Engine rebuild strategies. Looking for suggestions.

[HondaDustR]

I'm not dealing with any catastrophic problem right now, but just want to get an idea of what a good plan would be for my situation.

So I'm running the standard 8v 2.5L 9.6 CR motor with about 140K mi. on it (50k of those are mine and I'm a WOT/high rpm addict ). No weird noises, good oil pressure, no headgasket leaks, but eats oil fairly quickly...about 1 qt every 500-600 miles, oil pan gasket is starting to leak but it's hard to tell just how bad it is, but there is some oil splatter all over the underside of the car downwind of it, almost every other oil seal has been done. The rest of the motor (all the external stuff) is pretty well sorted out.

I was originally just planning on doing the oil pan gasket and then rod bearings because they'd be right there already, but I'm getting the increasing notion that the piston rings are not in great shape. Stuff like strong smelling crankcase vapors, oil in the intake, and fairly recently...a good bit of oil smoke if I rev the engine before it fully warms up. The smoke diminishes as the engine warms up. Sometimes I don't even have to run it very hard to get the smoke. It kind of reminds me of exactly how this ATV that burned up the rings by running low on oil and overheating behaved before I put new rings in it. I've done a compression check several months ago with good numbers but two cyl built up pressure a bit more sluggishly than the rest. The trick is, I don't want to buy a bunch of stuff, tear into it all to find out the actual cylinder is scored and have to hunt down a new engine anyway. Besides doing rings opens up another can of worms, that being the cyl head (replacing valve guides, milling the head, possible valve job needed, etc.) This is my daily driver, so it sitting around taken apart while I go with plan B or C isn't really the ideal case, especially if I wind up with expensive parts I won't end up using.

So here's my options in order from cheapest to coolest (expensive).

1. Just let it leak and burn until it gets a lot worse, and then probably end up either building up another motor with a different shortblock or semi-longblock, or even just swapping a well sorted 8v or S.
- $6/qt plus maybe emissions testing troubles next summer.

2. Replace just the oil pan gasket + rod bearings ~$120

Only downside to this is that I'll have to hope that's where most of the oil was leaking from, hope that the pan was leaking air into the crankcase and contributing to carrying oil mist out the AOS, and pretend that the pistons/cyl walls are fine and there's nothing to worry about, except that if it is burning oil past the rings and I need to try to pass emissions next year with an oil fouled cat, replace it to pass emissions, and watch it get ruined, too, and decide I should have just done the whole 9 yards the first time to save more $$$ in the long run...if the rings really are worn.

3. Do the rings (assuming the block is fine), rod bearings, oil pan gasket, head gasket (obviously), valve guides/seals, lap the valves into the seats (can do that myself), assume the head is straight enough (since it already doesn't leak, or else have to get it milled if it isn't), other stuff that goes along with pulling the head.

~$700, EDIT: actually more like $400 plus machine shop labor for valve guides



4. Same as #3, but instead of goofing around with the original head, buying one of many944s's rebuilt heads. ~$850

optional (for #3 or #4): find a set of 10.2:1 CR pistons
- add $250-$500+. probably not worth it if it costs very much for only 15 hp.

5. Just find a solid 8v motor and swap parts to make one good one.

- $??? could be $300 or $800+. consider gaskets and such that might be needed depending on the level of unbuilding that needs to be done to the "new" motor.

6. Find a solid, complete 16v S motor (or at least one with no major problems) and just do a swap, and recoup some of the losses by selling off the old 8v parts that wouldn't work on the S motor. (<-editor's choice, but not necessarily bank account compatible ).

-$??? Anyone know what a complete S motor typically goes for?

I'm thinking this might end up being a spring or summer project for next year for whatever plan I end up deciding upon. Any more experienced engine builders and the like have any insight on this? Those that have been there before might have a better idea of what stuff goes for, cost effective plans on what's worth fixing or not, how likely the cylinders are not shot, or how hard it really is to drop in a 16v motor. Comments/input would be much appreciated! TIA

[Schumi]

Originally Posted by HondaDustR

optional (for #3 or #4): find a set of 10.2:1 CR pistons
- add $250-$500+. probably not worth it if it costs very much for only 15 hp.

I think you are looking at even less of a gain than that. think more like 5-10hp. I wouldn't do this unless you can find a set el cheapo.

If you do the rings, you can pull the head and do them that way, no dropping the crank (which means no oil pump seal replacement). This would allow you to change the head gasket while you are there(when was it changed last, if ever?). Replace the timing belt at this time too and you'll have all major service covered for the next 30,000 miles, all at the same time.

[HondaDustR]

Originally Posted by Schumi

I think you are looking at even less of a gain than that. think more like 5-10hp. I wouldn't do this unless you can find a set el cheapo.

Yeah, that's kind of what I thought. And then there's matching tolerance groups...and if they mix tolerance groups within the same engine then forget it. I do like the "decking the head down" idea I've thought about. It wouldn't be too hard to bump it up to 10.2:1 that way.

If you do the rings, you can pull the head and do them that way, no dropping the crank (which means no oil pump seal replacement). This would allow you to change the head gasket while you are there(when was it changed last, if ever?). Replace the timing belt at this time too and you'll have all major service covered for the next 30,000 miles, all at the same time.

Yes, definitely out the top. It may have had a headgasket. I heard from the PO that it had the head "done" (who, it turned out, could make up a dramatic story for just about anything, true or not). If it was that easy, then I wouldn't be so worried, but then there's all the little things that add up WYIT (wonder what the valvetrain looks like after 50k of high revving excitement on SM grade oils?). ...and just pulling the head is expensive...$60 for new hardware, $60 for the gasket, plus 8x valve guides/seals, shop labor to press in the guides, blah blah.
And the double edged blade of being an obsessive perfectionist...I wouldn't be able to sleep for months if I pulled the head and didn't do anyhting to it while I had the chance.

How durable are the cylinders on these engines, typically, assuming no abuse like leaking coolant, spun bearings, overheating, etc. ? Is there any chance that they'll get damaged if the rings wear out too much? The big thing is cost (college, other things I'd like to do besides staying home fixing the car...). If I can just drive it for another season or so and beat the rest of the crap out of it before having to dump the money, then that's just as well. If I kill the block in the process, then I might need to reconsider. There are a bunch of things on this motor I already know are working right, and it would be a pain to have to find an affordable spare, work on it, swap it, hope there's not something else wrong with it,... (I want an S engine soo bad, though!). I've got about 10k left on my belt, so there's time to get through winter and think about it.

I'm sure I'm just overthinking the whole thing and making it a bigger deal than it needs to be (as usual), but I'm just curious and like to plan stuff out. Wage the battles on my terms.

EDIT: Did some calculating and found out it would only be about $400 in parts to do rings, rod bearings, mandatory head gasket set for pulling the head, and valve guides. Machine shop labor to install the guides shouldn't be too much, and add some more if I decide to deck the head at all. Life is better now. Now I just hope it's rings passing oil and not some bad cylinders.

[Sterling Doc]

If the oil's been changed, the blocks are pretty durable. The ones of mine that burned oil did so through worn valve guides. Just something to think about.

[Schumi]

It's stuff like this where the Lindsey 3-pc crossmember sounds like such a good idea. You could drop the pan and still hold the engine in with the engine mounts and not have to supposed it from above, then take off the head and take the pistons out the top with ease.

Normally you would have to unbolt the crossmember and hold up the engine somehow as you take the head off (a big pain).

Why are you planning on doing the rod bearings? Just because you spend a lot of time up in the revs doesn't mean they are worn as long as you have had constant oil supply and quality during those times. Rod bearings for these cars aren't cheap...

[Arizona_928]

Originally Posted by HondaDustR

optional (for #3 or #4): find a set of 10.2:1 CR pistons
- add $250-$500+. probably not worth it if it costs very much for only 15 hp.

you could put lower compression pistons in and run a turbo....

[mistertate]

It might be worth it to pay somebody ~$70 for a leakdown test which will tell you a lot more about where the problem is. I disagree with Sterling Doc that the blocks are very durable. I've seen quite a few including my own with scored up alusil cylinder walls, likely due to too much carbon. Do a search on "alusil scored cylinders" or something and you'll find plenty. They usually make the same power with the scored cylinders but consume a lot of oil, like you are doing. If the leakdown says it's all past the rings you can either borrow a borescope or pull the head off and look for yourself which you'd have to do anyway if the rings are bad.
The main bearings show almost know wear at this mileage (you have good oil pressure) but the rod bearings are a good thing to do.
I would look for some of those '88 high comp pistons. Usually when I drive an 8v I'm like "damn I didn't think anything was slower than my car" but last time I drove a high compression 8v it felt just as fast as my S.
A rebuild is a fun project especially if you can do your own work and machining at school or something but unless you get the '88 pistons I wouldn't expect much of a power gain. A really good chip and exhaust help too.
Levi, what the crap? You can't do a decent turbo and add the right pistons and engine management for less than $2k.

[Arizona_928]

Originally Posted by mistertate

Levi, what the crap? You can't do a decent turbo and add the right pistons and engine management for less than $2k.

Just throwing it out there....

[Schumi]

leakdown and boroscope probably worth your time, or else you may find out like I did; I thought the motor I was rebuilding was run to hell, but after inspection the rings and cylinders were as good as new.

[HondaDustR]

Originally Posted by Sterling Doc

If the oil's been changed, the blocks are pretty durable. The ones of mine that burned oil did so through worn valve guides. Just something to think about.

Yeah, I considered that, and it could be very well the case, since I've heard the stem seals tend to break down at the spring retainer and detatch from the guides and just float on the valve after a while. Between that and worn guides, it could be not only losing oil but maybe exhaust pressure is leaking into the engine through the guides, if that's possible. Plus, the oil smoke is rather inconsistent. Sometimes it's pretty noticable and sometimes it's almost nonexistent.

For rod bearings, I wasn't expecting them to be bad, but just to replace them as a precautionary measure since they're right there once the oil pan is off, and especially if I do everything else, I don't want to have to go back in for awhile. And I definitely don't want the #2 bearing to randomly decide to go bad and destroy the rest of the engine. In the grand scheme of things, it's only $80 more.

Does anyone know if any engines ever mixed tolerance group pistons within the same block? If I could find some late pistons, I don't want to find out I need to find like 3 different kinds. Did only the 88 motors use the 10.2:1 pistons? I thought they went to the higher CR parts in 85.5 for 944's, but the 924S didn't get them until 88? Clarks garage tech info says 10.2:1 pistons were used in 87-88. Euro pistons would be sweet but probably impossible to find. If I got 10.2:1's and decked the head to make up the difference would be just as well in my book, or maybe aim for 10.9-11.0:1 depending on how much decking would be needed. It would definitely be alot less than trying to do it with 9.5:1 pistons.

Also, how often are valves reusable at this kind of mileage. If any valve stems are worn, I might as well just buy a head from many944s, unless it's just 1 or 2, which I kind of doubt if they're worn at all.


I might just try to pull the cam tower and replace just the stem seals and see what happens. That will be relatively cheap and easy, at least if the bolts don't strip. Only thing is, is it possible to remove the springs with the head still installed, maybe with one of these kinds of tools? http://www.sjdiscounttools.com/kd2078.html

Thanks for the responses, everyone!