m42 strength??

[OG2002]

hey guys i'm trying to decide what engine to use in my '75 2002. i was thinking of building a turbo set up for the m10 but i'm really considering a swap to a more modern engine before i turbo.  the info i'm looking for would be what hp level the stock internals (pistons, rods, crank) are good for. if you have experience or proof of part failure please chime in. also if anyone knows the cylinder head cfm flow and what porting will give you i would appreciate that too. thanks in advance.

[colin86325]

Apparently from what I've read the M42 is a real PITA to fit in the 2002, so not too many people choose that route

[JP 91iS]

Quote that Peerless posted on r3v:

Here is my experience with rebuilding 2 M42's. One took 3 engines to make one good one.

We will start with the factory flaws and how they should be corrected.

1) Stamped steel chain guide. These fracture and break apart. Replace with upgraded dealer part, its a all nylon/plastic construction. You will need one new 45mm long bolt in conjunction with the new guide.

2) Steel oil pressure relief valve, aluminum front cover. The steel valve can seize causing a immediate loss of all oil pressure, good by engine. Replace with updated dealer part, made of nylon/plastic. Make sure you get the spring and spacer as well. The spring is slightly longer so it all a matched assembly. You will most likely want to replace the oil pump rotors, front pump cover and bolts. All of this is about $45.

3) Front chain cover. These are known for leaking profile gasksets. The rail that holds this gasket gets corroded and leaks. Every one notices when it leaks outside the block, but no one notices when it seeps behind the block. This creates a rust cavity potentially damaging the front face of the block. Expect to at a minimum to replace the front cover. If the block is damaged, you can surface the front face to clean up any rust damage. .015" MAX.

4) Main thrust bearing. The factory in all their wisdom decided to only use half a thrust bearing shell. This is not capable of handling the high rpm loads created by the M42. You will find the bearing to be rounded and burnt black. The crankshaft thrust surface must be inspected carefully. On the 2 engines I built one crank was scrap and the other barely within spec. To correct this problem you will want to replace with a full 360* thrust bearing. I do not know if the standard replacement bearings come with 2 halfs. I use the early eta M20 main bearing set and have the lower main caps custom machined so they fit. This not only gives me a full 360* thrust surface, it also gives me a full 360* oil groove for improved oiling to the rod bearings. As a note, I pulled the oil pan on a M42 with 80K miles, it already had thrust bearing material in the pan, along with 4 oil pan bolts.

5) Crank pulley. While the stock crank chain gear does not wear very much a new upgraded part is available from the dealer. It has 2 rubber rings molded into it. This helps keep harmonic vibrations in check. This may help prevent the oil pan bolts from backing out

6) Rod bearings, I use custom Clevite 77 NASCAR performance bearings. This is a upgrade, the stock peices should work just fine as well.

7) lock-tite all your upper oil pan bolts to prevent them from backing out. This is a big problem on the front 6 bolts that surround the gasket for the oil pump pick area of the pan gasket. When these back out and fall into the pan the gasket can push out and you lose oil pressure. See number 5.

Regarding valve guides, they should be fine as they have very little side laoding due to the valve train arrangement. I did not need a cam removal tool either. When loosening and tightening the cam tower bolts, take your time, do it slow and evenly. Remember the camshafts are hollow and can break easily.

If anyone tells you the stock M42 is a great engine, they are pulling your leg or don't know the M42 very well. The stock M42 is very self destructive.

I have pictures to back up every flaw I just described above. Everything I said above comes from direct experience with the M42 engine.

Expect to pay about $2,500+ in parts and machine work to properly rebuild the M42. If you need help/advice along the way just give me shout.

Just thought I'd share that

[xwill112x]

i've always wanted a m20b25 2002...

[BeamerIS]

Could you send me those pictures?
I'm planning on rebuilding my engine before turbo'ing it