Seeking Technical Help: Flathead Engine Top End Wear

[keithb7]

I have posted this on another forum too. I am looking to learn more about my recent findings. I am preparing to pull my 1953 Mopar engine. Canadian 25" block, 3 ⅜ bore x 4 ¼" stroke, netting 228 ci.  Today I pulled the head. I measured and found stock bore bores still.

 

What do you suppose would cause this top end of the cylinder rust?  Sitting for decades in a humid environment? Cylinder 1 was the most prominent. Rust in cylinder 1 seems to travel down past the area where the top compression ring would slide. I would have wagered that a piston ring sliding over that area for the past 1500 miles would have taken that rust off. The scrape in the rust seen in cylinder 1 is from my finger nail scratching it.

 

The engine ran and started very well. Earlier this year I recorded 95-100 psi across all cylinders. Wet or dry, not much difference. I put  over 1550 miles on the engine between April and Oct this year. It made decent power. I got the engine tune dial'd in pretty well and it pulled hills very well. Easy to maintain 50-55 mph on varying hi-way terrain.

 

I can feel some exhaust valve guide or stem wear. Not too bad. Guide wear on cylinders 1,2 & 6 mainly.  I have not pulled the bottom end apart yet. I hope to pull the pistons and rods out. Then perhaps I can further measure compression ring end gaps.

Your comments are appreciated. Thanks, Keith

 

 

 

Edited November 8, 2020 by keithb7 (see edit history)

[keithb7]

After posting this above I tried some scotch-brite to clean up the rust. It came off easily. Seems like it may have developed from the car sitting in my garage for the past 3 weeks unused? Humid air? 
 

I measure about a 0.012 to 0.014 ridge at the top of the cylinders. Here’s #1 again. 
 

 

[keithb7]

@plymouthcranbrookI have a few issues with the engine. Some oil burning going down hills. The rear crank seal is leaking pretty good. Block expansion plugs are leaking. I found excessive scale and rust build up in the lowest parts of the block. 2-3" deep of scale/rust. I wanted to get in there and address these issues. Also learn some skills.  Measure and learn about the actual wear in my bores. Look at valve guide clearance. 

 

I just came in from the shop and using my dial bore gauge. I found .010 of cylinder taper.  Not great. Yet as mentioned the engine ran pretty good. It made decent compression. Wondering if I could hone cylinders, slap in some new stock rings again? Clean out the block. New rear crank seal. New expansion plugs. Then enjoy the car as usual. As my cruiser with years of usable life in the engine still?

Edited November 9, 2020 by keithb7 (see edit history)

[Oldtech]

The machinists won't recommend it but, in my opinion, at .010 you can re-ring it and go a long ways. I assume it has the 4 ring pistons so it won't use any oil. 

 In my younger ( poorer) days I overhauled engines like that and got a lot of miles.  Having said that, if your pistons are worn and need replacing, the boring isn't that much more. 

[keithb7]

Thanks @Oldtech. I also recall doing some research earlier. If I bore the 3 ⅜ engine 1/16 over to 3 7/16" I see that Vintage Power Wagons offer a piston and ring set. They are $185 for all 6 pistons with rings! Thats attractive. Leaving my stroke as is at 4 ¼ I'd have about a 237 ci engine. That is certainly appealing to me.  This idea sounds encouraging.

[Rusty_OToole]

3 7/16 is stock DeSoto/Chrysler size. 237 cu in was the stock size for DeSoto engines in the late 40s. This would make a good motor for your car. Have you checked what a local machine shop would charge to rebore the engine? If the crankshaft checks out good, new pistons, bearings, seals, gaskets, timing chain and you will have practically a new engine.

.007 is the factory recommended wear limit. But if economy is an issue, you can go with .010 over rings filed to fit, and knurl your pistons and it will probably go another 30,000 miles or more.

The rust could be from sitting in a damp garage but for more than 3 weeks. The top of the cylinder was not polished because it is above the rings where the piston has most clearance.

If you do the work yourself with the help of a local machine shop you should be able to rebuild your engine for under $1000 for machine work and parts.

[rodneybeauchamp]

Hi Keith, if mine I would go with new pistons and rings and not reuse the old ones. They have done their service already and sure they might go on for many more miles. 
Just that I had a 40 Pontiac engine failure with a cracked piston after renewing all the bottom end. Result was not pretty at all!

just my two bobs worth

Rodney 😀😀😀😀😀😀

[edinmass]

The oil burning going down hill is valve guides. I agree with the others that a light hone and new rings while not perfect should be fine. New guides are cheap and easy on most engines, as is the valve job. New bearings if available as inserts would be worth doing if not expensive. Today’s oils are much better than the old days. It probably would run 200k on a quick and light overhaul.

[keithb7]

Thanks for all your comments, experience, and suggestions. I’ll pause on next steps until I get the engine pulled completely out. Then I can assess the crank and bearings properly.  Depending on what I find will dictate my plan for this engine.  Plasti-gauge should give me good solid results.  Hopefully I’ll complete the engine and measuring will progress over the next few days. 

[Rusty_OToole]

The pistons are cheap enough, but check on the cost of truing the cylinders before you make up your mind. Also we have much better rings today than they had  in the fifties. If they are NOS pistons and rings you might price a set of the latest low tension moly filled jobs. They reduce friction and practically eliminate cylinder wear which is especially valuable on a long stroke engine like yours,

[Old 30's/40's Mopar Nut]

'HI KEITH,

SEVERAL YEARS AGO I HAD A Q1

 

[Old 30's/40's Mopar Nut]

SORRY, DONT KNOW WHAT HAPPENED THERE...

AS I WAS TRYING TO SAY, I HAD A 1947 DODGE BEHAVING IN A SIMILAR FASHION.

TURNED OUT TO BE A LEAKY HEAD GASKET. FROM THE LOOK OF YOUR PICS,

THE DECK OF YOUR BLOCK LOOKS RUSTY?

[keithb7]

An update: I’ve been picking away at my engine disassembly. Measuring and inspecting. Crank and bearings are in decent shape. The main and rod bearings show between .00175 and .002” clearance. Crank thrust .006”. 
I got some valve seal issues.  Not unexpected. I’ve yet to get a ridge reamer to take the ridge off. Then I can slide the pistons out and see how the rings fare. Mostly out of curiosity and my own education mainly. 
 

The amount of junk stacked up behind the frost plugs was shocking. I plan to take the block to the machine shop for a full spa treatment. I’m leaning toward the 3 7/16” bore. 
 

It’ll get all new bearings and valve guides too. Pistons. Rings. Etc. Timing gears and chain. Valve work. Etc.  

 

So far so far so good. Thoroughly enjoying the experience.