poor mans rebuild? or swap?

[!kid]

so after trying to figure out a oil consumption problem i believe its come to this.
my m20b25 was needing oil way to often and fouling spark plugs did a compression test twice numbers came out good. found a broken valve guide replaced head with known good one, new valve seals,head gasket and spark plugs. ran good for a few days but sounded like i had a massive cam! redid my valve adjustment. sounded better. pulled out a spark plug just to have a look see and found a wet oily plug :( when i hold rpm above idle you can hear it misfire.
the clean intake manifold i installed now has oil stains in the runners.

so hears my idea....
with my budget i cant afford to have a shop to do the rebuild so i would be using used pistons a spare block and spare crank i have laying around with new rings,rod and main bearings.

what are your thoughts on my rebuild idea?

again because of my budget i am pretty much limited to pulling a motor from a yard car. unless i can find a motor for dirt cheap.

M50TU swap?
M44 swap?
M20 rebuild?

[MR 325]

If you're on a budget, rule out the M50 swap. (And M44, wtf why?)

Smartest thing to do would be buying a known good used engine, maybe from a forum member. Swap complete engine and part out your old engine.

Otherwise, I have a good short block I'd sell cheap if you want to go that route.

[!kid]

after i posted i did some math and looked up replacement parts for an M50 ... yeah cant afford that shit lol

i am a fan of DOHC 4cyl what can i say... the sound of an M20 going flat out is music to my ears too

its going to cost me around 450$ to rebuild. hmmm maybe one way of looking at it is.
if I am going to do a rebuild, do it right or don't do it at all. it will more or less just be a band aid?

[StereoInstaller1]

Sounds to me like you get to learn how to use plasti-gauge and a ring gapper...

[jlevie]

Comparing the results of a dry and wet compression test and getting leak down numbers will tell a lot about the condition of the cylinders and head. When the mileage on the engine is factored in you can make a pretty good guess as to what would be needed to rebuild the engine.

In the best case, which can happen with lower mileage engines, the cylinder bores may have negligible wear and a set of rings and bearings may be all that is needed. But by the time oil fouling is present on the plugs the odds are that a rebore and new pistons are needed. You can't tell for sure until the engine is torn down and the bores measured. But based on mileage and test results you can make a pretty good guess.

If a rebore is needed the economics favor replacing the engine with lower mileage one from a salvage yard. The cost of new pistons ($500-600) is about what a good used engine will cost. And by the time machine shop costs are added in the used engine will be cheaper. The advantage of rebuilding an engine, even though it will cost more than a used engine is that the rebuild will zero time the engine. Meaning that it is then good to go for another 200k. Which path to take depends on available funds and how long you plan to keep the car.

Something else to consider is that to properly rebuild an engine you need to have, or have access to, about $1200 worth of precision measuring instruments. Cylinders, pistons, journals, etc require dimension checks accurate a tenth of a thousandth (0.0001").

[!kid]

i called up E30 motor werks and asked Robert a ball park price. to do a rebuild the right way its going to cost about 2000$:loco: I know he does top notch work and knows the M20 very well. but i cant afford that.

dont plain on using the block,pistons/rods,crank. thats in the car if i do a rebuild. I'll be using a spare block, crank,pistons/rods that i have that came out of a good running car. I've measured the crank its all still with in spec, as well as the pistons. (i own a 2-3 mic,dial calipers)


whats wrong with using old pistons even if the check out good ?
do i really need to buy new ones?

[jlevie]

Do your micrometers measure to a tenth? Common micrometers are only good to a thousandth.

Bearings come in three grades with about 0.0002" between grades. You measure the journals and pick the grade of bearing that fits the journal dimensions. This is done to allow for the inevitable variation in manufacture, not specifically to compensate for journal wear. To do it really right, you measure the bearing diameter with a bore gauge and swap bearings to achieve a clearance of 0.001 per inch of journal diameter. That may mean using bearings from all three grades in one engine. While this level of attention isn't necessary for a street engine, it is pretty much routine when building a race engine.

Cylinder bores need to be measured at multiple points around the diameter and at the top, middle, and bottom of the bore. That is done with a bore gauge that has 0.0001" resolution. Pistons don't require quite as much precision in measurement, to 0.001" is okay. The reason for measuring the pistons is to make sure the skirts aren't worn, which will cause piston slap. It is important that the ring grooves in the pistons aren't worn. That is checked visually for rounding and measured with feeler gauges.

New pistons are required if the cylinders have to be rebored, if the skirts are worn, or if the ring grooves are worn. In general, a lower mileage engine will have good pistons if the engine hasn't suffered a serious overheat. A high mileage engine almost always has worn bores and that can only be fixed by reboring, which means new pistons. If the cylinders are within spec, they need to be honed to re-establish the cross hatch so that the new rings will seat. The cross hatching holds the oil needed while the rings wear in.

A pro will know to do it, but most DIY'ers aren't aware of the importance of checking, and perhaps adjusting, piston ring gap. That is done by squarely seating the rings in the cylinder and using feeler gauges to check the gap. If the gap is too small you file a bit off the end of the ring.

One other bit of advice. Don't have the block hot tanked. Doing so will destroy the intermediate shaft bearings. Those aren't easily replaced. The bearings are available, even though they are listed as NLA. But they have to be reamed after installation which requires custom tooling.

All of this may sound a bit intimidating and difficult. But it really isn't all that difficult. You can do a quality rebuild of an engine in your garage. You just have to have the measuring instruments and the patience to do the job right. Understand that the parts and machine work will wind up costing about as much as a used engine, and that is if you don't need new pistons and/or a rebore. But then you'll have a zero time engine as opposed to a used engine.

[!kid]

my mic's only read .001 inch. thanks for your post Jlevie, I am familiar with the most of the basics on machining and rebuilding an engine from school,past job, and a lot of reading online/books. I've just never rebuilt an engine by myself. Plained on buying the bearings/rings from Pelican Parts. for the main bearings they only have two STD sets to select from one for pre 2/88 and another for 3/88-91.

my plan for the rebuild is, buy a couple more tools so i can measure the cylinder bore and main bore and adjust ring gap, lightly pass a ball hone through the cylinders, measure everything the best i can to check that its within STD spec, plasti-gauge the main and rod bearings.

your thoughts?

[jlevie]

Plasti gauge is nowhere nearly accurate enough for this. Pelican, and most other on-line vendors only offer standard (aka yellow) dimension bearings. Your dealer can get the other two grades if measurement of the journals indicates that you need the slightly larger bearings. There is a table in the Bentley manual that shows the journal size range for each bearing ID. You will need a 1-2" and an 2-3" tenth reading micrometer to check the journals. You can get SPI micrometers from MSC and other industrial suppliers for not a lot of money.

Unfortunately the entry price for the bore gauge you need for the cylinders is about $350. The more economical alternative is to have the shop that cleans & cross hatch hones the block check the bores. Proper cross hatch honing can only be done on a machine that controls rotational speed and vertical travel. You can't do a satisfactory job by hand.

[ckarsonkidd]

i say m20 rebuild im doing the same i had the same exact problem

[acolella76]

too many people on here thing they know how to rebuild engines and once they put the engine in the car they find out that the engine they built is much worse than the engine they had. Not trying to insult you, but just make sure you know what you're doing. I prefer a rebuilt m20 over 24v swap any day