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Thread: Let The M73 Swap Begin!

  1. #26
    Join Date
    Dec 2013
    Location
    San Antonio
    Posts
    153
    My Cars
    850i, '76 2002, '76 530
    I would suggest changing cam seals and front/ rear crank seals while you have it on a stand.

  2. #27
    Join Date
    Dec 2007
    Location
    Dallas, TX
    Posts
    9,852
    My Cars
    '93 850Ci- Daily Driver
    Don't touch the headgaskets unless they NEED replacing. Personally, I would put in new valve stem seals (this is really easy in an engine-out situation). Another one would be the rear main seal, as well as upper and lower oil pan gaskets. Cam chain tensioner o-rings are also a good candidate. I would also time the cams. Distributor base seals and water pipe o-rings. Do not mess with the valley cover gasket unless it is currently leaking - those mounting studs snap fairly easily. Other than that, just take a good look at everything as you go along.
    '93 850Ci - Mineralweiss Metallic
    ALPINA B7 -Alpinweiss III


    ...the price of cool ain't cheap!

  3. #28
    Join Date
    Jul 2009
    Location
    Del Mar, CA
    Posts
    683
    My Cars
    2001 740i sport, 91 850i
    I have replaced the valley pan on 2 91 motors and broke 1 bolt on the first and 3 on the 2nd. In all cases the bolts broke close to the head and left plenty of exposed shank after removing the cover. With a bit of work I was able to unscrew them all. It is a lot easier to deal with a broken bolt with the engine on a stand as opposed to leaning over a fender. Despite the warnings I would do it now to avoid having to deal with it later. Also the cover at the rear of the block. The problem with all of these is coolant seeps into the bolt threads and corodes them. I think the later engines used better quality (galvanized) bolts and are less prone to corosian.

  4. #29
    Join Date
    Aug 2013
    Location
    AZ
    Posts
    314
    My Cars
    1998 BMW 750iL
    I think replacing the spark plugs as part of the preventative maintenance is a good idea. Replacing them while the engine is in is a headache, especially when you get to the last 4 spark plugs. I went with NGK on mine due to reviews from other m73 owners and their preference over Bosch.

  5. #30
    Join Date
    Aug 2007
    Location
    Duesseldorf, NRW, Germany
    Posts
    6,813
    My Cars
    '90 850iM70B54, '91 850i
    Quote Originally Posted by dragon850 View Post
    M73 direct transplant with proper tuning is the way to go. dont mess around with M70 heads.
    mess around? There is no mess with using M70 heads. And I quite honestly see no advantage in using the M73 heads but am happy to learn.
    A pure M73 swap is certainly easier (except the exhaust issue) and I've done it a few times as well. Performance wise the M70B54S is way ahead though.
    You basically get CSi performance versus standard M73 performance. And the cost of the Schrick cams versus custom made downpipes is IMO not a reason to say NO.
    If someone has a budget that tight i recommend to stay away from such a project in the 1st place.

  6. #31
    Join Date
    Aug 2007
    Location
    Duesseldorf, NRW, Germany
    Posts
    6,813
    My Cars
    '90 850iM70B54, '91 850i
    Quote Originally Posted by TxGR8White View Post
    The slight gain in HP using the M70/Schrick combo, is not worth the extra work in my book. Also, the camshaft oiling spraybar on the M73 is 1000x better, and let's not forget the M73 has roller rockers. I agree with you, change out the front lower timing cover and just drop that baby in. You will be just as happy(especially with the 3.91),with a lot less work. I do the same thing: when I want a kick in the pants, I climb into the cockpit of the B7.
    375HP versus 326HP is just a slight gain in your opinion? OK, maybe a personal thing. And what's so great about the roller rockers? I've seen broke ones but never saw a really broke rocker in a M70 head - only worn ones.
    And the oil feed pipe in the M70 heads are absolutely OK as long as the banjo bolts are in place. What it comes down to IMO is saving the job of replacing heads with all related work, time and expenses versus getting 50 extra ponies.

    - - - Updated - - -

    Quote Originally Posted by TxGR8White View Post
    Don't touch the headgaskets unless they NEED replacing. Personally, I would put in new valve stem seals (this is really easy in an engine-out situation). Another one would be the rear main seal, as well as upper and lower oil pan gaskets. Cam chain tensioner o-rings are also a good candidate. I would also time the cams. Distributor base seals and water pipe o-rings. Do not mess with the valley cover gasket unless it is currently leaking - those mounting studs snap fairly easily. Other than that, just take a good look at everything as you go along.
    100% agreed. Exactly what I'd recommend as well.

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