have several hours to burn. Transformed it from a rusted, discarded shell to a reliable and competitive race car. I'm not ashamed to say that I'm 100% self-taught, and used a lot of Harbor Freight tools to build it. Over the years, I've gradually replaced the HF tools I used most with the usual Snap-On, Craftsman, Knipex, etc. Not because they work any better, but for my own pride. But I still like HF for hydraulic and pneumatic tools. Just don't skimp on the drill bits, saw blades, and abrasives.
Well, good luck on this engine. Don't be intimidated by the thought of tearing into things to make the task more accessible. A really good surgeon once told me that exposure is everything. It's all just nuts and bolts, anyway.
I cringe every time I go to HF - they are more cheese vendor than tool supplier. Saying that, I'm going to use an engine stand for this one job - then I have to get rid of it. Hoist is the same story. Big torque wrenches? Same. I need an economical way to work on big iron this one time, then have a going out of business sale.
As for the compression readings, they're balanced within spec. #5 is the most marginal on the first stroke at 260 compared to 300 on all the others, but the Ultimate came up to 400 in the same number of strokes. This leak test is the answer I'm looking for to double-verify before it's too late to take it back to the vendor. If I'm forced to do a rebuild, there are other options besides paying a premium for a running engine.
The only question I have is should I do the test, then shoot a little PB in there and repeat the test to record the difference?
I'm self-taught on almost everything I do - including my job. The technology is far too new to be get a chance to be taught how it works. The engineers and I are pretty much writing the books for the class as we go. So... I'm not easily intimidated. However... time availability has me abbreviating some processes with Stinky, and he's quick to burn me down when I do.
05-08-2016, 11:34 AM
I'm "Frank".
