Im planning on buying a used m20 for cheap and doing a complete rebuild cause im the teaching urself kinda guy but ive never rebuilt an engine. Can i get a list going of does and donts and wat i should definatly replace.
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do: replace everything other than pistons, crank, and rods IF they're within spec. ninjaedit: and the cam, too if you're just rebuilding to stock specs.. make sure that isnt pitted and has no flat spots or unusual wear.
don't: skip on machining, reuse bearings, main cap bolts or rod bolts, or take short cuts.
do: take lots of measurements to make sure everything is within spec
don't: use a tape measure to take measurements.
Go spend some time on E30tech and read through some of Peerless's rebuilds. He is a great engine builder and you can learn a lot from his threads.
Good luck! I'm glad to see more people pay attention to the M20-Alex -
If you are going to do a good rebuild of an engine you will need micrometers that can measure to a ten thousandth of an inch for the crank and a bore gage of the same resolution for the cylinders. Since those measuring instruments aren't cheap you should find a good machine shop that can do the measurements.
In addition to checking crank journals for wear one needs to know that BMW bearings come in several dimensions to accomodate variations in manufacture. One measures the crank journal diameter and picks the "color" of bearing that provides the correct clearance. In some cases it is necessary to use more than one "color" of bearing in the engine. You will also need to check the cylinder bores for wear and if worn beyond spec the cylinders need to be bored and oversize pistons installed. If the cylinders are okay, they need to be cross-hatch honed and the pistons checked for ring groove wear. Whether used or new pistons are used, the ring gaps will have to be checked and possibly adjusted. And wrist pin tolerances must be checked and the rods rebuilt or replaced if out of spec.
In addition to the crank and cylinders, a new oil pump and pressure relief valve should be included in any rebuild. It goes without saying that all seals need to be replaced and the head needs to be rebuilt, which may mean new guides, rockers, exhaust valves, or even springs or the cam. I always have a minimum surfacing cut done on any used head to eliminate the warp. New head and rod bolts are madatory, but I won't re-use main bolts either.
The cost to do this right, assuming the cylinders aren't worn, exceeds (by a generous margin) the cost of a good used engine. If the cylinders are worn and a rebore needed, the cost of the pistons alone is as much as a good used engine. If you are doing as a learning exercise, the cost may be a worthwhile investment. But if you see the exercise as a way to get by on the cheap, that isn't gonna happen.The car makes it possible, but the driver makes it happen.
Jim Levie, Huntsville, ALComment
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i have access to those tools but im not sure wat the specs are got any links for me?Comment
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Find a E30/vintage specialist in your area and see if you can be a shop grunt in exchange for guidance. Better talking to a knowledgeable person IN person if AT ALL possible.Comment
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Originally posted by kcoelhoe30 View PostThe car makes it possible, but the driver makes it happen.
Jim Levie, Huntsville, ALComment
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