TEA20 Rod Bearings

[VectorSix]

Did some checking of the rod bearings and rod journal size (this is the crankpin diameter I am assuming). Here is what I found on #1:

Rod journal sizes measured at various points:
2.084
2.085

Not sure if this is within tolerance, not sure what "clearance new" means.

Bearing thickness:
Fairly consistent at .0675

Appears to be the original bearings, some minor scoring, nothing major.

What do I do with these measurements? Obviously the bearings are worn by 5 thou. Is this enough to cause some low oil pressure and/or light knocking in the lower half of engine? Can I just replace the STND size bearings and be on my way since the crank is showing wear in the 1 thou range? Thanks!

 

[Bob (Aust)]

My experience, for what it is worth, is that within a couple of hours running time new bearings on an old crank will be almost the same as the old bearings you replaced. If the journal shows no scoring etc and the bearing clearance is within permitted tolerance, I would not change the bearing shells. Just my opinion..........

My manual for the 85 mm bore TEA20 says the Crank Shaft Journal (Crank Pin) diameter new should be 2.0861 - 2.0866 inches (average 2.0863) and the bearing clearance new should be 0.0006 - 0.0024 inches (average 0.0015).

Despite being an accountant, I'm not too flash with decimal fractions of an inch! If my calculations are not correct I hope one of the guys here that understands micrometers and imperial measurements will jump in and correct me.

So, the crank journal diameter new is (average) 2.0863 plus (average) 0.0015 clearance = 2.0878 bearing internal diameter.

Bearing internal diameter......2.0878
Your journal average.............[u:9009bde598]2.0845[/u:9009bde598]
Difference/Clearance:............0.0033

0.0033" bearing clearance certainly exceeds the permitted [u:9009bde598]new[/u:9009bde598] clearance of 0.0006 - 0.0024 inches, but I have no idea whether it is enough to cause the bearing to knock?

Don't accept my maths above - I hope someone can check and correct if necessary......

If you had a "knock" in the engine I feel you must find and rectify that specific problem, rather than installing a new set of bearings and hoping for the best?

Bob in Oz
'53 TEA20

 

[VectorSix]

Bob, thanks for your reply as usual. Like I've said in other posts, this is all new to me, so I appreciate all the help you and the other forum members have given.

The knock, of course difficult to describe based on my limited experience and knowledge, not to mention this is a forum, when running was isolated to where the oil pan bolts to the block near #4. Since that is the vicinity where the bearings are I deduced that they may be the culprit.

The wear on the crank, .0033 plus the total wear on the bearings, .005 (bottom) and .0045 (top), I figured gave me total wear of .0128. Is my thinking correct here? Is that enough to cause a faint knocking in the area I described, again, first time newbie. As for the actual clearance using plastiguage to see what the clearing is between the bearing and the journal, I have not yet done that.

Probably what would make the most sense would be to pull the crank, have it machined and get the appropriate new bearings, then I get into a whole new world of mess and expense. Eventually I would like to rebuild the entire motor, I guess I was looking for the easy out by just replacing the bearings to get me by my next year of light/infrequent use. But, what you said is new bearings will just wear to where the existing ones are very quickly. However I do not want to damage, excessive wear the crank wither by doing nothing. Would thicker oil help until I can fix it correctly? New bearings would be a waste of time/money at this point then?

 

[Bob (Aust)]

I'm not a mechanic, so the usual disclaimer - your tractor, you break it!

I really have no idea of how much bearing clearance will cause a "knock". I'm still thinking about your measurements but if you have .0128" bearing clearance (or maybe half that all around?) it seems to me you are well outside the new clearance of .0006 to .0024 - by a factor of what - over six times the new clearance? The manual does not give max clearance.

Wait ........ I'll check the Ferguson manual and see if that lists a max clearance.

Back in 10 minutes.

Bingo! :lol: The figures I gave above are from the Gregory's manual (Australian version of Haynes). The genuine Ferguson Service Manual gives us a little more information:

[b:6f17978f49]Big End:[/b:6f17978f49]
Crank Pin Diameter: ...... 2.0861" to 2.0866" 52.987 mm to 53.000 mm

Bearing Diameter: ......... 2.0985" to 2.0872" 53.302 mm to 52.015 mm

Clearance New: ............. 0.0024" to 0.0006" 0.061 mm to 0.015 mm

[b:6f17978f49]Permissible Worn Clearance: 0.006" 0.152 mm[/b:6f17978f49]

I think your bearing clearance very significantly exceeds that permissible maximum worn clearance???

If you want, send me an email and I will email you a scan of the manufacturer's data page.

I'm not going to try to get my head around those numbers, viz-a-viz your dimensions at 11:15 pm tonight, but you should now be able to easily measure the clearance with a Plastigauge.

I have a [u:6f17978f49]personal[/u:6f17978f49] theory that installing new bearings without machining the crank is a waste of time, as the new bearings will be worn the same as the old after 10 minutes of running. And if the bearings are within specifications, why replace? Personal theory - you make your own decision.

I think you must (a) identify where that "knock" is; and (b) make sure the clearances and tolerances do not exceed the manufacturer's specifications.

If the clearances on the old bearings exceed manufacturer's specifications and/or any sign of scoring or heat, [u:6f17978f49]my personal theory[/u:6f17978f49] suggests new bearings are a waste of money and the crank will need to come out and journals ground.

I don't suppose the crank has excessive end float? Not sure if that may cause a knock? Probably not.........

Bob in Oz
'53 TEA20

 

[dbrew277]

if you have the oil pan off just try to push the rods if they move up or down you know which one it is if not go to autozone and get some plasti gauge and check gap in between the crank and the bearing. i know this isnt what you want to hear but if you have spun a bearing you need to take it to a machine shop and have them grind and polish everything.

 

[Roger in Manitoba]

Here's my 2 bits worth.

I have a tea-20, 85mm bore engine. I had a knock and low oil pressure in the engine. I dropped the pan, and pulled the rod caps off. Cylinders 1-3 are in good condition. #4 however, not good. The bottom half of the bearing didn't look good, and the top half was pounded thin.

I took the crank into the shop, they cut the crank mains down 10 thou (they looked good to me), and the rod journals down 20 thou. #4 was scored bad.

The machine shop also hot tanked and straightend the crankshaft. So, even though it was A LOT more work, in the end, I won't regret doing it. But, I would have regretted no doing it if I simply put in new bearings and ended up with the same (or worse) problem.

But, that's just my 2 bits worth. Like Bob said, it's your tractor.

Roger

 

[dbrew277]

if you replace the bearings you are going to start it and get all exited for a 2-3 min. then it is going to start all over again. you are going to be better off just rebuildig because if you grind the crank and put new bearings and then a year down the road you decide to rebuild it you are going to take it apart again and take it to the machine shop again and they will more than likley redo the bearings. it stinks but you will have a strong tractor for years to come

 

[Bob (Aust)]

You probably don't want to hear this, but in the light of a new day and re reading the dimensions above, I suspect you've found your bearing "knock".

I don't think you have any option but to remove the crank shaft and take it to a machine shop for grinding. Make sure they check it is straight. They should supply the new main and big end bearings, however you will also need new thrust bearings.

Very approximate costs in Australia (prices in US$'s), for full engine overhaul:

Crank shaft grind, $30 per journal: $210
Complete engine overhaul kit, pistons, cylinders, gaskets etc: $350
Professional head overhaul incl skimming and average replacement of valves, seats and guides: $250
Timing chain and sprockets: $150
Clutch assembly, bearings and ring gear: $250

To that you can add a carby kit, possibly distributor shaft bush, starter and generator brushes etc.

How many engines these days can you completely overhaul, back to near new specifications, for approximately $1,200?

I also balanced my engine, took around an hour and cost me nothing, but that is another story.

Good luck!

Bob in Oz
'53 TEA20