How can I assume the assembly was ever balanced properly? Doesn’t the rotating mass need to be pulled and balanced in order to confrim? This is a complete bottom end rebuild at that point automatically?
318 std piston quench with aluminum heads?
- Thread starter 340inabbody
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How can I assume the assembly was ever balanced properly? Doesn’t the rotating mass need to be pulled and balanced in order to confrim? This is a complete bottom end rebuild at that point automatically?
mygasser
Well-Known Member
you can't and yes you need to pull the rotating assembly to check it unfortunately.
You have to pull the crankshaft and piston/rod combinations. The machinist will weigh your piston/rings/pin/and retainers separate from you con rods. Then he will weigh both the big and small ends of your con rods.
The weights will give him the “balance factor.” Then he will spin your crankshaft on his dynamic balancing equipment.
The reading will instruct him to add or remove weight from the bob weights to achieve acceptable harmonics.
No heavy metal required and you’re likely into the balance $300.
Hone your block and reinstall the rotating assembly with your bearings and rings.
Essentially your “ freshening up” the short block.
Aka changing the socks…
@340inabbody If your rocker arms don’t look like this, they should. Get yourself a set of 273 rocker arms and let that son of a ***** run.
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I rebuilt the top end and have those! It’s a sold lifter set up. Thanks for all the help. The information on how much some things will cost is very helpful!!! I want to reduce the compression as I was getting about 205 psi across the cylinders. Also it’s an unknown cam which may or may not be the right one. So finding a decent shop that will work with me will be important. Not sure many are left here in the Phoenix AZ area.
If you can, develop the cam profile before you disassemble the short block. Check your .050 lift for and aft on the intake and exhaust lobe. You may be advanced a few degrees.
Second: your TRW’s are open chamber pistons, so your quench is well beyond min .040”. You can go .010 thicker on your head gasket for cheap. Between the CL and head gasket you may get down to 185~190 psi. Perhaps your a little “short” on duration as well…
James Clews
Well-Known Member
Back in the mid seventies (that's when I had plenty of hair but not so many brains) I built a 360 up for my Australian Valiant Charger as per Hoovers Mover style. I was given a set of pistons out of a brand new 340 so as per instructions had them turned down fifty thou, had the assy balanced and only put a std 360 cam in it . The engine was so high on compression I had to run it on a 50% avgas mixture to stop it from pinging ! It ran unbelievable qtr mile times 13.6 sec qtrs, yes with a std cam and full exhaust.
But the engine was rough! My father would not let me run a reground cam as he said it would destroy the rocker angles and would be a waste of time so I ordered a billet cam from the states which took about six months to arrive. I was fed up with the vibrations so when the cam arrived I pulled the engine down.
I eventually found out that Hoovers Movers used the later nine to one pistons and the pistons I got were from Chrysler Australia's still born bathurst destined 340 program and were 10 to 1 high comp pistons and when I sent the assy back to the machinist for rebalancing he found that the balance was alright but the guy that machined down the pistons in the first place was terrible and the piston heights were all over the place and this would of been the vibration. He machined the pistons down further and rebalanced and I put the engine back together this time with the billet cam and it became smooth again.
So check that you have not got uneven piston heights as uneven compression will cause just as many vibrations as a unbalanced motor!
But the engine was rough! My father would not let me run a reground cam as he said it would destroy the rocker angles and would be a waste of time so I ordered a billet cam from the states which took about six months to arrive. I was fed up with the vibrations so when the cam arrived I pulled the engine down.
I eventually found out that Hoovers Movers used the later nine to one pistons and the pistons I got were from Chrysler Australia's still born bathurst destined 340 program and were 10 to 1 high comp pistons and when I sent the assy back to the machinist for rebalancing he found that the balance was alright but the guy that machined down the pistons in the first place was terrible and the piston heights were all over the place and this would of been the vibration. He machined the pistons down further and rebalanced and I put the engine back together this time with the billet cam and it became smooth again.
So check that you have not got uneven piston heights as uneven compression will cause just as many vibrations as a unbalanced motor!
I wonder if he ran any C12 through it yet?
Hey @Illahe your mail box is full
I know. I’m not a Gold Member so my dm’s are maxed out. I don’t see a delete option…
You have to go in there and delete them individually.
I’m sure there is a better way but I don’t know it.
I don’t see an option for deleting on the message page. I sent a message to Toolman Mike to see if there’s a way to clean the box out.
Here is How to delete conversations from your inbox...
Click the envelope on the top right, then click SHOW ALL
You can also go to your conversation list and click to open one and below the title are some options.
Click on "Leave" and follow the options.
Click the check boxes of the conversations you want to delete
A menu will come up on the bottom of the page - Choose LEAVE CONVERSATIONS then click "GO" (that is the same thing as delete)
One more thing to do. A box will come up once you press GO asking if you want to Accept or...
Click the envelope on the top right, then click SHOW ALL
You can also go to your conversation list and click to open one and below the title are some options.
Click on "Leave" and follow the options.
Click the check boxes of the conversations you want to delete
A menu will come up on the bottom of the page - Choose LEAVE CONVERSATIONS then click "GO" (that is the same thing as delete)
One more thing to do. A box will come up once you press GO asking if you want to Accept or...
if you want to do several at a time: select the box that's to the left of replies and participants. once that is done the action bar will pop up at the bottom (continue selecting as many as you want), then in the action bar click on "choose action" and scroll up the list to "leave direct messages" and select that, then click on GO. you then get a pop up that says: allow future messages or whatever, and you can accept or deny.
well, now's your opportunity to correct all that and ID the cam at the same time!
Happy New year to all on here!
That's a 318 Poly forged crank so a premium part indeed, it has nodules on the flange.
Poly 318 fully floating rods are the same as 273 and are the lightest.
Its the rods that are a problem, probably later forging and are much heavier.
Then you have a different weight piston so a re-balance would have been a 'must do'.
How many folks rework their 318's and never have a re balance done?
Piston change has the least affect, but a rod change is a huge one.
The different rod bolt nuts is a sign of something amiss
That's a 318 Poly forged crank so a premium part indeed, it has nodules on the flange.
Poly 318 fully floating rods are the same as 273 and are the lightest.
Its the rods that are a problem, probably later forging and are much heavier.
Then you have a different weight piston so a re-balance would have been a 'must do'.
How many folks rework their 318's and never have a re balance done?
Piston change has the least affect, but a rod change is a huge one.
The different rod bolt nuts is a sign of something amiss
Ok so I am getting ready mentally to pull the engine.
The issues I had been struggling with was detonation and poor idle. So I want to make sure that those items are clearly addressed.
I would like to evaluate using different pistons like a more modern hyperuetectic type?
Also determine a good solid lifter cam compatible with my J heads maybe using he same springs if possible. If the cam I have isn’t appropriate for an automatic set up.
Given this how do I communicate to a machine shop that may not be super familiar with a 340 with this crank and internal set up?
I need to keep the cost down as I am so far past my budget already.
The issues I had been struggling with was detonation and poor idle. So I want to make sure that those items are clearly addressed.
I would like to evaluate using different pistons like a more modern hyperuetectic type?
Also determine a good solid lifter cam compatible with my J heads maybe using he same springs if possible. If the cam I have isn’t appropriate for an automatic set up.
Given this how do I communicate to a machine shop that may not be super familiar with a 340 with this crank and internal set up?
I need to keep the cost down as I am so far past my budget already.
The first thing you need to do is physically measure your compression ratio.
If you have a detonation issue I suspect it’s probably not from too much compression.
Ok Ill see if I can figure out the detail's.. I think I need to best calculate this with the engine out.
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Assuming a 0.040 (need to confirm) head gasket and a 10cc piston (I need to confirm) and a 0.03 over bore confirmed. I estimate the CR to be approximately 11:1
4.3 + 0.5 + 0.61 = 5.41 cubic inches
Swept Volume: ~54.5 cubic inches
Total Volume at Bottom Dead Center:
54.5 + 5.41 = 59.91 cubic inches
Compression Ratio:
59.91 ÷ 5.41 ≈ 11.1
I am going back to find a picture I believe I have of the piston number to get a better estimate on piston volume.
I know this is not super accurate but so far it’s telling me the cr is probably not 12:1 but something lower. I don’t know the relationship of static cylinder pressure to cr but 205 psi seems like an issue whereas 11:1:1 does not.
I don’t have the skills knowledge equipment and experience to measure the exact cr. Is this necessary? Shouldn’t the final gasket size and piston be selected to give the shop my target CR?
I want to shoot for 9:1 to 9.3:1 since shitty 91 Octane is all I can practically get here in AZ and iron J heads.
- Chamber Volume: ~4.3 cubic inches
- Gasket Volume: ~0.5 cubic inches
- Piston Dome Volume: ~10 cc ≈ 0.61 cubic inches
4.3 + 0.5 + 0.61 = 5.41 cubic inches
Swept Volume: ~54.5 cubic inches
Total Volume at Bottom Dead Center:
54.5 + 5.41 = 59.91 cubic inches
Compression Ratio:
59.91 ÷ 5.41 ≈ 11.1
I am going back to find a picture I believe I have of the piston number to get a better estimate on piston volume.
I know this is not super accurate but so far it’s telling me the cr is probably not 12:1 but something lower. I don’t know the relationship of static cylinder pressure to cr but 205 psi seems like an issue whereas 11:1:1 does not.
I don’t have the skills knowledge equipment and experience to measure the exact cr. Is this necessary? Shouldn’t the final gasket size and piston be selected to give the shop my target CR?
I want to shoot for 9:1 to 9.3:1 since shitty 91 Octane is all I can practically get here in AZ and iron J heads.
Wallace Racing: Dynamic Compression Ratio Calculator
static is mechanical compression. Dynamic is the swept volume compressed by your mechanical compression ratio. AKA effective stroke.
Entered 10.875:1 compression
3.31 stroke X 4.07 bore
1000' da. with 48* closing timing.
Static compression ratio of 10.875:1.
Effective stroke is 2.92 inches.
Your dynamic compression ratio is 9.71:1 .
Your dynamic cranking pressure is 204.65 PSI.
Your effective boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of 0 PSI is 9.51 :1.
V/P (Volume to Pressure Index) is 187
Thanks @Illahe But I am not sure how to interpret all of this and what your assumptions are. Bottom line if I am running at approximately 9.5:1 or 11:1 @Newbomb Turk has a theory and trying to help me understand that the detonation I am seeing is probably not CR.
Lastly I was running an MSD 6AL and MSD billet and tried a bunch of slow curves with max all in as low as 24°. Still detonated. I am now running a Progression Distributor that I have run countless maps in a similar fashion. All running on 91 which is the best I can get.
Listen to Nb,T. 91 octane is trash for your dynamic compression.., but you can likely get it to run without destroying itself.
What is your valve lash set at? if its not a tight lash grind (.014" lash) you could probably "tighten the lash .002" and bleed off about 5~# of compression. Ask Nb,T.
To many cooks spoil the soup!
I just gave you some insight on where your (psig) cylinder pressure is coming from: Valve closing/mechanical/swept volume.
Thanks. The other issue is that since I got this engine with no information I don’t know what cam is in it. When I set lash I believe I used .020/.020 that may be off from ideal.
.20/.20 may be loose causing 205psig. Who ground the cam? Brand?.
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