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The elusive 224/3.7 MerCruiser banger

Discussion in 'The Hokey Ass Message Board' started by tjm73, Apr 9, 2008.

  1. tjm73
    Joined: Feb 17, 2006
    Posts: 3,380


    That bell with the slanted mount is from an 80's/early 90's F-body. Some enlightening tech there.

    So that truck bell mounts up without modification and has not interference issues?
    Last edited: Oct 18, 2019
  2. Yes, no interference with any engine or transmission parts. Modification is absolutely not required as long as a starter without an extended nosepiece is used. I cut a hole for the end of the big old standard Mercruiser starter in this bell housing and later used it with a much smaller gear reduction starter.
    The smaller starter saved about 10 lbs. I posted photos of the opening I cut some time ago. You can see that their location impacts nothing except the starter nose.
  3. tjm73
    Joined: Feb 17, 2006
    Posts: 3,380


    Good info to know. Thanks for sharing.
  4. They are available and should be cheap. A bystander laughing said "Do you know what you just bought?" but in-spite of my ignorance the big ugly bellhousing worked out very well. It just bolted in and worked from the beginning. it is a gmc #6263756 and fits 1973 to 1981 trucks. Other than an extra bolt hole at the top, It has the identical rear bolt pattern and the same front pattern as the car transmission. its length is the same as the other chevy transmissions. It is just has more room for a larger flywheel.
    Last edited: Oct 21, 2019
  5. qUOTE="tjm73, post: 13289160, member: 11975"]That bell with the slanted mount is from an 80's/early 90's F-body. Some enlightening tech there.......cut
    enlighten me as to the advantages of it, I only see a Saginaw transmission being impossible to drain tilted over like that and leaking oil on its left side a shift linkage would be difficult. They must have had their backs to the wall. Hydraulics to move the fork are an improvement.
    Last edited: Oct 19, 2019
  6. tjm73
    Joined: Feb 17, 2006
    Posts: 3,380


    I have no idea. I'm a Ford guy. I just know that GM tilted them for some reason. I think it might have been something to do with floor clearance.
  7. Dealing with component fit:

    A friend (now 96) told me that, in the past, it was common to need spacers at the pilot bearing. I read that it is presently common to use spacers behind hydraulic pilot bearings to prevent over extension failure. This problem is new to me, I have a 36 mm gap to fill between my (long) pilot bearing and a clutch disk which normally requires a short pilot bearing.

    The clutch end of the center of a pilot bearing does not spin on the "snout" of the bearing retainer and the opposite end of the center of a pilot bearing is often blocked from spinning on the "snout" .

    A simple metal spacer between the clutch fingers and the pilot bearing would spin on the bearing retainer, causing wear that would make clutch disengagement difficult. A high density polyethylene spacer with its soft slick surface should not damage the bearing retainer. I tried melting plastic jugs ( it is the right plastic type) into a tin can for a spacer but it takes a number of jugs and a surprisingly long time to do this. (It slowly melts at 350F.) It is far easier to just buy what you need. Don't try using old plastic as it loses its plasticizer over time.

    As a short throwout bearing is about the right size for a spacer it may be possible to attach one to the rear of my long throwout bearing. I was advised not to weld it because of potential warping and cracking issues .

    The fit is not due to bellhousing length, I compared several and they are identical in length.

    To cure a modest gap , longer adjustable clutch fork ball studs are available. The newer ones have a different thread than the old ones. To adjust the throwout bearing location more than that, a new ball stud will have to be made but it is not hard.

    Any advice is welcome.
    Last edited: Oct 20, 2019
  8. ^^^ Holy sh*t !!! That bellhousing is gorgeous.

    I've often looked at this thread, for inspirations. The stuff done here, is needle moving. Love it.

    Pictures saved, in case the that guy's thread disappears ...









    Last edited: Oct 22, 2019
    Dannerr and Old Dawg like this.
  9. tjm73
    Joined: Feb 17, 2006
    Posts: 3,380


    The guy that did that owns Gearbox Grannies. They build V8 swap stuff for RX7's.
    Old Dawg likes this.
  10. This afternoon I cut the bottom out of a 153tooth Chevrolet bellhousing to be able to get a stock mercruiser flywheel into it. It was an experiment.
    In post 2040, it is the one with a dab of yellow paint on it. A big chunk was removed (2 inches by 12 inches). Flywheel teeth are still in contact with the aluminum so more remains to be cut away. The aluminum of these bellhousings is a strong alloy but it is thin, brittle, subject to cracking and must withstand the full torque of the engine without breaking. With a large hole in it, that part of it changes from a "tube" structure which has strong resistance to twisting forces to a partial tube which is much weaker . In my opinion a 153 tooth bell housing is too small for use on a 3.7 mercruiser engine but you can use them on the smaller 120 and 140 mercruiser engines
    Last edited: Oct 29, 2019
    kidcampbell71 likes this.
  11. GearheadsQCE
    Joined: Mar 23, 2011
    Posts: 2,513


    Can you back up a little? I thought you had previously built a combination of Mercruiser Engine, Chevrolet bell housing and GM gear box.
    What flywheel/bell housing did you use in that set-up?
    What is different this go round?

    I have Chevrolet aluminum bell housings for both the 153 tooth and 168 tooth flywheels. I can measure the diameters of the flywheels for those tomorrow.
    What is the O.D. of the Ford/Mercruiser flywheel?

  12. Bruce,

    You have solved one of my questions if there are different bell housings for the 153 and 168 tooth flywheels. Could you provide a vertical measurement from the inside of the doghouse peak to the inner floor of those two bellhousings?

    Thanks for helping me work through this.

    As measured the Mercruiser/Ford flywheel is 34 cm outside diameter on the ring gear teeth.

    Yes, I did this before :
    #1. Allis Chalmers engine/ Chev 168 tooth flywheel/ Chev truck bellhousing/ GM transmission
    #2. Mercruiser 3.7 engine#1 / Mercruiser-Ford flywheel/chev truck bellhousing/GM transmission
    #3. Allis Chalmers engine/Chev 168 tooth flywheel/ chev bellhousing / GM transmission
    #4. Mercruiser 120 engine /Mercruiser-chev flywheel/chev car bellhousing/GM transmission
    #5. Mercruiser 3.7 engine#2/ Mercruiser-Ford flywheel/chev truck bellhousing/ GM transmission

    In every case the transmission was any one of several Saginaw 3 speeds
    (I began with a pickup Saginaw 3 spd and found it was useless except for its bearing retainer.)
    The chev truck bellhousing was the very same bellhousing.
    The Allis Chalmers engine was the very same engine.
    I made an adapter plate to connect the Allis Chalmers engine to a chev bellhousing
    I was surprised that #5 did not just bolt together as the others had done.

    numbers 1,2,4 and 5 are for different engines in the same car over several years
    number 3 is a completely different car
    numbers 1& 3 were the same engine/flywheel/bellhousing

    I remember needing an extra long clutch fork ball pivot long ago, for #1 or 2

    My problem was in purposely mis matching the clutch disk and throwout bearing. It fits now with a matching bearing and disk as I made a longer ball stud.
    Last edited: Oct 28, 2019
    Old Dawg and kidcampbell71 like this.
  13. GearheadsQCE
    Joined: Mar 23, 2011
    Posts: 2,513


    I have a 3899621 bell housing. It measures (inside) 16" from top to bottom. All my other ones measure less than 15".
  14. GearheadsQCE
    Joined: Mar 23, 2011
    Posts: 2,513


    Somehow the rest of my post didn't make it.
    The 153 tooth Chevy Flywheel measures 12 3/4" dia.
    The 168 tooth Chevy flywheel measures 14 1/8" dia.

    The Ford/Mercuiser is just over 13 3/8" dia. if I did the metric to inch conversion correctly. Should work in the 621 bell.
  15. Yes, the Mercruiser 3.7 flywheel is to large for the common small chevy bellhousing. I cut up one of the smaller bellhousings to get it in and it still drags on the bellhousing. My cut is now two inches deep and a foot wide across the bottom center of the bell housing it is a big hole and that makes it weaker.
    Last edited: Oct 25, 2019
  16. GearheadsQCE
    Joined: Mar 23, 2011
    Posts: 2,513


    What bell housing did you use in example # 2 above?
  17. Chevrolet pickup bellhousing #6263756
  18. GearheadsQCE
    Joined: Mar 23, 2011
    Posts: 2,513


  19. It is aluminum out of the 70's . Exact same engine bolt locations, but it has more room inside it for a large flywheel and pressure plate.

    However I also have a half circle cast iron bellhousing from the 1950 period. I bought it because it has a starter mount on the bottom of it which might solve problems if one encountered clearance issues with a starter.
  20. GearheadsQCE
    Joined: Mar 23, 2011
    Posts: 2,513


    Is there a number on the truck bell housing?
  21. yes there is a number on the bottom of it, #6263756
    there are 3 sizes of bell housings this being the largest 153t, 168t and truck.
  22. BIGDOG69
    Joined: Jul 6, 2018
    Posts: 21


    Has anyone put an automatic trans behind the 3.7? What mods were needed? I'm an old fart who doesn't want to shift gears anymore. Retired long haul trucker with almost 4 million miles under my butt!
  23. I just made a long ball stud cutting up two ball studs and joining them with a short length of 3/8" black pipe. The ball studs are so hard that nothing but abrasive can cut them so anneal them first. Getting the length right is a cut and try process. The pipe OD is perfect but the pipe ID is a little too large, slit the pipe with a cutoff wheel until the pipe can squeeze tightly onto the ball studs leaving the slit slightly open.
    Do a last trial fit to check clutch fork positioning and braze the long ball stud together.

    The shortest length I could make was 1.75" (about 43mm) It worked adaquately with a short throwout bearing but slightly longer would be even better. The older fine thread ball studs are commonly short, the newer coarse thread ones are longer but shorter than mine.
  24. I have not done it . But as the Mercruiser is not particularly economical of fuel (15+ mpg) I'd get a torque converter that will lock out .
    You will probably adapt a Ford flex plate to a GM torque converter which must be exactly centered.
    With luck, the torque converter may nest into the end of an unmodified stock crankshaft

    Get a full set of junk parts and see what can be made to fit.

    In my 1800 lb car, once in motion, I don't shift much because of the abundant engine torque.
  25. tjm73
    Joined: Feb 17, 2006
    Posts: 3,380


    I didn't catch what you were asking totally in this post. The angled bell housing was used with the T5 transmission, not the Saginaw. They, as you know are top/tail shifters.
  26. tjm73
    Joined: Feb 17, 2006
    Posts: 3,380


    I've been kicking this idea around some more. And I am pretty sure this bell housing info is the Rosetta Stone of getting a Ford T5 onto the Mercruiser without special block machining. Just an after market T5 case and a small spacer. Relatively cheap too. It's late tonight, but I think I might try to go through the thread and put together a list of what I think will be needed to mate a Ford based T5 to the 3.7 with a GM bell housing and a mix of GM and Ford clutch parts without machining sometime in the next few days. A real hodgepodge of fun.
  27. Saginaws are cheap, abundant, reasonably durable and it appears that they would bolt on. But they would dribble oil at that angle and are therefore excluded. (an observation not a question)

    What does a T5 cost at swapmeets?

    If the bellhousings have the same length (they look as if they do), then the input shaft of GMC T5 may have a length compatible with a 5/8" shorter block and they appear to be an alternative to a Saginaw transmission (even on older bellhousings) on heavy cars. I replaced a 3 speed with a 5 speed transmission in my 2800 lb Mustang and found that I prefered the original 3 speed because the extra two speeds added little. Its v8 had a broad power band and the car was not heavy.
    Last edited: Oct 30, 2019
  28. advice for the novice:

    When attaching a manual transmission to its bellhousing, special care must be taken not to break the Saginaw transmission's thin, fragile cast iron bearing retainer.

    There are procedures to make it easier:
    1. It is easier to do this with the engine out of the car as the transmission is heavy and must be precisely positioned within a few thousandths of an inch.
    2. Place the engine on a dolly so it is easy to move side to side etc.
    3. Suspend the transmission from a comealong so it is easy to tilt and move up and down etc. This is your last chance to oil the end of the transmission shaft.
    4. bring the transmission and bellhousing together at the same height and insert the
    transmission's input shaft through the splines in the clutch disk. You will have to twist the output shaft, with the transmission in gear, to get the input splines through the clutch disk.
    5. it takes some effort to move the transmission forward into place. I use a ratchet strap for this. The input shaft must now be fitted into the crankshaft pilot bushing (or bearing). Jiggle it around until it goes in.
    6. the final thing to get together is the outer circumference of the bearing retainer and its matching hole in the bellhousing. more and more jiggling.
    Lifting the front of the transmission slightly with a small jack may help.

    7. DO NOT PULL THE TRANSMISSION INTO THE BELL HOUSING WITH BOLTS. THIS WILL GET THEM TOGETHER BUT WILL EASILY BREAK THE "SNOUT" OFF OF THE BEARING RETAINER IF THERE IS ANY MISALIGNMENT AT ALL. You can take up slack (evenly) in the bolts as the bearing retainer engages its nest and torque to 50 ft lbs.

    bullet ended assembly studs can help hold the transmission up and begin its alignment while attaching it to the bellhousing.

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