318 LA rebuild after losing a valve seat

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Balance? In the early 1970's ---- 318's had a light con rod and then went to a heavy con rod.
 
Righty Tighty said:
Well, finally had some time to get some work done on the block. Chased the threads and cleaned it one last time before installing the mains and crank. Then moved on to the pistons. Would ya know it, I screwed up and bought the wrong rings. The Sealed Power H814CP pistons call for a 5/32” wiper, not a 3/16”.

As a first time builder, I really want to thank this forum and especially krazykuda for his build tutorial. Also Pete’s Garage on YouTube has been incredibly helpful. I’ll post updates as they happen. View attachment 1715469561
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I hope to be doing some more how to rebuild articles soon...

Hopefully in time to help you...
 
no- just do not replace early with late and vice versa- changes balance
you have closed chamber heads which gives a compression bump
you will have no quench but you did not have any anyway
calculate compression with all 3 gasket thicknesses
let's get it together
 
Gotcha. I kept the stock rods but replaced the pistons with higher compression ones. Part of the reason for this rebuild is that my stock pistons were ruined, decided to change it up a little while I had everything apart.

I’ll be calculating the CR soon as well as CCing the heads. Will post the results when I get them.
 
Righty Tighty said:
I’m not quite getting what you’re saying. Are you suggesting I balance the rods?
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No, I'm saying that because two different rods were used, that two different crankshafts were used for balancing the motor.
The light duty con rods are marked #1619699
The heavy duty con rods are marked #3418645 or #2899495

That crank looks similar to a 340 cast type. But it may be for a 318 with the heavy rods. I don't know. After you choose the pistons, I'd bring a piston, rod, rings, piston pin, and rod bearing to a machine shop and have them check the crankshaft balance to see if it is close.

Measure the crank end play before putting the cap on. It should be the same after you torque the cap down.
 
pt70 said:
After you choose the pistons, I'd bring a piston, rod, rings, piston pin, and rod bearing to a machine shop and have them check the crankshaft balance to see if it is close.

Measure the crank end play before putting the cap on. It should be the same after you torque the cap down.
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Well ****. The crank is already installed. How crucial is it to check for balance? FWIW, the crank I bought was a reman supposedly for a '71.

I'm not keen on removing it because the fasteners I used are torque-to-yield, and they weren't cheap. From what I understand, TTY fasteners should only be torqued once. At the risk of beating a dead horse, this is my first rebuild, so everything here is a learning experience.
 
Where did you get these tork to yield fasteners
never seen them for a SBM
mfg and part number please
if you use 71 vintage rods- whatever they were heavy or light- someone can post where the break was
and your pistons and pins are close to stock weight you are good to go
IF
you did change rods from 71 then weigh the big end and the small end and weigh the pistons old and new and let's see where we're at using the weight of the big end plus half the weight of the small end plus piston formula
and compare
maybe you get luck with a heavier rod but lighter piston (and pin) :)
 
Maybe I was mistaken, they are the ARP 140-5002 studs. For some reason I thought they are torque to yield?

The rods may be 73, as the block is a 73, I don’t know if that makes a difference. I’ll check the numbers on the rods tomorrow. The pistons I have are the Sealed Power H814CP.
 
if you can read the number on the crank someone will know what year and source it is
glad you have both sets of rods
hope you are ok without a balance job
Your are good to go on the torque to yield issue
check your back and forth free play?
get the thrust cap lined up with the block :)
(both thrust faces lined up)
take a light and check
the fix would be easy
 
The balance change going from light to heavy rods is not all that much; I have made the computations before. It only changes bobweight by 20-30 grams. I don't think Mopar even changed the crank to compensate.
If this is the crank and rods that came in the car, then I would not worry over this matter. The crank is a cast one and that was what was used with both size rods from what I have been able to gather.
These pistons and pins are weighted to be used as direct replacements with no re- balance.
So this combo ought to be as good as factory balance.... Which is not to hotrod standards but it is not 'off'.
OP, what do you mean by TTY fasteners? Stock parts are not TTY.
 
RustyRatRod said:
No way in the world that will ever cause the valves and pistons to intersect.
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Yes that is pretty mild for lift and duration, and these pistons will be about .070" in the hole. I'd put it together and just snug the heads bolts on one side with clay in there, rotate the engine 2x, and see. There are some things you need to do with the hydraulic lifters on the cylinder being checked to be accurate.
As for the pistons, you can only get slightly better for stock replacement types. I'd prefer some KB's, but there is no known 318 performance pistons out there right now that you can put in without a mandatory re-balance. So for a dirt simple build, you have no better choices.
And, OP, triple check your oil passage plugs everywhere!
 
Wyrmrider said:
if you can read the number on the crank someone will know what year and source it is
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Here are the numbers on the crank. I don't know if I mentioned it before, but the crank was a reman from one of the big chains. Ordered it for a '71 .030" under, since I hadn't realized the block was a '73. I don't quite know why I bought it .030 under, other than my old crank was .030 under. Seems I cut myself short of some life on the crank by doing that.
6T46HtpjS%qU6XDWXHNOGQ.jpg

nm9stheham said:
The balance change going from light to heavy rods is not all that much; I have made the computations before. It only changes bobweight by 20-30 grams. I don't think Mopar even changed the crank to compensate.
If this is the crank and rods that came in the car, then I would not worry over this matter. The crank is a cast one and that was what was used with both size rods from what I have been able to gather.
These pistons and pins are weighted to be used as direct replacements with no re- balance.
So this combo ought to be as good as factory balance.... Which is not to hotrod standards but it is not 'off'.
OP, what do you mean by TTY fasteners? Stock parts are not TTY.
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Yes, this will only be a mild build grocery getter. I doubt I'll ever take it to the track other than to watch other people race :D The rods did come with the car when I bought it (crank is new/reman) , but I'm certain the engine was swapped sometime before me. Here are the numbers on the rods. For those with old eyes like mine, the number is 3418645. Also, each rod has a different combo of letters, like CNC, ANE, etc. What does this mean?
18JxetesRpe0y5eB84vRAQ.jpg
TF9i8FpTTEGDpU82QqhGNQ.jpg
 
Those are the "late"rods, the heavier duty rods. They share the same basic dimensions with 340s and 360s.
They will be the same dimensions as what would have come from the factory on your 73 crank.
My "645" rods have been bouncing off the rev-limiter at 7000, since 1999, in my 360. If you keep the engine out of detonation, and the engine doesn't ever gulp water, then they should be the least of your worries.
 
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What about running them with a 71 crank? Unfortunately I’ve done a lot of my purchasing backwards, without knowing my rods, cam, etc. Like the springs I bought weren’t big enough for my cam, and I had to have the guides cut (also due to the cam). I guess that’s the price I’m paying for being a novice. I’ll tell ya this, boy have I learned a lot for the next time.
 
Righty Tighty said:
What about running them with a 71 crank?
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I think that was discussed in a previous post
My literature says that the lightweight rods were retired in 71/72.
And it says that "if you use the HD rods in an engine that originally had LD rods, you will change the balance of the engine. This balance can be as much as 100grams." HP, Books; how to rebuild your SBM/ Don Taylor &Larry Hofer,p45.
 
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No... It is nowhere near 100 grams change! That book is wrong. Geezzz... Now if you weighed the parts and do the bobweight computation wrong AND had worst case variations you still could not get to 100 grams off.....
I have weighed both sets of rods. There is 32 grams difference on average (726 vs 758 grams per rod), which numbers have confirmed by others, and most of it is in the rod beams. If you weigh big and small end weights ( which I have done), most of the beam weight goes into the small end weight. When you compute the bobweight, the small end rod weight is cut in half, as it is part of the reciprocating weight.
So trust me on this one... The bobweight change is in the 30 gram range. I have all the numbers to show it. For a mild street car, it will run OK.
Now if you want hotrod quality, then it ought to be balanced regardless.
 
It does not say the rods are are a 100 gm change. It says the overall change in the swap could be as high a 100gms. Since the late rods are pressed pins, I would assume he's talking about the pistons being on there as well. So, IMO, the swap actually reads ; the 73 up pistons and fat rods which sat on a cast crank, onto the 273/318 steel crank.
 
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AJ....I know the deal here.... Press pins save about 2-3 grams as the pin locks are not there. The pin weights are identical for both: 154 grams before and after the rod change.
No, there is nothing close to a 100 gram change with this rod change in the balance area. And the production 318 LA crank was cast from day 1 for standard cranks, and the 273 used the same cast crank starting in '68. The 273's smaller pistons weigh less so they used 221 gram pins to keep the same bobweight. Both cast and steel cranks in the 318 are the balanced to the same bobweight .... I have never run across a different piston or pin weight for any model.

No more guessing... Bring real numbers if you want to try to convince the OP that he has a balance problem.
 
nm9stheham said:
OP, what do you mean by TTY fasteners? Stock parts are not TTY.
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I think I was mistaken when I thought my fasteners were TTY. I was watching the episode of Pete's Garage where he goes in-depth on fasteners, and he mentioned the ARP bolts. I replaced stock with the ARP 140-5002 12 point fasteners, and I thought for some reason all of the ARP main bolts were torque-to-yield.
 
If you torqued to a final torque, then not TTY AFAIK. All of the TTY's I know of are torqued to a fixed #, then turned a fixed # of degrees, or 1/4 turn, or something similar, without reference to torque value.
 
nm9stheham said:
No... It is nowhere near 100 grams change! That book is wrong. Geezzz... Now if you weighed the parts and do the bobweight computation wrong AND had worst case variations you still could not get to 100 grams off.....
I have weighed both sets of rods. There is 32 grams difference on average (726 vs 758 grams per rod), which numbers have confirmed by others, and most of it is in the rod beams. If you weigh big and small end weights ( which I have done), most of the beam weight goes into the small end weight. When you compute the bobweight, the small end rod weight is cut in half, as it is part of the reciprocating weight.
So trust me on this one... The bobweight change is in the 30 gram range. I have all the numbers to show it. For a mild street car, it will run OK.
Now if you want hotrod quality, then it ought to be balanced regardless.
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I agree, I weighed the difference on my last build, they averaged around 30 grams for each piston rod.
I have the numbers wrote down on a piece of cardboard in one of my garages.
 
nm9stheham said:
If you torqued to a final torque, then not TTY AFAIK. All of the TTY's I know of are torqued to a fixed #, then turned a fixed # of degrees, or 1/4 turn, or something similar, without reference to torque value.
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Oh okay. I torqued to the manufacturer’s spec in a series of three increasing torque settings. Anywhoo, I’ll be getting the pistons in today and moving on!
 
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