Leak down test to determine engine life?

[Kurtatron]

Hey Everyone.

I am in the midst of replacing a 1991 Toyota Previa engine with a used replacement. It's a JDM import. Thing is, I have my doubts this thing is actually a JDM. It is missing the Japanese market substitutes for the American market. It instead has the American parts. But what's done is done. It's not really an option to return this thing across the country. That story is for another time.

So not being sure of the Engine's origin, I am wondering if I can find out what kind of engine I have. Is it worn out like my old 200k engine, or is it like a low miles 60k JDM engine like I believed I was getting originally? The engine insides look great. No oil varnish at all. It had some surface rust, my guess from sitting around for decades. Is there a way to determine engine wear and life remaining? I was thinking a Leak Down test can give me leak percentages. Could that tell me what kind of condition the engine is in? Would there even be a difference between a 200k and 60k engine?

 

[andyd]

How far do you want to go? It sounds like you have the valve cover off. I never did a leak down test.Probably a good idea if you have the air and the fitting. I have removed the oil pan and pulled a bearing cap or 2 though. Looking at a crank journal will tell me the condition of the lower end. Leak down won't show that. Depending on how long the engine has sat, you may wanna change a few seals and gaskets.

 

[BrocLuno]

Leakdown is a good way to get a sense of the cylind3er condition. But, if it has some rust, there may be a rusty haze on one cylinder because it sat with one valve open and no full exhaust or intake to "protect" it...

So, if it was me, I'd pull the plugs and see if I could rent or borrow a bore scope and look at the combustion chambers and upper cylinder walls. If they look good, then I'd do a leak-down.

Reason I say this, Is I have had two engines show poor on leak-down and actually, the rings were stuck a bit. As soon as I put some WD40 in each of the cylinders and spun the motor, they came right back and tested fine (within 10% of the others).

On most used motors I'm like andyd, I want fresh bearings in the bottom end unless they look really nice, and plasti-gage well... I also want new front and rear seals on the crank and a pan gasket.

The other biggee for me is the condition of the timing chain or gears. If they look dry and beat up, but the rest of the engine looks good, I'd look at the oiling diagram and see if there is a way to get a wee bit more oil to them (like drill 0.030" hole in a gallery plug just above one of the gears or sprockets) so they will stay wet. Replace and cruise on.

The deal is that as engines wear, less and less oil gets to the front because of bearing leakage and the like. Plus, that Previa motor lays over IIRC ... So I don't know if they got all the oiling issues figured ...

Previa is interesting machine. But getting a bit scarce now

 

[Lolvoguy]

Originally Posted By: Kurtatron
Hey Everyone.

I am in the midst of replacing a 1991 Toyota Previa engine with a used replacement. It's a JDM import. Thing is, I have my doubts this thing is actually a JDM. It is missing the Japanese market substitutes for the American market. It instead has the American parts. But what's done is done. It's not really an option to return this thing across the country. That story is for another time.


I've always been one for a good story.

Please, do tell

 

[Silk]

Having fitted JDM engines for 30 years, they are usually in very good condition, at least compared to local engines. In the early days they often started up with a cyl or 2 out, but then settled down to run well. Just valves stuck open sitting for so long. Suppliers have sorted the issue, and they start up fine now.

 

[Olas]

There's no way to tell its heritage unless you know of all the differences between the two and can ID market-specific parts.

Best way to determine life is to strip and inspect.

 

[CorvairGeek]

I always 'loved' this about the Previa;





The "SAD", Secondary Accessory Drive.

 

[Kurtatron]

Originally Posted By: Silk
Having fitted JDM engines for 30 years, they are usually in very good condition, at least compared to local engines. In the early days they often started up with a cyl or 2 out, but then settled down to run well. Just valves stuck open sitting for so long. Suppliers have sorted the issue, and they start up fine now.


I hope you're right. All the internals of this engine look like the thing was given immaculate maintenance. No oil varnish to speak of, coolant passages clean, and a Japanese quality Nippon oil filter. I did measure the solid lifter gaps, and they were in spec. Since this is my first time doing an engine replacement, there are lot of things that are making me nervous. There is some surface rust on the cams, and beneath the oil pan, but it took nothing more than WD-40 and a scotch-brite to clean those up. I think this rust just came from sitting around for years. I really hope I can trust what you're saying here. Here are some well-deserved pictures. I'll post more about this after work.

 

[Kurtatron]

Originally Posted By: Olas
There's no way to tell its heritage unless you know of all the differences between the two and can ID market-specific parts.

Best way to determine life is to strip and inspect.


That's why I was wondering. If a JDM engine typically recieves good care, then if mine is not JDM then perhaps mine has not recieved that care. I dunno. I am worry wort at heart.

 

[BrocLuno]

That all looks good. I'd button it up and install

 

[Olas]

Originally Posted By: BrocLuno
That all looks good. I'd button it up and install

Along with new ignition parts just to be safe, what he said ^

 

[CBR.worm]

Be really careful with scotchbrite in and around engines. The abrasive material can be left behind and get washed into the oil causing excessive wear. GM used to have a bulletin about it.

 

[Kurtatron]

Originally Posted By: CBR.worm
Be really careful with scotchbrite in and around engines. The abrasive material can be left behind and get washed into the oil causing excessive wear. GM used to have a bulletin about it.


Yeah right, sorry. I meant to say blue shop towels, as seen below. I don't think they are abrasive, at least I hope not. I didn't think the rust was a big enough deal to try using abrasive pads.



And yeah, the engine is going in. I trust your opinions now that the engine should be in good working shape. Lifters are in shape, no crank play, thrust bearings look great.




I will never know whether this engine is JDM or not, but as long as it is in good shape, I guess it doesn't really matter. I mean, the lack of varnish makes it look like it's received only 3000 mile oil changes. I'll just believe that it is a JDM, based on the oil filter, and move on. Just for your reference, here is what a JDM engine exhaust looks like, and the one below is what the one on my so-called "JDM" came off of.