MTFCA Forum

I am working on customer engine out of a Speedster. Pulled rods and pistons finding this.
Rods # 1 and 4 heavy rods
Rods # 2 and 3 light.
?
Was this for some kind of balance job?
Anyone seen this before? Thanks Dan

They all need to weigh the same. Best to check big end and total weight to see how much variation you have. How did it run? Probably a lot of vibration at speed, unless by some miracle they all weigh out the same. Was there any evidence of any balancing on any of the engine parts? Could be its just a "put it together and see how lucky we are" situation or "its just a Model T".

The engine I'm building for my speedster had heavy rods on 1 and 4, "X" rods AND tin can pistons on 2 and 3. That had to run smooth!

I've seen nos 1 and 2 weigh the same and 3 and 4 the same

Interesting discussion. I'm in the middle of replacing a rod I wrecked in my 23. I ordered a re-babbited rod bored to my crankshaft and just got it today. It's an aftermarket "light" rod but weighs 569 grams compared to my Ford script rod at 486 grams (without bolts or nuts). After discussion with my supplier, I'm sending both the new one and the old one to him to re-babbit and bore to fit my .015 under crank. I expect that 83 grams, nearly 3 ounces heavy, at 2000 rpm might shake a little. I did check the rest of the rods and they're all Ford script, but I did not pull them and weigh them.

When I have rods poured or even bought, I balance a set of 5. This maybe why I have not needed an extra rod. (Yet)
Kind of a reversed Murphies Law deal.
If you have a spare, you will never need it.

All I do is model T engine rebuilds, I've never come across a matching weight set of rods yet in the 100 odd years of people trying to keep them going, even 1 or 2 cylinders being bored or crank journals ground different sizes.
Overseas parts books offered 14 piston sizes, USA only 5 sizes.

That sounds familiar. Years ago I bought a shop full of Model T parts, short blocks pieces and parts.
One block looked pretty good and the crankshaft and rods seemed pretty good and tight BUT no. 1 and 4 had the older heavier rods and 3 and 4 were the lighter and newer rods. I still have the block! This type of “balance job” has been done before it seems!

Seen it many times. A reasonably good balance can be had by putting matching rods on 1 & 2 and different matching rods on 3 & 4. They spin opposite with matching weight together. However, numbers 2 & 3 reciprocating weight will result in added forward and backward stress through the center main, and theoretically could result in an eventual crankshaft fracture. Which in reality is so likely regardless of what you do the added stress may in fact be inconsequential.
Matching rods on 1 & 4 and again on 2 & 3 (different from 1 & 4) will result in significant shaking at even moderate rpm.

Proper balancing of rods requires all four rods match on the crank end only very closely! The individual overall weight between all rods needs to be very close. AND the rods and pistons as a unit need to be very close as well. I made and use a simple rod balancing "scale" (no numbers, just relative balance between two rods) to get the crank end extremely close.
Since I am usually refitting used rods, I often mix in earlier heavy caps onto later lighter rods for initial closeness. I then grind surface roughness and forging excesses to get rods really close. Final closeness is achieved by mixing hardware. Slightly longer bolts, heavier or lighter nuts, sometimes a washer or two. I even use different size cotter pins to bring them in that final tiny amount.
I then check and to some extent correct piston ends and rod's overall weight. Final total weight I can trick a bit by using very minor differences in the weight of the pistons which are matched very closely beforehand. I put the heavier piston on the rod that needs a small amount of weight.
Final overall weight after the pistons and all sections of rods have been gotten as close as I can get them, might be a few small holes drilled in the piston skirts below the bottom ring.

I also usually do five rods for an engine I hope to keep and use. A matched ready spare that may not be quite as precise as after all the detail foolishness? But will be so close that nobody would notice the difference.

Having done several engines for myself, I have balanced a few dozen connecting rods over the years. It is amazing how much Ford rods can vary in weight! I have one beautiful connecting rod that looks exactly like a hundred other 1920s rods. But it is so light in weight that I have yet to find another rod that will match it. I can't bring myself to add enough weight in potentially bad ways. So, it hangs on a hook on the wall

Have not seen the engine run, had a cracked block.
The 4 rods have matching machine marks. So don’t think it was a put together and see what we got job. The work on the rest of this speedster is too good for that.
The crank is not a std size. Rods measured 1.230 just like mains. So it was ground that way. Rods were poured and all machined the same.
I plan to check balance on the rods today and see if 1 and 4 match and see if 2 and 3 match.
Was just wondering if anyone has seen this before.
The car was supposed to come from Houston Tx area. Built by someone in the aerospace or airline field. Anyone know anything about itit? Thanks Dan