Considering engine rebuild, need advice.

[fyberoptic]

Hi, I have a 1994 318iC with about 175,000 miles on it. Currently the only work i have done to the engine/drivetrain is install a new timing chain tensioner and I installed a new clutch. It feels like the engine is getting tired and I was wondering how much money I would be expecting to sink into the engine to rebuild it. I have not performed a compression check on the engine but I do regularly change the oil with full synthetic.

[bflan2001]

first check your compression. if you have good compression i would leave the bottom end alone, that's a LOT more $$ for something that likely doesn't need to be done. i'm in the middle of a rebuild (minus bottom end), here are some of the essentials:

timing components (sprockets, guides, chain, etc) - 500
gasket kits - 200
head rebuild - 400-500
water pump, thermostat, plastic coolant manifold & hoses - 150
silicone vacuum hose kit - 100
oil filter, air filter, spark plugs, belts, sensors - 100
oil pressure relief valve - 30

Other possibilities:

transmission seals - 15
transmission mounts - 20
motor mounts - 200 (or 20 for standard rubber mounts)
fan clutch - 70
driveshaft guibo & center support bearing - 100

[DesktopDave]

I'd go over it before you decided on a rebuild.  Good time to budget a stroker build...not too much more effort than a proper rebuild.

I had a lot of little problems with mine that made it feel down a bit...little stuff like intake vac leaks, old injectors, O2 sensor, spark plugs.  Runs great now, @284K miles!

[bflan2001]

i wouldn't think too hard about a stroker build. i've been searching for a crank for a couple months with zero luck. i'm changing my build now to a turbo build because i want to get it done and all i'm waiting on at this point is the crank. i did find one guy on a forum selling them from europe, but i can't send a grand to a stranger in another country and keep my fingers crossed.

so onto the turbo build! if i do happen to find a crank in time (and i'm not broke by then) i guess it'll be a turbo stroker, but i won't hold my breath.

edit: when i say 'search', i mean i've been emailing & calling multiple shops in the US and Europe, searching all the ebay sites, forums, etc. and on top of that, i have two people in the UK searching, one in the netherlands, and one in germany.

[Warsteiner]

So go down to the local BMW stealer and order a crank. You get 20% off for being  a BMWCCA member. I bought mine for $800. Then you don't have to worry about what you're getting, from whom and when. That's your safest bet!  Well worth it in the end to have peace of mind.

Cheers,
~Ralph

[Gerta318is]

Ralph, what all goes into making a stroker build for the M42?  Is there a downside to doing it with a high mileage engine?

[bflan2001]

the essentials are a euro diesel crankshaft from the m47 & custom pistons. but to really get the power out of it you'll want to do a lot more (headwork, injectors, clutch & flywheel, intake, etc)

[Gerta318is]

What does all that cost roughly?

[Warsteiner]

There is nothing wrong with a high mileage motor as long as you replace all the parts needed to make it fresh. The more seasoned the block the better! Back in the day they would use high mileage blocks, like 100K, due to the fact of all the heat cycles it's been through and they knew that the block, "metal", is now conditioned and won't change shape, warp, etc....

So just get a parts list together and go for it!! All new gaskets everywhere, new chain, oil pump parts, water pump, check your gears and rails etc...

My recipe is S50 pistons shaved 2.65mm, dished and reliefs cut for 10.85 compression. Use 138mm aftermarket rods and the small end needs to be honed to fit the 22mm S50 piston, with the M47 diesel crank that has the nose turned down to fit the crank gear and a new keyway cut.  

The secret is the rods. Trying to keep the longer length but still making up the difference to use that piston.  Try looking in the world of B18C GSR. It's a perfect fit! If you use the S52 piston then you shave off even less and gain more displacement, 86mm vs 86.4mm.

I'll have a complete write up once my car is finished. I'm in Thailand now getting married, honeymoon etc..... Should be done in Dec.

The cost is not cheap. But then again how far do you want to take it. Head porting? Exhaust, muffler? Cams, litters? Engine management, hard chip?How much of the work can you do yourself too? It's really hard to speculate but maybe someone who bought one can chime in? I built my own and didn't want to really keep track. There are so many costs that pop up when you least expect it. Lol.

Cheers,
~Ralph

[bflan2001]

Ralph, I've been thinking about longer rods instead of the 135 rods everyone recommends. 135mm rods leave you with a rod/stroke ratio of 1.53:1, which really isn't very good. Longer rods would yield a much better rod/stroke ratio. From what I learned in my Honda days, ideal R/S ratio is 1.72:1 or something close to that. I'm just worried about the side-load force with such a short piston. My knowledge is pretty limited in that area so I have no idea how to calculate things to see if it will work. I will be keeping an eye on your build and if the 138 rods work for you I will definitely do the same.

[wazzu70]

There is nothing wrong with a high mileage motor as long as you replace all the parts needed to make it fresh. The more seasoned the block the better! Back in the day they would use high mileage blocks, like 100K, due to the fact of all the heat cycles it's been through and they knew that the block, "metal", is now conditioned and won't change shape, warp, etc....

So just get a parts list together and go for it!! All new gaskets everywhere, new chain, oil pump parts, water pump, check your gears and rails etc...

My recipe is S50 pistons shaved 2.65mm, dished and reliefs cut for 10.85 compression. Use 138mm aftermarket rods and the small end needs to be honed to fit the 22mm S50 piston, with the M47 diesel crank that has the nose turned down to fit the crank gear and a new keyway cut.  

The secret is the rods. Trying to keep the longer length but still making up the difference to use that piston.  Try looking in the world of B18C GSR. It's a perfect fit! If you use the S52 piston then you shave off even less and gain more displacement, 86mm vs 86.4mm.

I'll have a complete write up once my car is finished. I'm in Thailand now getting married, honeymoon etc..... Should be done in Dec.

The cost is not cheap. But then again how far do you want to take it. Head porting? Exhaust, muffler? Cams, litters? Engine management, hard chip?How much of the work can you do yourself too? It's really hard to speculate but maybe someone who bought one can chime in? I built my own and didn't want to really keep track. There are so many costs that pop up when you least expect it. Lol.

Cheers,
~Ralph

Ralph, congrats on getting married and have fun in Thailand. Always wanted to go there myself. Im getting married in March so I am nearly in the same boat.

Your build sounds pretty sweet, cant wait to see the results!

[E36-italia]

There is nothing wrong with a high mileage motor as long as you replace all the parts needed to make it fresh. The more seasoned the block the better! Back in the day they would use high mileage blocks, like 100K, due to the fact of all the heat cycles it's been through and they knew that the block, "metal", is now conditioned and won't change shape, warp, etc...

Are you referring to the turbo M10's from back in the Turbo era of Formula 1?
If so, Racecar engineering (or professional motorsport world.. can't recall) did an article about that... according to RCE the bmw engineers tried a junkyard engine back in the day...it blew to pieces right after start up ;-)

Another issue with high mileage engines is that the metal in the block goes soft... due to nr. of heat cycles and sometimes overheating.
As far as i know (and that's not much) a head warps, yes because it got to hot, but it stays in banana mode because the metal turned soft (ie: not getting back into shape)

As for the original topic starter:
Depends how you see your car (daily? track toy? etc.) .. and what you want to do with it ..or in other words: how long do you think you keep it?
if your car is just for sunny weekeds then yes, maybe you can justify the expense vs joy in return... but for a car that brings you to work and back, then prob. you won't keep it for another year or two (guessing here )
If thats the case: you'd sink in more $ then you get back from it (selling or fun.. or both)

It all depends on what you like to do with your car!