Low compression

[Malcolm Towrie]

Originally Posted by Lynn Eades

Malcolm, What model is the engine? What casting numbers if any? Does it have domed pistons? What cylinder heads does it have? What bore size? (just checking)

Lynn, yes, it has domed pistons. CR is 6.12:1.
Stock bore size is 3 1/16", 3.0625". This one is 0.015" over so 3.0775".
It's the 85 HP, 221 cu. in engine. I'll get some casting numbers.

Malcolm

[Malcolm Towrie]

100% agree with you, Richard. Ever since seeing fresh Shell Rotella T 15w40 (a very popular diesel oil loaded with detergent) turn black within a few miles on one of our Ferrets, I've had my doubts about the wisdom of using this oil in our old engines.

And since then, I've seen how much sludge accumulates in the oil pans of these old engines. In fact, I suspect the oil pans were made so deep just to provide a nice quiet place for particulates, varnishes, etc. to settle down into out of the way to somewhat compensate for the lack of filtering. Dissolving this stuff back into a high detergent oil is bad news.

Malcolm

[Jim Burrill]

HD oil issues - My Humber Mk4 Armoured car had an engine rebuild at the shop in the UK. With less that 50 hours of run time, we burned up no4 Main bearing.

The final understanding was that during the engine rebuild, two oil channels (which has a freeze plug type cap on one end, and a bolt on the other) was not opened and cleaned out.

We put HD oil in for our running in.

Apparently, it dissolved the sludge and circulated it to the oil sump/pan. The pick-up for the oil pump has a metal wire filter. That was completely sludged over. The resulting oil starvation caused #4 piston main bearing - a poured babbet bearing - to melt.

We had a machine shop remove all the babbet bearings and switched to cap bearings.

We are better off having cleaned the oil journals, but some $4,000 poorer for having to pull the engine and the rebuild.

So.... no more HD oil for my stuff!

[Malcolm Towrie]

Jim, based on a similar bad experience I had, I'd be more inclined to blame the shop than the oil.
I had a local shop do machining on a Chevy engine. As normal, they hot-tanked the engine first. But, like your shop, they didn't remove all the gallery plugs and flush/brush the galleries out. Luckily I noticed when I got it back. I removed the plugs and found a large amount of sludge behind them that had been softened to a semi-liquid by the caustic cleaning solution. I shudder to think what that stuff would have done to the new bearings as soon as the oil started circulating.

Malcolm

[Malcolm Towrie]

Originally Posted by Malcolm Towrie

Lynn, yes, it has domed pistons. CR is 6.12:1.
Stock bore size is 3 1/16", 3.0625". This one is 0.015" over so 3.0775".
It's the 85 HP, 221 cu. in engine. I'll get some casting numbers.

Malcolm

Lynn, I couldn't find any casting numbers, strangely enough. This is a 24 head-stud engine.

[Michael R.]

On Canadian produced engine blocks found in universal carriers MK-I* and MK-II*, the engine block casting number is displayed on the shoulder over the water pump. Viewing from the front of the block, the 'left side'. The number '81' casting plate may appear as '87'. (see image of two examples)

Serial numbers on Canadian produced engine blocks found in universal carriers MK-I* and MK-II*, the number being displayed on the exposed portion of the intake manifold deck. Viewing from the front of the block, the 'right side, rear corner'.

Serial number format is 'TLXXXXXF'. There may be multiple 'F' letter strikes after the normal sequence, as well as the inspector stamp and additional letters or symbols, the more common upper case letters being 'E' and 'V'.

The complete serial number example displayed belongs to the engine found in the restoration thread for the carrier in Israel, with thanks to Mr. Berko. Of note, that is a MK-I* carrier, upgraded to MK-II in the UK and given a British cast data plate, with a MK-II* engine block.

See: http://mapleleafup.net/forums/showpo...7&postcount=70

[Malcolm Towrie]

Thanks, Michael. I found the "81" but only because you told me where to look. The cast number is almost illegible.
I didn't find a serial number of any kind. I did find a brass plate identifying a rebuild by RCEME in 1951.

I've got 9 valve/guide assemblies out and two pistons so far. Everything looks in good condition.

Malcolm

[Lynn Eades]

Thank you Michael R, for educating me on carrier engine numbers.
Malcolm, I am trying to get to the bottom of your low compressions (in the apparently good cylinders)

Ford did 3 different piston tops:
the flat top piston is for the early 21 stud engines.
There are two left:
The first is a sperical top. The profile when looked at from the side is a gentle curve going up one side over the center and back down.
The other is what Ford called a "Combination" When observed from the side it appears that the climb is a constant flat, coming to a point at the top and straight down the other side.
These pistons are not interchangeable.
The sperical one Part no 78C-6199-A
There are a couple of combination pistons.
If you look inside the piston skirt and you should find a number like 01T-6110-A

Cylinder heads. Some types fit both sides but mostly there is a left (6050) and a right (6049)
They may be hard to see, but as far as I know, they are all identified with part numbers
Those numbers above are the base number. All have prefixes and some have suffixes.
Your engine could/ should be wearing heads with:
81A-6049-A (or 6050)
81T-6049
C91A-60xx- B1

On compression ratios:
At sea level a comp. ratio of:
5.4:1 = 99psi
5.6:1 = 102psi
5.8:1 = 105psi
6.0:1 = 108psi
6.2:1 = 111psi
6.4:1 = 114psi
6.6:1 = 117psi

The above is all drawn from Ford service bulletins.
The whole point of my post is so that you can check that the combination of pistons and cylinder heads is a match.
In 42 the valve line changed. (design) Early heads could be relieved to fit the later blocks. If these heads were fitted to an early engine, they would have a lower than std. C.R.
Food for thought.

[Malcolm Towrie]

Thanks for the good info, Lynn. I'll check out what pistons and cylinder heads I have.

But I found something else interesting. I only managed to get one exhaust valve/guide assembly out. (The others are stuck in the block, apparently a common problem with flathead Fords.) Looking at the seats with the valves fully open, I flagged this exhaust valve as OK. (It's on one of the "good" cylinders.) But check out the photo taken after I cleaned it up. It's far from OK. It's blackened and pitted. Compare it to the photo of a good intake valve face. I'm beginning to think the whole low compression issue is down to bad exhaust valves.

DSC00591.JPG

DSC00590.JPG

If penetrant doesnt loosen up the stuck valves, I'll have to make up the c-clamp tool to get them out.

Malcolm

[Malcolm Towrie]

Well, live and learn. I've only checked one rod bearing but I found it way too loose in the rod bores. (Two rods install on one bearing.)That's normally a recipe for disaster as if the bearing spins in the bore, it will damage the rod, bearing and crank. But turns out its normal for flathead Fords. They have "floater" rod bearings. Unlike typical rod bearings which are locked tightly in the rod bore. they ride on an oil film in the rod bore as well as on the crank journal. Trouble is the bearing I checked is 0.020" oval (2.030" at split line, and 2.010" 90 degrees around) so it's too snug in the 2.220" rod bore. The fix is to "massage" the bearing to make it round again. Sounds fiddly.

Also, anyone any idea what the recommended torque is on the rod nuts? The manual doesn't say. They're secured by cotter pins so on disassembly, I found the torques all over the map depending how much the previous rebuilder had to over-torque them to get the cotter pins in. I guess I'm looking for a minimum torque.
Malcolm

DSC00589x.jpg