218 vs 230

[pflaming]

I learned today from Vintagepowerwagons that the differences between a 218 and a 230 are the rod length and the crankshaft. The blocks and the pistons are the same. Interesting. He also said that one of the primary reasons the bearings went out was because the pistons, rods, and cranks were never weighed and matched and that the original castings could be off by over an ounce per piston. His advice was to find the lightest one then take a dremmel and grind out material from behind the skirt to get them within a gram of each other. The result, he said, would be noticable in smoothness and in longevity.

This is probably old news to many, but then a reminder now and then does no harm.

[JBNeal]

Yet another reason I'll be tearing down the '48 in the coming months. When I rebuilt the motor in high school, #6 had a stuck ring that I managed to remove after taking a chunk out of the piston itself. I replaced the piston with a new one, but I didn't weigh any of them. The engine has a vibration at 45mph that I suspect is rooted in the piston area, so I self-governed my speeds to 40 and it ran decent. But the long-term effects of an unbalanced engine ain't too pleasin', so I'm gonna try to nip it in the bud.

[Plymouthy Adams]

evidently he is speaking just from behind the counter salesman....for if you read your own manual you will see just what went into the balance of these engines..without calling names and such I must say there are folks out there who's very livelihood depends on selling you parts and oft times some snake oil...

factory pistons are within +/- 2 grams of each other...and cautions that any new piston installed thus referencing a broken/mismatch set..that it also be matched in weight..also never test fit a piston with the pin installed...yes the factory tolerance is such even this can throw off a measurement..these engines have not lasted all these years without attention to balance from the factory regardless of the so called specialists...they are blowing smoke saying otherwise..

[pflaming]

Tim: ". . . never test fit a piston with the pin installed. . ." (1) when I get my set I will weigh them and see how they match, (2) going to weigh the old set also, (3) going to test fit in the cylinders before I attach to the rod.

VPW said the new pistons and rods were very consistent, his statement related to original parts. Whoever is right is not important to me, that things should be checked for balance thus reducing viabration is what I learned.

[Flatie46]

evidently he is speaking just from behind the counter salesman....for if you read your own manual you will see just what went into the balance of these engines..without calling names and such I must say there are folks out there who's very livelihood depends on selling you parts and oft times some snake oil...

factory pistons are within +/- 2 grams of each other...and cautions that any new piston installed thus referencing a broken/mismatch set..that it also be matched in weight..also never test fit a piston with the pin installed...yes the factory tolerance is such even this can throw off a measurement..these engines have not lasted all these years without attention to balance from the factory regardless of the so called specialists...they are blowing smoke saying otherwise..

I've put a few engines together but never a flathead 6. I know I always warm the piston in the oven to expand them then the pin would slip in nice and easy. I don't understand what difference the pin would make in a test fit.

[John-T-53]

The pistons in my 218 were balanced with their respective pins...when I got the parts back from the machine shop I was told not to mix up the pistons and pins.

[Flatie46]

Oh the weight of the pins. I was thinkin' Tim meant it would throw the test fit off somehow in the bore.

[pflaming]

". . . I always warm the piston in the oven to expand them. . ." Question: 'rule of thumb', how long, how hot?

[TodFitch]

Long post. Please accept my apology in advance.

The 1933 Plymouth owners manual has a bunch of specifications in the back. Weight variation for pistons is listed as no more than 1/4 oz. (7 gr.) That was before they stroked it to make the 201 engine. Seems likely that they would tighten up that specification as the years went by so I'd believe that being within 2 gr. or so by the 1940s would be reasonable.

Back in the 1975-77 time frame so I lost a piston. The top ring land and ring broke and a piece of piston ring got on top of the piston. There was not enough clearance between the head and the piston with the piece of ring there. That cocked the piston sideways and broke the skirt. Fortunately the bore in the block was not damaged. This happened 300 miles from home.

I called Egged to order a set of pistons and rings and once the parts arrived took the Friday night Greyhound bus back to my sister's where the car was parked. I had Saturday to build up the engine and Sunday to drive it home. With my then brother-in-law we took the rods and new pistons to the machine shop located in the physics building on campus (he had privileges to use the facility) and we set about fitting up the pins. We found that the new pistons, in addition to weighing a lot more than the original factory pistons, varied by much more than the 1/4 oz limit in my documentation. Neither of us were experienced enough to know where to safely remove material from the heavier pistons. And we knew that there could be problems putting unbalanced pistons into the engine.

It occurred to me that in the L-6 engine pistons move up and down in pairs. So I sorted the pistons by weight. The heaviest and lightest I paired for cylinders 3 and 4. The next heaviest I paired for cylinders 2 and 5 with the light one for that pair adjacent to the heavy one from the 3,4 cylinders. The two pistons that were middle weight went into cylinders 1 and 6. Turns out that each pair was within the weight limit variation with each other. So the pistons on each throw of the crank weighed the same. And the pistons in the front of the engine weighed the same as those in the rear.

The engine ran smooth with it that way. Drove it cross county and only decided to rebuild it correctly as part of the overall restoration of the car.

I would not recommend this as "good practice", but you can sometimes get away with things if you have a good mental model of how it all goes together.

[Flatie46]

". . . I always warm the piston in the oven to expand them. . ." Question: 'rule of thumb', how long, how hot?

I like em lightly toasted but not burnt. Hee Hee I couldn't resist. I'll set it on a low temp and have them just to where you don't want to hold em bare handed. I also put my pins in the freezer for a while until right before I'm ready to put em in. It don't take much heat really and if they don't slip in warm them a little more.

[John-T-53]

My pins slipped right in the pistons at room temp. The fit was not tight enough to warrant heating and cooling of the parts. I could use my thumbs to move the pins in and out....is that too loose? Hmmm...

[Merle Coggins]

My pins slipped right in the pistons at room temp. The fit was not tight enough to warrant heating and cooling of the parts. I could use my thumbs to move the pins in and out....is that too loose? Hmmm...

No, that's just about right. Mine were the same.

Merle

[pflaming]

When I asked a mechanic friend how to remove the pins, he asked if they were 'floating' pins. If not he said I may have to press them out. So if the do/may be put in 'easily' they then are 'flaoting' pins thus the snap rings on both ends. Is that a fair assessment?