Engine Break-In Plans

[OK-944]

Net-gathered opinions are all over the map on this, but I'd like a little feedback on break-in plans for my engine (‘87NA), which I’m now in the middle of rebuilding.

This car has 170K on the clock, and was conservatively driven and extremely well maintained by the P.O. All crank and rod journals are mirror-smooth, and well within specs. Cylinder walls have a slightly semi-matte looking texture, are light grey in color, and scratch-free. When I’d described them to a guy at Lindsey racing, he suggested just a wipe down with some automotive laquer thinner would likely be fine.

Had there been evidence of prior neglect or mistreatment, and/or if I did not have complete records for this car going back to day one, then I would likely have invested in some good measuring gauges to verify all O.D./I.D. specs. Actually I did check all of the journal O.D.’s with my measuring calipers (all were well within specs), but did not directly measure cylinder I.D.’s. I did, however, use Plastigauge to check check bearing shell to journal clearances, and all was well.

With my understanding that Glyco rings are “pre-spec’d” during manufacture, I trusted that this would allow me to then check the cylinder I.D.’s and tapers (not through actual measurements, but by tolerance) by checking ring gaps at several depths of each cylinder. I went ahead with this, and, as with the bearings, all cylinders seem to be well within spec, with almost no evidence of taper. Again, I would not have trusted this if things did not otherwise look pristine, nor would I had there been any previous issues of excessive oil consumption or lack of compression - or over-compression in the case of excess carbonization…but piston-heads and valves were relatively clean.

My plan for engine break-in is to first top the engine up with a decent non-synthetic oil, likely 10W40, and add to this some Lucas Break-In Additive. I’ll start the engine and hold the RPM’s at around 2000 for about ten or fifteen minutes, then shut the engine off for a bit. Then, I’ll take it out for a spin to set the rings - with a number of intervals (around 10?) of brisk acceleration/deceleration, aiming to keep RPM’s between 2K and 4K during this time. I’ll then allow the car to idle a bit and then change out the oil and filter, once again using the same non-synthetic/Lucas additive mix.

After the above, I will drive the car “normally” for about 150 miles, after which I will, once again, change the oil and filter - using the same non-synthetic oil, but this time without the Lucas additive. I’ll then drive the car about 500 miles, then, again, change out my oil and filter…but this time I’ll be going back to my favorite Mobil-1 (synthetic) 10W40 “High Mileage” formula. Yes, I know that some of you may cringe at this, but this oil has worked well for me, and after having taken apart two 944 engines after having run this oil for thousands of miles, I can see no evidence of any deleterious effects from having used it. Lots of folks also recommend either 15/50 or 20/50 for this car, but for my conservative (mildly spirited) overall driving habits and northern Vermont climate, the 10W40 seems to work fine.

At any rate, sorry for being so long-winded…and I would welcome any feedback on the above. While I’d previously done an engine-out reseal (on an 85.5), this is the first time I’ve done a full rebuild, and I really want to do what is best for this engine. Thanks!

[IdahoDoug]

So, clarify what you are doing here. It sounds like you are changing no internal parts whatsoever except the rings? I base this on all crank and rod bearings checked with plastigage and found satisfactory and you bought only Glyco rings.

If so, all you are asking about here is "how to seat the new rings in my 944 engine". I know how to do it with conventional engines but this engine has a special cylinder wall material.

Personally, I'd call the Lindsey Racing guy back and ask him if he's confident enough to recommend wiping the cylinder walls down with something.

[OK-944]

To clarify - replace rings, all bearings (crank, rod, balance shaft), clean head, check springs, valves, guides (replace as necessary), lap valves (gently as faces/seats are already pretty good), complete reseal of top, bottom and front of engine. Lots of other work also (breaks, wheel bearings, etc.etc).

I had a long conversation with Mike at Lindsey Racing awhile back, during which I described to him as best I could my visual assessment of cylinder wall condition, plus reflected on my car's (complete) history and the fact everything within this indicates that the car was never really stressed in any way. Mike then suggested that it would likely be ok if I simply wiped the cylinder walls with some automotive laquer thinner, and proceed from there.

Mike also gave me his engine break-in "recipe," suggesting a succession of oils, starting with Joe Gibbs BR (break in) oil. We also chatted a bit about oils in general...and I mentioned that after having taken three of these engines apart, I'd never noticed any obvious deleterious effects from having used Mobil-1 10/40...that with my driving habits and location (northern Vermont) this oil has worked well for me and I'd continue to use it after having first broken in with a non-synthetic.

I had spent some time earlier trying to find someone with a profile meter to "properly" assess my cylinder walls, plus someone with a shop capable of doing whatever honing might be indicated to bring the walls back into spec. I could not find such a shop within any sort of driving distance, the most likely one, Fast Attack Motor Sports, being located in Eliot, Maine, about three hours drive from my house. Repeated emails and calls to them have gotten no replies.

I then considered doing this honing myself, based on Honda Duster's truly excellent treatise on this subject...but reconsidered (wisely, I think), as I have never honed a cylinder in my life. Further research relating to others experiences of not honing as part of the rebuild process, at least in cases where cylinder walls are in good shape and exhibit the slightly mat-finish texture, and middle gray color, as do mine, convinced me that I could get away with not honing. My conversation with Mike at Lindsey only reinforced this - and my decision has been made irrevocable as I've already installed the crank. All crank journals mirror-smooth, and based on plastigauge they are all exactly in the middle of spec tolerances, as are all ring gaps when measured at three locations in each cylinder bore.

So...I think I'm good to go. My only real concern is based on my assumption that there is no way that my cylinder walls are absolutely ideal, and that I need to do what I can to help my new rings set as best they can with whatever silica might still be exposed.