Rebuild existing engine or replace with lower mile motor?

[M1Jenkins]

Have a 200k+ mile 944. Was my daily driver for several years and then sat on the back burner when I got into Miata's and S2000s.

I'm starting to feel bad about letting the car sit and would like to make it a weekend driver again. The problem I'm facing is that the engine just needs a significant overhaul at this point, she'd old and tired.

At this point, is it easier to just find a lower mile motor, do a ton of preventative maintenance, and swap it in? Or should I just work with what I have?

[944 Ecology]

You can do everything to the engine with it in the car except main bearings.

I would tear the engine down, make your assessment and go from there. At that point, if you have to remove the block, it will be a lot easier.

Also, nobody is going to give you much money for a 200K tired engine.

[OK-944]

M1, could you describe how your "old and tired" engine is behaving...and do you have any history for this engine and/or knowledge of how its been treated over the years?

I ask because I recently rebuilt a 165K mile engine which had not been touched prior to my pulling it apart - and what I found as I started digging was that I likely could have done a reseal instead of a full rebuild...but I went ahead because I'd never "gone the distance" and wanted the experience. What I am noticing after my rebuild is a definite uptick in available horsepower, but it wasn't exactly sluggish prior to my rebuild.

Prior to this, I'd pulled apart a (lower mileage) motor on my previous 85.5 and just did a reseal and all was well, even though it was not as "pristine" as my newer, higher mileage engine. I've since sold that car to a local auto mechanic, whose son continues to enjoy it with little additional maintenance.

You should at least follow George's advice, and start breaking things down to get a better look. If you can remove your engine and get it on a stand...great! This will make it easy to get a close look at bearings and journals (even better if you can measure these), cylinder walls, etc., plus make it easier to assess crank end-play.

If you don't want to drop your engine, then at least pull the cam housing and cylinder head to get a look at cylinder walls, valve seats, cam lobes, and lifter bores. And if you can support the engine from above, you can remove the oil pan and pull a few rod bearing caps to get a look at rod bearings and journals. You could also drop the crank girdle and crank from underneath...but would need to find a way to fully and evenly support this assembly as you did this - because the crank is quite heavy and you run the risk of stressing the girdle otherwise.

At any rate...good luck!

[944 Ecology]

Originally Posted by OK-944

You could also drop the crank girdle and crank from underneath...but would need to find a way to fully and evenly support this assembly as you did this - because the crank is quite heavy and you run the risk of stressing the girdle otherwise.

I would leave the main bearings and crank girdle alone, since the alignment and torquing would be next to impossible with the block in the car. If you screw that up, you will have a heavy boat anchor.

[walfreyydo]

Get a borescope and check your bores. If they look good you can probably rebuild. Compression and/or leakdown test would be useful to understand condition of rings/valve seats/seals.

If it were me, I would pull the motor and rebuild it on a stand. You will want to replace all seals while you are at it and its much harder to access them with the engine in the car (lower/upper balance housing seals, rear main for instance)

Used NA engines are pretty cheap as well, so if your current engine has scratched bores, you may want to find used engine with good bores. Sending the engine out to get the bores done (by a shop that can do alusil) will be expensive as it requires special equipment or sleeves to fix.

[OK-944]

To comment on the alusil “honing” process:

When I did my rebuild (87NA) last year, I was inspired by the superlative writeup from HondaDustr on this forum…to save a few dollars (and gain a bit of extra experience), to do my own “seat of the pants” cylinder bore refresh - using Sunnen AN-30 silicon paste applied to a cylinder hone to which I’d glued felt strips:



The idea behind this treatment is not to alter the inner diameter of the bores (nor do you want any cross-hatching)…but to remove the excess ring material which has been deposited between the silicon crystals on the bore walls - so that fresh silicon can be exposed to facilitate the “proper” breaking in of new rings.

But a couple of things: while my car certainly behaves like its gotten a new lease on life, including a jump in available power - I can only assume that my DIY cylinder refresh has played a part in this. While I did note that the cylinder bores, post-process, had acquired a nice semi-matte finish and seemed to hold oil a bit better than previously - I don’t happen to have a profile meter around with which to (properly) evaluate my cylinder walls on a micro-level.

Also…the silicon paste residue is very tenacious and difficult to remove. While I thoroughly taped and/or plugged off both water and oil passageways prior to using the silicon paste - if I were doing this again I would set the engine block at an angle which would help minimize the migration of silicon paste residue into other non-cylinder areas, and even then I’d do as thorough a post-process cleanup as possible.

Taking your engine block to an outfit which specializes in this kind of (alusil honing) work means that they would likely be using machinery which has been certified for this process (and would hopefully employ some degree of expertise in its use) - including procedures to accurately measure results to gauge exactly when the process is complete. But while I would also assume that such an outfit would do a thorough, post-process cleaning - I’d still want to check things over very carefully prior to any reassembly!

At any rate…however deep you decide to go with your engine - good luck!