Posted: Thu Sep 08, 2011 11:35 pm Post subject: Proper connecting rod orientation
This just came up on the sale board and I thought it would be very useful to bring it over here to the tech board.
While we are in the education mode I'll post an edited version of Skyjeep's open bottom end. Rods are different between 1 & 3 and 2 & 4. They have different part numbers because they must be installed with their narrow side towards the nearest crank counterweight and at the same time their oil squirt hole must face away from the cam. In addition when you assemble each piston to the rod you must make sure that piston's "T" slot will end up facing the cam. It can be tricky but any experienced engine builder can get it right.
It would be interesting to know the builder on these engines.
Joined: Aug 25, 2011 Posts: 10 Location: Apache Junction, AZ
Posted: Thu Sep 08, 2011 11:52 pm Post subject:
I had a machine shop press new pistons on the rods of my AMC 304, and one was backward. I was glad I checked! _________________ ? M170 52 M38 M416 M274
59 CJ6 85CJ8 68 Bronco 72 F100 4x4
00 Discovery II
Joined: May 14, 2009 Posts: 972 Location: South Dakota
Posted: Fri Sep 09, 2011 6:06 am Post subject:
If you don't do this correctly, you get 105 miles before you lose oil pressure. In the pan will be a nice pile of rod bearing material under each rod. The book said to put the offset away from the nearest main bearing. Confusion got the best of me and I did it 100 % wrong. 300.00 later, I figured it out. The machine shop owner said:" education is expensive". I believed him. No pain, no gain. I still go very slow when I get to this step. Nice illustration! John
Joined: Apr 08, 2009 Posts: 249 Location: Mariposa, Ca.
Posted: Sun Sep 11, 2011 9:25 am Post subject:
I'm curious if this is the same issue my builder brought up during the assembly of my engine. I have built engines before but not one of the Willys products. And it's been a few years. Okay, a lot of years. So I took the block in and had the engine done as a long block job.
When taking the engine apart, the shop owner said two of the rod bearing caps were turned around. I believe he said the middle two. He thought the engine had been assembled incorrectly last time around. When putting the engine together, he tried to orient the caps all the same direction and found the crank would not turn, or at least was too tight. So he put it back the way he found it. He did not mention this until I picked it up and THEN he asked if I had heard of this. He also thought that maybe the crank had been turned to fit this way.
I trust him that he knew what he was looking at when he took it apart but he obviously has no more experience with the military version of this engine than I do. He set the valves to the civilian spec even though I told him what I wanted. So I am wondering if this is a common thing to experience. I must admit that I have a little apprehension on what may happen when I hit the 103 miles on mine.
Joined: Feb 16, 2007 Posts: 206 Location: Gold Coast Australia
Posted: Sun Sep 11, 2011 12:08 pm Post subject:
I would not trust any of these guys especially those who have worked on too many V8's where oil squirt holes etc were placed differently.
I suggest you ask more questions or your rundown is not exactly what he said.
Rod caps are fitted together one way in the machining process & bored so as to have a perfectly round hole the bearings are tabbed into.
Then they are usually numbered as mating parts.
If the machinist indicated the caps had been reversed this would indicate the numbers would not be aligned & the hole would no longer be round as the 2 halves are no longer aligned, as they were in the original machining.
Usually putting caps on back to front will lockup the crankshaft.
What does not sound right is you indicate he said he had to put the caps back on the way they came off....which he earlier had told you was wrong way round.
Now a good engine machinist will always re-size con rods & check for & correct straightness/alignment.
Had this machinist done this there IS NO WAY those caps would need to go back on other than the correct way [the way they were mated when NEW].
Re-sizing re-establishes the PERFECT circle for the bearings to sit in, just as new.
I would be asking more questions & re-checking his work.
Establish for sure where the con rod oil squirt holes point [away from the cam] & that the DOT or arrow on the piston head/crown is to the engine front.
Also make sure if he assembled the engine the crank turns firmly but with no undue dragging. _________________ John GIBBINS
ASE Master Medium/Heavy Truck & Auto Technician 2002 USA
Licensed Motor Mechanic NSW # MVIC 49593 Current
YOU CAN'T TROUBLESHOOT WHAT YOU DON'T UNDERSTAND
Joined: Apr 08, 2009 Posts: 249 Location: Mariposa, Ca.
Posted: Sun Sep 11, 2011 11:12 pm Post subject:
The last two items I know are good. As I got this back as a long block, I could see the piston alignment was/is correct and the crank turns smoothly. The con rods, if turned around in relation to the piston orientation, could still be mated to the caps correctly but not facing the direction you would expect. Don't know if that would affect the oiling or not.
At least that is what I am thinking. I trust this guy to the extent he knew that something was odd when he tore the engine down and tried to correct it on the build side. I just don't know if the con rods were installed opposite on two cylinders a long time ago. This engine ran for many miles in that condition and did not have a knock when I got it. All the crank needed was a polish.
I also don't know why he might not have checked further what was going on but I am hoping there will not be a problem on start up. He is a busy shop and I sense he did not want to spend a lot of time trouble shooting a problem that may not actually be a problem, but only a procedural difference. Keeping my fingers and toes crossed.
One only needs to peruse this web site and the G503 web sites for a few hundred examples of big headed professional rebuilders turning out improperly rebuilt and/or assembled simple L134's.
I have posted to this topic several times and my advice is still the same wether you have a 50 year old starter or a 50 year old L134 you must research the builder's history and reputation. When satisfied he is the one that you want to build your engine, starter, generator or carb. the next step is to ask him bluntly if he can show you his copy of the technical manual required to accomplish the rebuild.
In some cases the ability is there but the tech manual is not. Then it may help to bring a copy of your manual for the prospective builder to use as there reference. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Feb 20, 2007 Posts: 606 Location: Illinois
Posted: Fri Sep 16, 2011 7:58 pm Post subject: All Ok
I dropped the pan on my M38 motor and verified that the rods were all Ok, in proper position 1-2-3-4, shallow side towards the crank bearing, oil squirt holes towards distributor side and piston T slots towards the manifold side. No issues with bearings or interferance from other parts. No chunks of metal in the oil pan. I did recover a very slight amount of metal dust from the pan, less than what would cover a fingernail. Could have been from the rebuild process or some of the other work that was done prior to it being buttoned up. I'll monitor that through break-in. So all is good.
A big thanks to WesK for the heads-up! I thought everything was Ok the last time the motor was open but I didn't specifically check the oil squirt holes. Better safe than sorry! The photo of the opened engine I posted was not shot square on so it may have looked like the rods were out of position.
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