Rebuild top end only - but how clean out case?

[MyFlat6]

Ok, so I have read several threads about rebuilding the top end only vs splitting the case and doing the bottom end as well. Based on what I have read and assuming the condition of what I will be able to assess once I start the top end tear down (condition of rod bearings, wrist pins) to gauge if the bottom end is probably healthy enough for plenty more miles (oil pressure was very good before motor was removed) I would prefer to not split the case. Splitting my 2.4 MAG case could lead to a bunch of costly machining and additional costs that come with a bottom end rebuild.

Ok, so now to my question. If I don't split the case, how can I properly clean out the bottom end since the crank and oil pump, etc will still be inside? I haven't read how others are accomplishing this in top end rebuild threads. I can remove the caps and clean out the oil galleys as best I can, but I don't think there is a way to absolutely guarantee any debris will not get in the short block when the top end is removed. I already checked with a machine shop and was told you cannot hot tank the short block.

Looking for ideas for a thorough cleaning that will not damage the internals of the short block.

[ADDvanced]

Following because I am poor and this is my plan too.

[Evans, Marv]

I've never heard of a way of doing that. The best as I understand it is to keep debris from getting into the case as you doe the tear down. I've heard of people doing a little push/pull on the rods to try to determine excess wear, but if it ran well and had good oil pressure before, I don't think there's much else to worry about.

[47silver]

Clean it all upside down so debris falls to ground plus use a shop vac while doing it
Take cam housing etc upside down. Goal is all debris falls away from motor.
Do not remove a nut or bolt until you cleaned all surfaces a couple of times.
I was very meticulous and nothing entered the case but i split it anyway as it had 84000 miles on it and i wanted to know that rod bearings, main bearings, crank would be good for another 84k. Machining was reasonsble as it did not need align bored.

[30westrob]

Good advice above. I would use a pressure washer and solvent to clean the exterior of the long block. Then be diligent about not letting dirt into the case after you disassemble the top end. I would not try to clean the oil system unless you see debris in the case. If you find evidence of debris in the case it is time to split and find out what and where. Rob

[Walt Fricke]

You note oil pressure good. That suggests that main bearings and rod bearings (and intermediate shaft bearings) are good. So why pull the rods? You can R&R rods with an intact case, but it is a pain, and you can't use a stretch gauge. To be sure, you can do a decent job with torque, or the angle method, and a lot of care.

Maybe someone has a rule of thumb about the longevity of rod bearings vs mains? But it seems that both tend to get replaced together - they live in basically the same oil, dirty or clean, environment.

The bearings which typically show the most "normal" wear are the #1 on its thrust surfaces, and the rear intermediate shaft bearing on one of its thrust surfaces. These often show a lot of copper, or brass, or whatnot in the substrate below the Babbitt metal. Interestingly, this doesn't seem to cause problems, but those are the bearings even the most thrifty and bold are apt to replace. But maybe as long as the oil pressure is good these won't cause problems before a main or rod bearing gets too thin?

What did compression and leak down tests show about the ring seal? If it was good, why pull the cylinders/pistons off? But once the heads are off that's not a big deal. And I assume you expect to send the heads off to have a valve job done?

What flavor of 2.4 is/was this? A mildly stressed T, or an S which had the pee driven out of it all its life? The 2.7s, with all the smog stuff, certainly have the reputation of needing to be align bored, and maybe spigot surfaces trued. I wonder if that is so with the 2.4s? Does it have Birals? Do those stress the head studs the way the later Nikasil/Alusils did? Didn't the Ts have cast iron cylinders, without that differential expansion issue?

I am dubious that a well treated engine, with regular oil changes, and which never blew up, is going to have dangerous particles lodged here and there in its internal oil passages. When an engine blows up, by a bearing failing or a rod bolt breaking or a valve head falling off or the like, despite the strainer on the scavenge pump, and the oil filter, very small pieces of aluminum or bearing material seem to be able to get into the oil tank, and back into the oil pump to be pumped all around. Those situations benefit by pulling some of the case oil plugs and using a bristle brush and flushing, and doing the same with the crank, often including removing plugs in the crank, and so on. Sure, you can do it on a "routine" rebuild, but isn't the effort/reward result rather different? With care, you can drill, tap, and pull the main oil gallery plugs on both ends, and run a brush through - but without being able to get at all the side passages, like the ones to the main bearings, it is hard, seems to me, to be confident no crud got pushed off into one of those, especially if previously it was sitting harmlessly as a hard coating or otherwise out of the way.

You certainly can figure out a way of sloshing some solvent around in the sump and getting it back out. I don't offhand recall finding sludge in the bottom spaces of the cases where various lips obstruct its flowing out with an oil change (absent a blow up, in which case there is a lot). And nobody bothers with this in a routine oil change, just like just about nobody fiddles with removing the oil in the front oil cooler system for an oil change. With the case split, of course, it makes sense to get all the oil out and the surfaces free of oil because handling things is much easier that way.

Maybe a better question would be the likelihood of machine work if you split the case from this model 911, mag case and all?

[Catorce]

Wow, what false economy this is. Maybe you are the kind of person that likes to do the same task multiple times.

If money is an issue, keep in mind that the only costs you would have by splitting the case over and above the top end rebuild are:

1. Bearings. And this is only a maybe because you can measure them and if they are in spec, reuse them in the same location they were in.

2. Some minor gaskets and O rings that could probably use a refresh anyways.

3. Some Loctite 574 to reseal the case.

4. New chains and ramps which I bet you need.

If the case doesn't need machining, you might only be looking at a few hundred more bucks to do it right. And you would get:

- an assurance that the bottom end was good by measuring and visually inspecting it
- a good reseal to prevent case leaks of which there are many
- peace of mind.

Really no reason to do just a top end rebuild.

[MyFlat6]

Lot of helpful suggestions here. Much appreciated. I may end up doing the whole thing but others have me very worried about splitting the case on these magnesium motors. From what I am hearing, this may add thousands of dollars depending on how much machining work is required and if the bottom end doesn't need it then not to risk splitting the case. Maybe this is not true? From what I hear, at minimum I would experct to align bore the case, then start getting into
the crank, rebuilding rods, bearings, etc - a matter of where do you now stop once you split the case.

[Evans, Marv]

You don't say how many miles you have on the engine. The bottom ends will go for a long time, and I wouldn't feel too bad about doing a top end if the mileage was under something like 50K or so. I think your chances of not having to do extensive machining on the case are decent on a 2.4. The 2.7L with restrictive exhausts have a much worse time on rebuild. However I'd listen to what Catorce said if the engine has fairly high miles. Sometimes you just have to bite the bullet.

[Walt Fricke]

Here's my understanding: The magnesium cases don't hold their shape as well as the aluminum ones do. They can distort to the point that the main bearing bores no longer line up (hence line or align bore). And with the case somewhat warped, the spigot surfaces, on which the cylinders rest, may not be flat or square - that is, all on a plane at the same distance from the crank centerline.

The engine may have been running like this, with no obvious problem other than having high mileage and maybe some loss of power. But when you take it apart, you find the main bearing aren't worn evenly (the out of alignment), and measuring spigot heights you find variances. This is where you decide to spend the money to fix these issues. Because they will only cause more trouble over time if not fixed.

On the other hand, the case may still be within spec, so no such work is done, and you do a valve and ring job, new bearings all around, and maybe some odds and ends (the while I am in there slippery slope, but for instance doing the oil passage modification Porsche did around 1976 is a cheap improvement).

You won't know where your short block is without taking it apart. So how was it running, what was the oil useage, had the power been measured, what was the mileage, and so on. And then, what led you to believe a "top end" job was in order? Leakdowns?

However, I bet you have been reading our host Wayne Dempsey's book on rebuilding 911 engines. Wayne does say that sometimes disassembling a magnesium case causes it to "relax" and the tensions from warping forces will cause it to change shape so if you were to let it sit overnight, and then put the case with crank back together, you might find the crank binding. Is that what you are worried about? Maybe one of the guys who builds engines for a living has an estimate of how often this might happen to a 2.4 with a 7R case

This is kind of back to why do you want to do anything more than clean the engine really well, change the plugs, check the valve lash (much easier to do on an engine stand than in the car), fix any leaks you can deal with without pulling the heads, and put it back in the car.

[T77911S]

i have run into the same thing with keeping it clean.
even though I have spit the case I would still keep a plastic bag over the case when not working on it.

pressure washing very well before disassembly is a big one.

I have heard of this, never done it and wouldn't so maybe someone else can verify it, but I have heard of using kerosene to flush out the inside. I HAVE ONLY HEARD OF THIS, I DO NOT SUGGEST IT.