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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. CNC-Dude
    Joined: Nov 23, 2007
    Posts: 887


    It's a lot to read thru, but a similar but better remedy was discussed back on page 61.
  2. randydupree
    Joined: May 19, 2005
    Posts: 649

    from archer fl

    Where i had head gasket problems was where the lifter area and the water jacket dividing wall is,the wall is very narrow and i would get water in the oil when the gasket over the wall leaked.
    Using Mercrusier gaskets fixed that problem,the gasket has a bead of sealer where the gasket would touch the wall.
  3. distributorguy
    Joined: Feb 15, 2013
    Posts: 31

    from MN

    I've been lurking on this thread for a LONG time, and the biggest question I have has now been answered:
    What was the factory timing curve in the distributor??? Look to the source of detonation if you have a detonation problem: increased heat from improper spark timing. The factory distributor, while a decent unit, is set up all wrong.

    I just mapped out the existing timing curve as 32 (crank) degrees of mechanical advance starting just above idle speed to all-in at 3000 rpm. Add a few more degrees for a loose timing chain, then add your base timing setting onto that as well. A simple distributor recurve is in my future, plus an alloy head, 12 lbs of hard block filler, zero decked block, 1.8 roller rockers, and a stock cam. Likely the 2 bbl FiTech system to boot - all stuffed into a 1964 Land Rover Series 2A.

    Randy, how is the Mercruiser gasket identifiable? Black with red O-ringed beads? MLS? What's so special with it? Why not use a Cometic head gasket? I just peeled a failed FelPro out of my motor from the P.O.
  4. tjm73
    Joined: Feb 17, 2006
    Posts: 3,372


    I've been thinking about a T5 to 3.7 Mercruiser adaptation. I read a few earlier posts that I had missed that sent me off on a research task.

    All the info I have found implies the Jeep Iron Duke T5 had an input length that is almost identical to the Ford Foxbody Mustang T5. The difference being just 0.008"-ish. So we can call them the same. As a result the bellhousing is the correct depth for a Ford T5 on a 3.7 that has been cut back 5/8". But what if it hasn't been cut or a guy doesn't want to have it cut? Well, I think Ford has you covered. In '94 Ford went from a 7.189" input to a 7.870" input. That's an increase of 0.681". Now if you didn't cut the 3.7 block you have an input that is just 0.056" too long. Not even 1/16". Is that tolerance too much? I don't know. If the clutch moves on the splines enough, but the snout prevents the seating of the trans/bell, it seems a cut off wheel would solve the issue.

    Thoughts on above?

    Also here's a little info on the longer input T5's. The V8 and V6 boxes were a little bit different. What's the same? Input length, diameter (1- 1/16", 10 spline), reverse gear ratio (3.15) and pilot bushing diameter (0.668"). Also they use the same shifter. What's different? The torque rating is different. 300 lb-ft for the V8 and 265 for the V6 box. Ratios are slightly different too with 3.35/1.99/1.33/1.00/0.68 for the V8 vs. 3.35/1.93/1.29/1.00/0.73 for the V6. Lastly the speedometer drive gears are different with the V8 having an 8T and the V6 having a 7T.

    Either would be suitable IMO. In fact, the V6 cars were 3.8's with 145-200ish hp. which is right in the range of the 3.7 Merc. And the V6 was not exactly a revers. Early (lower power) cars were done by about 4000rpm and the higher power cars were done around 5000 rpm.
    Last edited: Apr 13, 2019
  5. tjm73
    Joined: Feb 17, 2006
    Posts: 3,372


    Further research has yielded a possibly better all bolt up no machining needed option.

    The standard GM Muncie/Saginaw bellhousing depth is spec'd at 6.29" with a 4.6875" retainer hole. The transmission that bolts to this bell has a 6.5" input shaft length, leaving 0.21" of the shaft to interface with the pilot bearing.

    Hot Rod Works sells an adapter to put a Ford Foxbody Mustang spec T5, with it's 7.18" input shaft length, on the common GM M/S bellhousing. To maintain the 0.21" input to pilot bearing dimension the adapter must be 0.68" in thickness.

    On the 3.7 Mercrusier with out it's bellhousing area cut down there is 0.625" of additional bellhousing mount depth. If you add that with the 6.29" GM M/S bellhousing depth and the 0.68" adapter depth you get a total effective bellhousing depth of 7.595".

    In 1994 Ford increased the T5 input length to 7.84" for both V6 and V8 Mustangs. If you take that and remove the effective bellhousing depth of 7.595" you get 0.245" of input to interface with the pilot bearing. Just 0.035" longer than the stock GM spec.

    The GM bearing retainer hole is 4.6875" and the Ford bearing retainer is 4.91". You can chuck the Ford T5 retainer up in a lathe and turn it down a bit and that problem is solved.
  6. BigBlock6
    Joined: Jul 6, 2015
    Posts: 4


    Where are you at with these cam coes?
  7. Thanks Randy....The most recent Mercruiser gasket that I bought has no sealant beads on it and costs much less, Without the beads I question its worth. Felpro does have sealant beads so that may be the way to go. I have not had coolant in my oil yet, but I did experience catastrophic hydrolocking. I do not know what fluid was responsible.
    I did not have a replacement 3.7 so I temporarily used a merc 120 ...its power is disappointing (feels like about half of that of the larger engine). It is due for replacement now that I two more 3.7 's. I put an updraft carb on the 120 and it works well.
  8. Shops are complaining that they lose money cutting blocks down for me.
  9. tjm73
    Joined: Feb 17, 2006
    Posts: 3,372


    I think I figured out an ever simpler way yet if you are ok with running, or want to run, a T5. First off, this idea pivots on either running a GM Muncie style T5 World Class main case (kinda hard to find I have read) or buying an aftermarket main case from G-Force transmissions. The G-Force case is stronger than stock and is a "tri-fit" (EDIT: it's not. See note at end of post). It fits GM Muncie, Ford T5 and Ford Top Loader mounting patterns. The cost for them is almost the same, so searching for a GM case may be a waste of time unless you can score a GM WC/T5 cheap enough.

    So once you have the main case you have to assemble the Ford World Class T5 "guts" into the GM Muncie World Class main case (or the G-Force case). This gives you two things you want. The GM Muncie pattern fitment and the Mustang's 7.18" input length. It also gives you a chance to rebuild the T5 to factory fresh condition.

    Next, you need any run of the mill GM bell housing that is 6.3" deep. New or used, doesn't matter. Just use the small register bearing retainer hole bell housing, not the larger truck version. These small retainer bells are super common and cheap. They even repop them. Summit sells a repop for $230. But, GM aluminum bells can be even cheaper. Some guys might even have one laying around.

    Next, you will need to take the Ford bearing retainer and turn it down to the GM diameter. And install it on the transmission. For reference that's turn it down to 4.6875". You may be able to just bolt a S10 T5 bearing retainer on. In fact I am pretty sure you can, but the length may need to be checked.

    Next, you will need to make a simple 0.080" (readily available 5/64") aluminum spacer to mount between the block and the GM bell housing.

    Last-ish, you will need to have the crank machined to accept the Ford spec pilot bushing. The FRPP M-7600-A is a needle bearing unit that is pretty cheap. Around $15 bucks. And it's the match to the Ford T5.

    When you assemble this, you should be pretty close to one the money ready to go. It's uncut block/spacer/GM bell/T5.

    You can also run a close ratio gear set that's available and a Ford specific forward shifter mount tail case.


    So reading more into the G-Force case, I found out the case is NOT "tri-fit" but in fact one case is made for the two Ford patterns and one is made for GM. Both are for World Class "guts" so the rest of the info should still be valid.
    Last edited: Dec 1, 2019
  10. Stock small block chevy aluminum bell housings sell for for $20 each. Saginaw transmissions go for $65. You can always find either at inflated prices.
  11. A cheaper alternative to milling the bell housing end of the block might be making the cut yourself with an abrasive cut off wheel mounted in a angle grinder or a router. The angle grinder or router would have to be mounted firmly on the top side of an aluminum plate that is free to slide around on the rear surface of the engine.
    As the abrasive wheel is smooth in its operation, the cutting would not have the violence of a milling cutter not securely fastened. A special arbor would have to be made for the router if that was your choice. An angle grinder would be an easier choice as long as it can be set up for the needed cut depth.
    Dished cutting wheels and a thinner plate may be needed to get the 5/8" cut.
    I intend to try this method in the near future.
  12. I measured my 4 1/2" Hitachi angle grinder and there is little over 3/4" to work with so it should remove 5/8" as a non-adjustable tool (easier to make and less to go wrong in using it).
  13. Three Widow's Garage
    Joined: Jan 18, 2010
    Posts: 206

    Three Widow's Garage

    I'm planning on the same tactic, only leaving the crank and flywheel in place. Use a cutoff wheel or sawzall to remove the majority of the material, then mount a router to the edge of the flywheel and rotate the crank to clean up the last bit of material. Carbide router bit or 1/2" end mill should work with a little oil. The router would have to be stepped over to get all areas. I'll post it up when I get some time to do it.
  14. advice to anyone new to Mercruiser engines:
    Considering the scope of this thread it is easy to miss things, so in case there is someone out there contemplating a Mercruiser 4 cylinder aluminum Mercruiser engine, here are things I learned from mistakes:
    1. the basic engine is very good. It is very light and has the power and torque of a small block ford v8. In a light car there is enough torque that a 3 speed transmission is fully adequate.

    it has weaknesses in its alternator( low output and its magnets fall out) , voltage regulator(expensive and fails if water is not flowing through it). Headgasket leaks are common problems and coolant can leak into its oil from the waterpump.

    to solve the above: use a belt driven Toyota waterpump and any small automotive alternator. I have used Mercruiser headgaskets but I do not know how good the new ones are.

    The cylinder walls are thin so if the engine bore is already .030 oversize and needs reboring I'd be cautious. .040 pistons are cheap and common, so are .030 pistons. .015 or .020 is a better rebore size if you can find the pistons and rings.
    For the foregoing reason, I try not to buy engines that have been rebored, (the block is stamped indicating this) Boat repair shops commonly do not repair this engine so you may have your choice of them in boatyard scrap piles for $100. If you find a really good engine for $1000 it is cheaper than rebuilding an engine.

    Although it is a light engine, it has a heavy starter and a heavy head...they can be replaced with much lighter parts roughly $100 for a geared starter and much more than that for an aluminum head.
    You could also replace the battery with a lighter alternative like supercapacitors and save a lot of weight. They discharge easily so it would be viable only if the engine started very easily.

    Once the rear of the block is shortened 5/8" a small block chevy bellhousing will bolt to the block ( avoid the larger hole truck bell housings that couple to useless ratio truck transmissions) a Saginaw or Muncie transmission will bolt on to the bell housing.

    The engines I have come with Ford flywheels, just scrape off the paint and bolt a mid 80's Mustang pressure plate to it. Use a chevy clutch disk to couple to the chevy transmission.

    Stock, these engines tend to run hot and knock. One solution is to lower its compression ratio with dished pistons.

    Mercruiser's chose to retard the ignition timing so it did not knock but this made their engines run hot. They would have been better off to change the camshaft.

    Or you could run it on race gas or E85.

    Another approach is to cut the top of the block flush with the pistons tops. ( although the compression ratio would be higher , the violent turbulence which results reduces knocking). There are camshaft profiles for this engine that don't knock , mine didn't.
    Last edited: Oct 10, 2019
    kidcampbell71 likes this.
  15. Compression ratio, valve timing and throttle opening interact to control cylinder pressure and knocking. Charge stratification, ignition timing and fuel octane rating also enter in. Mercruiser chose to retard ignition timing when fuel octane rating became lower. This reduces power and the engine runs hotter. (bigchief wrote this at the beginning of this thead).

    At a cranking compression of 165 psi my engine had no knocking problems. Its cam wore a little so I replaced it with an Elgin cam. Cranking pressure increased to 211psi and the engine now had spark rattle (knocked) even with its throttle closed until ignition timing was retarded to fire at 28 degrees. The engine then had a very high exhaust gas temperature (1740 degrees). The new Elgin cam was useful only as a core for regrinding.
    Last edited: Oct 13, 2019
  16. There are differences in small block chevy bell housings. The Ford flywheel used by Mercruiser is larger in diameter and causes fit problems with car small block bell housings. The pickup bellhousing fits fine but swap out the smaller diecast bearing retainer for car transmissions for the larger pickup bearing retainer and all is well. Don't buy the useless pickup transmission unless you can't find a bearing retainer. Be very careful aligning and bolting the transmission to the bellhousing as it is really easy to break the bearing retainer unless the transmission input shaft plugs into the pilot bearing in the crankshaft. Miss the hole and you are in trouble... big transmission shops should have the bearing retainer.
    Last edited: Oct 12, 2019
    kidcampbell71 likes this.
  17. If you need the larger bellhousing, it is easy to identify as its angular deeper bottom is shaped like a tin can while the smaller one is tapered at its bottom and the center hole to fit the transmission is larger on the pickup bellhousing.
    Last edited: Oct 12, 2019
  18. chev truck bellhousing.jpg bellhousings car and pickup.jpg
    This is for anyone new to the difference in chevrolet car and pickup bellhousings the photos are not mine I'm using the unpainted style above with 5 bolts to the transmission. For comparison the center holes in the unpainted bell housing and the black one are the same diameter
    Last edited: Oct 18, 2019
    kidcampbell71 likes this.
  19. GearheadsQCE
    Joined: Mar 23, 2011
    Posts: 2,498



    Thanx for keeping this thread alive. I'm still trying to buy some pieces to do a mock up. I think I have some stuff figured out that might be new to this thread. But, I want to be sure it works before posting.
    kidcampbell71 likes this.
  20. A manual transmission depends on moving the pressure plate, the choice is between moving it directly with hydraulics or with a clutch fork. The hydraulic release bearing system is nice except its adjustment with shim washers will require several trial assemblies of the transmission to the engine to check clearance. It is really easy to break the bearing retainer doing this so you may want a spare bearing retainer on hand. Don't pull it together with the transmission attach bolts or I promise the bearing retainer will break like mine did years ago.

    Push rods were the usual stock solution, but there are things which can go badly wrong with them when you make your own (as I found out).

    External clutch slave cylinders are another choice but they have most of the disadvantages of their alternatives and offer few advantages.

    If everything fits well, a good simple system is a cable pulling on the clutch fork . I use an old parking brake cable to pull the clutch fork . It works reliably and is really cheap. I extended the clutch fork on a previous engine a few inches for more leverage. Reshaping the clutch fork may result in the throwout bearing to clutch fork angular limit being exceeded.

    You must have a clutch fork that does not begin at the end of its travel in the bellhousing opening for it. Resist cutting the bellhousing as there is not much to gain by doing that. Although the choice of Chevrolet clutch forks is wide (see photo), you may have to cut and weld what you have to the shape and length you need. Heating it may cause the metal to become softer and it may not resist bending( that happened to my Goldwing centerstand).
    . clutch forks assorted.JPG
    stores here stock one clutch fork an ATP ZA 100 or a Pioneer CF 100 which look like a mid 70's Chevy fork the 340278 (Chevy part number). In striking contrast, you can see in the above photo how many Chevy clutch forks were made.

    You can change the clutch fork to clutch disk to throwout bearing distance minus 650 thousandths using the long throwout bearing. Another minus 650 thousandths by using a V8 style pressure plate with inclined fingers instead of the 6 cylinder one with flat fingers. The converse applies: 650 th more clearance with the short v8 throwout bearing and another 650 th clearance increase with the 6 cyl style flat fingered pressure plate.
    Other than the above, if it needs adjusting, make a new fork pivot ball stud. Mine is refusing to unscrew in spite of penetrating oil and a long breaker bar.

    While you have it apart change the shaft seal in the transmission bearing retainer. The original seal is a # 125172C mine now is a new Duro #D431.
    Last edited: Oct 29, 2019
    kidcampbell71 likes this.
  21. I once tried using an end mill in a drill press, intending to feed the aluminum in by hand. As soon as it contacted, the cutting became so violent that I immediately gave up the idea. Your idea has its merits but you need to feed the cutter slowly with a screw advance unless you use an abrasive wheel. Your method would need crankshaft endplay limited to nearly zero while cutting.
  22. I'd like to hear about it. Don't be afraid about it not working, present it as theoretical don't wait for perfection. I have found innumerable ways for even simple ideas not to work. The old saying is " If you are not making mistakes, you are not trying hard enough(not innovating)".
  23. 2019 prices :
    I found that hydraulic(slave cylinder) throwout bearings are as cheap as $66 That is $10 less than the only throwout bearing at the closest NAPA store. add a $20 clutch fork and $76 ( I told him that $76 was insane, triple what Summit asked) becomes $96. (Summit has throwout bearings start around $25+ postage). I bought mine locally a few years ago for about $15.
    (I'd not get the cheapest when a chevy one is $100)
    With luck, you may find a hydraulic clutch pedal and master assembly in your wrecking yard.
    It will help to use the slave and master cylinders from the same car so you have usable leverage over the clutch springs. (3/4" bore is commonly called for on the clutch master cyliinder).

    With a cable setup, changing leverage is as easy as drilling cable attach holes in a better place.
    Last edited: Oct 16, 2019
    kidcampbell71 likes this.
  24. TCATTC
    Joined: Oct 12, 2019
    Posts: 11


    I have lots of 3.7 parts and a couple core engines if anybody is interested
    kidcampbell71 likes this.
  25. lengthening throwout bearings instead of lengthening the pivot ball stud

    Throwout bearings are traditionally made mainly of machined cast iron.
    Chinese throwout bearings #614037 are assemblies of stamped steel, a cheaper method.
    Steel is better for welding an extension onto if you can't lengthen the ball stud when things don't fit.

    throwout bearing  special long.jpg

    this bearing is a special long one (mostly cast iron) that fits pinto transmissions. Probably not of use to us but it is shown here as an example of what can be found. price is double that of a cheap throwout bearing. Dimensions were not given.
    Last edited: Oct 16, 2019
  26. Make certain your flywheel will fit inside the car bellhousing. Mine did not so I had to use the truck bellhousing. If you fit a smaller diameter flywheel the starter is unlikely to engage it.
    Last edited: Oct 16, 2019
  27. tjm73
    Joined: Feb 17, 2006
    Posts: 3,372


    Isn't the flywheel contained with in the "shroud" of the 3.7 block? I'd have to go dig through the thread but I think the correct size flywheel is mentioned.
  28. I think I have 2 maybe 3 of these machined and ready to assemble from a hoard I bought. Gonna try and assemble them this winter. Just chiming in so I can find this thread again.

    Sent from my SM-G965U using The H.A.M.B. mobile app
    kidcampbell71 likes this.
  29. I use the flywheels which come on the 3.7 engine, with a flywheel diameter change, the starter gear teeth would no longer engage.
    On the 3.7 engine that I have open the flywheel runs back within the bell housing. The fit problem is in the edge of the bell housing near where the chevy starter fits. The bellhousing is shaped inward just at this place. The flywheel interferes with the smaller chevy bellhousings at that point but the larger truck bellhousing went on easily. The orange bellhousing (post 2028) has much less room inside than the larger black one (post 2028).

    I have another newer car bellhousing that goes over the flywheel is the odd one that runs the transmission tilted over to the left
    [edited after looking at some bellhousings]
    Last edited: Oct 18, 2019
  30. bellhousing 001.jpg
    two car bellhousings. the left one is much newer, notice that there is a bracket for a slave cylinder on it and notice the angle the transmission would run at. Its clutch fork is beside it. It is not curved and its pivot point is much farther from the center hole. The other bell housing is the bellhousing which unmodified will not fit Mercruiser 3.7 engines.

    bellhousing 002.jpg
    this shows the general area which needs to be removed to make room for the flywheel in the old standard car bellhousing. Mine is not finished but so far it is about 12" long and needs to be larger along its circumference. You will need to measure and mark the exact area to be removed. It would be bad to have gravel get stuck between the flywheel and the bellhousing so make a cover for it.

    bellhousing 003.jpg

    It took a deep cut across nearly the full width of this bellhousing. The opening for a clutch fork limits how far the metal removal can go. Aluminum fatigues easily so round the corners smoothly and sand it to remove stress risers and keep the holes small if possible. It will last much longer then.
    [this is a car bellhousing (3858403) not the black truck bellhousing shown earlier.]
    Last edited: Oct 29, 2019
    kidcampbell71 likes this.

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