Register now to get rid of these ads!

The elusive 224/3.7 MerCruiser banger

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

  1. Flatrod17
    Joined: Apr 25, 2017
    Posts: 150

    Flatrod17
    Member

    Dennis,
    Are yours adjustable? If so try turning them down another 1/4 to 1/2 turn. if not adjustable , you will need to take a little off the bottom of the fulcrum. That is if its not some other problem with oil pressure.
     
  2. They are not adjustable and you have the right solution. I forgot that I had shimmed that one rocker up. Measured the gap at the valve stem, it was 85 thousandths. Removed the loud rocker for inspection, found and removed 85 thousandths in shims(two shims). No more knocking. I appreciate your interest, willingness to help and good suggestions.
     
  3. GearheadsQCE
    Joined: Mar 23, 2011
    Posts: 2,803

    GearheadsQCE
    Alliance Vendor

    Concerning Beck's cam situation:
    A shorter connecting rod is not the answer. That would have the same effect as thicker head gaskets, less quench, more prone to detonation.
    From what I have read, dynamic compression for E85 should be right around 10:1
    Using your cam information, I calculate that is almost exactly what you have now.
    Retarding the cam 4 degrees will drop the dynamic compression about 1/2 point.(9.5:1)
    Cutting 10cc from the dome will bring it down to 8.9:1

    My gut tells me that the better solution is to have the cam ground on a tighter lobe centerline. 108 degrees would give you 10.4:1 dynamic compression using your current lobe profiles. This generally gives more mid range torque.
    The problem then is to get the cam ground and that might not be possible on a regrind.
     
  4. beck
    Joined: Sep 20, 2008
    Posts: 262

    beck
    Member

    I understand the 13.6:1 that I quoted was static compression
    I have no idea how dynamic compression is calculated, nor a reference in my mind what is high or low. I do understand that dynamic compression is when the engine is running.
    Wouldn't a cam with a 108 degree centerline close the valves even sooner?

    Will setting my current cam to 113 cost me torque, HP, or both?
     
  5. GearheadsQCE
    Joined: Mar 23, 2011
    Posts: 2,803

    GearheadsQCE
    Alliance Vendor

    Yes, closing the centerline will close the intake sooner (all else being equal). But it also causes greater overlap. With the intake and exhaust being open together, longer, some of the cranking compression is bled off.

    Generally, retarding the cam will shift the torque up the rpm scale. This doesn't have much effect on the actual number. Since horsepower is a function of torque and RPM, you may gain some hp.

    As you said earlier, once you've gotten the engine torn down far enough to change the cam timing, you are almost far enough to just go ahead and replace the cam. But, it might lower the cranking compression enough to get it started. It may be worth a try.

    Do you have a way to measure cranking RPM?
    Also, Flatrod17's suggestion of getting the engine spinning before introducing the fuel and spark is a good one. The sprint car guys have been doing that forever.

    Edit:
    Retarding the cam causes the intake to close later, which means that the piston to valve clearance is less. You can check that without removing the head by using a light valve spring and a dial indicator on the retainer. With a degree wheel installed, you just rotate the engine a couple degrees at a time and press the rocker arm until the valve touches the piston. (the closest point will not be @ TDC) The indicator will give you the V/P clearance.
     
    Last edited: Sep 26, 2021
  6. Flatrod17
    Joined: Apr 25, 2017
    Posts: 150

    Flatrod17
    Member

    I always get confused with all the cam talk. Intake center line and lobe separation get thrown out at the same time and then I get confused. I always thought advancing the cam promoted torque, retarding promoted horsepower. When I built our small block drag race engines I always installed the cam by cranking compression. (it had the kind of cranking compression that Beck has) Generally that was always 4 degrees advanced from the recommended intake lobe center line, to get the most cranking compression (which was about 20 pounds more) which gave us the most torque on the dyno.

    I will add that QCE checking V/P clearance is a good way to check. It is done at TDC on the over lap, when both valves are open at the same time.
     
  7. beck
    Joined: Sep 20, 2008
    Posts: 262

    beck
    Member

    I was trying to reset the cam to 113 degrees but overshot to 118 degrees. I knew it was too far but decided to test cranking compression there. It still made 250 psi. when cranking with the throttle blade open. Something is definitely not right. I am afraid there is something I am doing wrong or missing. Before I tear the motor completely down for piston dome reduction I am going to take it to an engine shop to have them degree the cam. Hopefully they will allow me to watch and learn. It may be many weeks before that happens (5 days a week physical therapy), so updates may take quite some time.
     
  8. beck
    Joined: Sep 20, 2008
    Posts: 262

    beck
    Member

    I believe I found the cause of the high cranking cylinder pressure. Sometimes we ask ourselves, “Why didn’t I see that before?” I was pulling the motor apart to cut the piston tops. I noticed the pistons sticking out of the bore. I didn’t do any fancy measurement, but using a feeler gauge it looks like there is a .015 stick out. Either the deck height was measured wrong or the custom pistons were made too tall. My 13.6 :1 compression ratio was calculated with piston flush to the deck. Now I believe my easiest solution is a thicker head gasket. Since there was minimal piston to head clearance, I’m hoping I won’t kill the quench and cause detonation.

    I am going to try a MLS head gasket. The company I ordered from had one listed for our motors, but only in .040 thickness. (The Mercruiser gasket is about .050” thick) I ask about their BBF gasket and they said the stamping was identical to the Mercruiser. It was available in various thicknesses. I ordered a .080”. This will give me about .015" more than what I originally planned for, giving me about 12.9:1 compression.

    Gasket dealers have been reporting up to a 6 month wait for their orders to arrive. I called direct to the MFG. I was told those were stocking orders and mine should ship in 3 weeks. I did however have to pay the full list price which was much more than their dealers charge. Now I wait for the part to arrive.
     
  9. It is common to need to replace headgaskets on our engines, so when you find something that works for you, buy a spare. An .080 gasket has twice the area for compression pressure to work against than a .040 gasket does. So the thick gasket has less resistance to a given amount of pressure than a thinner gasket. Pressures that would be a problem for a composition gasket may not be a problem for the stronger mls gasket.
     
  10. Flatrod17
    Joined: Apr 25, 2017
    Posts: 150

    Flatrod17
    Member

    Beck,
    I thought there was something not right with your engine. Hopefully you found it! As for the quench not being right, I have run a BBF marine engine with the pistons .055 down the bore and had no signs of detonation. It did require a total of 55 degrees of timing to run the best on the dyno. I think if you can keep the quench between .040 and .065 you should be good with no signs of detonation. If I read your numbers right you should have the .065.
     
  11. Flatrod, were you using flat top pistons and a Ford wedge head? I did with 35 thousandths quench under the flat part of the combustion chamber, I suppose it had good swirl. It had no detonation (until I changed to an Elgin camshaft, and then all it did was detonate.)
    Beck has his combustion chambers mostly filled in with piston crown.
     
  12. Flatrod17
    Joined: Apr 25, 2017
    Posts: 150

    Flatrod17
    Member

    Yes it was a flat top piston, wedge head. Small chamber heads, I don't remember the size, but it had 10 to 1 compression. Quench would of been around .095. .035 is pushing it, any smaller and air tends to get stuck over there and it will detonate.
     
  13. Yes, it was a zero decked engine all that averted pistons hitting its head was the headgasket's thickness .035". I sold my old truck last spring it was a 1954 chevy 6700 with a tag axle added. It had power steering, a 2 speed axle, a Browning and the regular 4 speed. It was competitive in farmer's cherry truck races as its engine was new.
     
  14. beck
    Joined: Sep 20, 2008
    Posts: 262

    beck
    Member

    Our motors have a mix of other manufactures parts in use. Does anyone know what the oil relief valve in the oil filter housing is from? I had been priming my motor with a long hex shaft and my cordless drill. There must have been enough pressure to open the relief valve. When the pressure dropped the disc that closes it wedged in it at an angle letting it open.
    oil bypass valve small.jpg

    I suspect I had debris stuck behind this relief valve when my motor was assembled. I had glass bead blasted the block to remove the factory paint. I thought I had it flushed well, but just found bearing damage. My motor has never been started, but has been rotated considerably with the starter. I have been fighting a high cranking pressure issue. When I took the motor apart to trim some from the piston domes I found rod journals scuffed and bearings worn. The main journals aren’t shiny any more, but the bearings don’t look bad. I have taken the crank to the machine shop to see if it polishes out without having to turn it further.

    My memory is failing me. I don’t think I had removed the relief valve. Looking at it I don’t know the best way to remove it without destroying it. I am picturing a half circle that will fit inside the valve where the disc seats. That half circle would be attached to a small slide hammer? Or possibly a pair of ears that pivot to make an inside puller?

    I can’t quite figure out the use of this relief valve. From its location it appears to be a filter bypass, but isn’t there one built into the filters?

    ---UPDATE-- My relief valve was easily removed with a little prying with a small screwdriver. It came out easily enough that I may have done this the 1st time through and just don't remember it. I found no dirt.

    I have been told, but not confirmed, that this relief valve is the same as the L6 Chevy 6 cylinder and the MK V and MK VI big block Chevys.

    Some high performance builders choose to plug the hole this relief valve is in. Again not confirmed, the hole appears to be the correct size to run a 1/2 NPT tap into and is plenty deep for the plug. The hole is close to 18mm which they make an oil galley plug to fit.
    EDIT AGAIN-----Scratch that 18mm galley plug. It doesn't fit.

    I have again scrubbed my motor using brushes in the oil passages. After drying I will put the galley plugs back in and continue assembly as parts are cleaned and checked out.
     
    Last edited: Oct 21, 2021
  15. Flatrod17
    Joined: Apr 25, 2017
    Posts: 150

    Flatrod17
    Member

    Beck, I would leave it in place, it is a filter bypass as you thought it is. You can get new ones from Pioneer part number PG280 or PG580.
     

    Attached Files:

  16. beck
    Joined: Sep 20, 2008
    Posts: 262

    beck
    Member

    My local parts house had to UPS ship the Pioneer one in, so I passed. I found a GM one with 30# relief rating. The higher pressure rating was recommended by another builder. It kind of splits the difference between plugged and stock. GM part # 25161284. Blowing up an oil filter didn't sound like a good time. This one should still protect against that. I ordered from Amazon. With tax it was $13.38.

    My head gasket is supposed to be here tomorrow, that's about 5 days ahead of schedule. Naturally I have the whole motor disassembled now.
     
  17. GearheadsQCE
    Joined: Mar 23, 2011
    Posts: 2,803

    GearheadsQCE
    Alliance Vendor

    Beck,
    Sounds like a good compromise.
    Just curious, What kind of oil pressure were you seeing while cranking?
     
  18. beck
    Joined: Sep 20, 2008
    Posts: 262

    beck
    Member

    Sorry, it has been over a month ago when I did that so I don't recall the oil pressure. I do recall that there was pressure.

    I had the bottom end of the motor assembled at a performance shop last time. I was going to do it myself this time. When I started balancing the pistons I found one wrist pin 4g light. Closer inspection showed that the ID was larger. I wonder how that performance shop balanced it? I haven't checked the rods yet. Possibly they took material off the top end of 3 rods? Sometimes you don't get what you pay for. I had purchased the pistons and wrist pins through them.
     
  19. Flatrod17
    Joined: Apr 25, 2017
    Posts: 150

    Flatrod17
    Member

    A lot of shops assume custom pistons all weigh the same and just use one for a weight. Also a 4 cyl does not need a bob weight. I always jokey the pins to find the best weight on the set. If you have to take the weight off the piston to make them the same 4 grams is a lot. You can run it as is, as you will never feel that 4 grams, and if it was needed to make a bob weight 4 grams would only make about a 2 gram difference on the crank. Again lots of shops use one rod for weight too. If the rods have been balanced properly, one rod (or more) will not have any marks where weight was removed, both little end and big end. As a comparison my pistons with pins weigh 759.5 and my aluminum rods weigh 481.5 rotating end and 198.5 reciprocating.
     
  20. Flatrod17
    Joined: Apr 25, 2017
    Posts: 150

    Flatrod17
    Member

    As far as putting it together yourself, all the hard work should of been done with all the clearances. You should have no problems there. If you do put different bearings in, make sure the upper and lower are the same size as what you took out. A lot of times we will use std on one side and a .001 under on the other side to get the clearances we need. That's where the need for Cleveland bearings comes in, you can get them in .009 and .011 if you have a .010 under crank so you can custom fit for the bearing clearance you want/need.
     
  21. beck
    Joined: Sep 20, 2008
    Posts: 262

    beck
    Member

    Originally I thought the mismatched wrist pin came from the piston mfg. I no longer believe that. There is slight running wear on the mismatched one. The other 3 are mirror shiny yet. I now think the shop that assembled the bottom end must have had another set laying around and mistakenly stuck it in. I have emailed the piston mfg trying to purchase 1 matching or a set of 4 wrist pins.

    My crank is .020" under.
     
  22. Flatrod17
    Joined: Apr 25, 2017
    Posts: 150

    Flatrod17
    Member

    And while we are here on oiling, what is everyone doing for oil pans? I didn't like the stock pan, can't afford a alum pan, so I made a box pan out of mine. Now to add trap doors and a windage tray. pan.jpg pan2.jpg
     
  23. Flatrod17
    Joined: Apr 25, 2017
    Posts: 150

    Flatrod17
    Member

    Possible King might make bearing at .019 and .021 for the Cleveland other wise have to get clearances by grinding/polishing the crank to get what you need. When they assembled your engine, did they give you a build sheet with what everything is?
     
  24. the odd wristpin may have been swapped into your set to balance a light piston. There comes a point when shortening the wristpin for balance purposes may not be enough. It is all different now that you gave your pistons a "haircut" so the balance should .be redone for each of the pistons, connecting rods(both ends) and wristpins.
     
    Last edited: Oct 24, 2021
  25. GearheadsQCE
    Joined: Mar 23, 2011
    Posts: 2,803

    GearheadsQCE
    Alliance Vendor

    My guess is that the original builder either lost or damaged one of your pins. I have never had a set of pins that needed to be altered for balance. You can't get 4 grams out of a piston (at least not one that you would be using in a build of this quality) They should be buying you a new pin or a new set.

    As Flatrod17 said, balancing a crank for an inline engine doesn't require a bob weight. So, as long as the big and little ends of the rods match, and the pistons weigh the same as each other you should be good to go.
     
  26. I prefer to balance individual components but was suprised to see it done to balance pistons. His assumption must have been that the piston wristpin and rod would be a permanent assembly. This seems an unreasonable assumption. However, steel being denser requires less metal removed. Yes, in a set, wrist pins are very very close in weight but still, I assume nothing and carefully weigh the reciprocating parts.
     
  27. Taking more oil may be an advantage. Is that why you did it? Your pan looks really nice. I just use stock pans
     
  28. Flatrod17
    Joined: Apr 25, 2017
    Posts: 150

    Flatrod17
    Member

    Dennis G,
    Yes I wanted more oil in the pan. When I was working we seemed to always see the 3.7 Mercruiser's with burned up rods, may of been from the Marine use, or just nobody checked the oil. I will have baffles and trap doors when done. I like to go around corners a little to fast sometimes and I want to keep the oil at the pickup.
     
  29. drtrcrV-8
    Joined: Jan 6, 2013
    Posts: 1,497

    drtrcrV-8
    Member

    Flatrod17 : What do you figure the capacity of the new oilpan to be? or more properly : How much oil do you plan to run when you're done? I've never liked the "stock" pan either, so that's why I'm asking.
     

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2021 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.