F-Head Engine Issues

Ok, so I have dubbed the ranch hand a 63, only because from all the information I can gather it falls in the 57 to 63 range. The issue that I am having now it that I pulled the oil pan and the #4 rod was loose on the crank journal, hence the knock. The engine had good power once I got the compression to come up and adjusted the timing, point gap and valves, but the knock persisted. The rod journal on the crank measures to be 1.910" and the info in the book said it should be 1.933", could the journal have been worn that much by the bearing? There are also some light scratches on the Journal and the bearing. Bottom line, can I repair the engine in place or do I need to pull it and do a full rebuild?

 

If you want to do it quick and dirty you could maybe slip in some undersize bearing shells. May help the oil pressure, etc. on a temporary basis.
Use some Plastigage to check the fit.

This will give real mechanics the heebie-jeebies, but I've done it a couple of times under the shade tree. Not perfect, but might reduce the knock and slow down any further damage if you treat it gently and don't expect to use it much at highway speeds.

Save the full rebuild for the next time around?

 

Didn't pull the other three caps or mains, I was just looking for the knock culprit. The journal is not egg shaped or oblonged and the compression is 125 - 120 - 130- 130.
The Jeep is going to spend the rest of it's days working on the ranch, low rpm and slow speed for the most part, I just dont want to brake the rod if the RPM's do get up, and the knock is disturbing......
The rod had side to side play before I pulled the cap but only the middle of the bearings showed any wear. Is it unreasonable to think that someone inadvertantly put the wrong bearing in this rod?
Also, is 1.910 a standard size? I would think that +.020 bearings would work if the actual original standard is in fact 1.933. The bearing I took out was .050

 

It's a forged steel crank, so you may be able to replace the bearing and it will be ok.

You have to do something about the knock, whatever else you do.

The journal diameters will be given in the FSM (factory service manual). Do you have the FSM? Reprints are widely available and fairly cheap. The M38A1 manual is online and may be helpful https://archive.org/details/M38a1EngineAndClutchManual - it probably lists the crank journal dimensions, but I don't have time to page through it right now.

 

Ok, so all the data points to the standard size for the connecting rod journal to be 1.9375 and the oil gap being from .001 to .0019. If my journal is 1.910 that would be .0275 diffrence from standard so a .025 undersized would be very close to ideal, but there seems to be no such animal.......
Question for the f 134 master in the crowd is this: If I put a .020 undersized on this crank it will leave a .0075 oil gap. Will this eventually lead to another knock and failed bearing or will the extra clearence make that big a diffrence? And the real question....... Did I screw up the measurements or did the crank get turned down too much on that journal? Trying to save time and Money, most times you can't do both.........

 

In Andy Granatelli's book "They Call Me Mr. 500" there is a story about shimming main and rod bearings. http://www.amazon.com/They-Call-Me-Mister-500/dp/0809296357

 

When I was 13 yr I shimmed my first set of rod and mains in a chevy 6 cyl. It was standard practice in the early 50's. We hand ground and lapped the valves with a round wood rod with a rubber suction cup on it.

 

Good news...... It appeares that some time in the past the number four journal was truned down and the others were not??? Then someone replaced the rod bearings on the #4 with STD size bearings as opposed to .020 under. Bottom line, I'm going to replace the #4 bearings with +.020 bearings, check the oil gap with plastigage and hope it all works out.
Thanks for the info.

 

Wow. Sometimes the jeep gods are smiling.

 

Well the jury is still out on that.

With .0075 clearance, there are a couple of problems that may occur, one being that is enough space to cause it to rather quickly regain is lost sound effects. And two, I would be concerned about that clearance and its effect on the rest of the oiling system. Especially the rocker arms/shaft.

Is the potential fix worth a shot? For the use, perhaps. But pay close attention to the oil pressure.

 

They still make shim stock.

 

Yes, but I see some problems with that in this case. To get the clearance close, .0025" shim stock will be needed and that is pretty thin for any structural strength. Since you still need approximately .002" clearance for proper lube, how do you keep that shim stock centered on the rod journal and not start to work its way out to one side or the other where it will promptly be digested into little bits of abrasive for the rest of the engine? You still have to have the side clearance.

I've worked on a number of engines that do use shims to set rod bearing clearance and each and every one had the shims between the rod and its cap, secured by the rod bolt. And every one of those, you needed to remove shims to adjust for wear.

To do this right with some expectations of normal wear, there really isn't another good solution other than getting that journal turned unless you can find someone to make a custom bearing. If you have enough money to throw at it, I'm sure you could find someone to make that bearing. Cost effective? Probably not.

 

I could picture the shims working. On one hand. my thoughts are that the "bearing crush" allowance would pin them in pretty tight. But on the other hand, what effect would a shim have on the crush specs?

On the third hand, anything will be a big improvement on what it was, shim or no shim.

See what story the plasti-gage tells...

 

Take a look at Deckwar tappered shims.

 

Perfect.

http://deckwartaperedshims.com/main-bearing-shims-product-info.php

 

Back in the old days, we get the rod cap on a glass sheet and use 800 wet&day sand paper. We do figure 8 and we could tighten 2 0r 3 thousand.

 

Sounds kinda permanent. Unless you mean with poured babbitt bearings.