Leak Down Findings

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Mopower71

Mopower71

Speed Demon
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Well...... Good news? and bad news!
Good news: I know now why the car only runs 12.6's

Bad News: Car won't be going to Mopars at the Valley.

I did the compression test earlier this year and they were 220 +/- 3psi over all 8 cylinders.
I did the leak down today :cry:
1-20%
2-16%
3-62%
4-22%
5-15%
6-18%
7-22%
8-32%
On all of them I could hear it leaking into the crankcase.
#3,5,6 and 8 are also leaking thru the intake.
#3 had the most leakage thru the crankcase, and #3 and 8 were bad thru the intake.
I did not climb under the car to listen in the exhaust.
So that's where I'm at now. I knew what I would find before I started, but was hoping I was wrong.
Time to sit down and think this over,and decide what to do next.
 
:dontknow: Guess I'll find out when I tear it down.
First thing is I don't think the rings ever fully seated.
Teardown will tell
 
I'm assumeing that the 340 is in the car now? If so it would cost less cause you wouldn't have to buy the big block stuff. But If you have that stuff allready, then there is no difference. Generally speaking. 440's cost more for parts if I remember rite.
340 is lighter and you might be able to make the same power out of it.

Just some thoughts.....Good luck.
 
halfaed said:
I'm assumeing that the 340 is in the car now? If so it would cost less cause you wouldn't have to buy the big block stuff. But If you have that stuff allready, then there is no difference. Generally speaking. 440's cost more for parts if I remember rite.
340 is lighter and you might be able to make the same power out of it.

Just some thoughts.....Good luck.
Click to expand...
Yup, the 340 is in it now, But I have all the stuff to install the 440,it's already been in the car. It's an easy swap.
Both engines are going to need to be torn down and gone thru.
:-k :dontknow:
 
that is a hard decision but if i where in your place i would go for the power of the bigblock since you got all the stuff to install it!
 
I would have to agree about the 440, the cost difference will be minimal to rebuild it. What would you do with the 340 then?,,,,,And what heads do you have on the 340? I've raced the car once and I'm already looking to upgrade:)
 
I did a leakdown on the 440 today. Cold and has been sitting for over a year now. I did pull the rocker shaft off just to make sure the hyd weren't olding the valves open.
Side note: After being run hard for 15 years, I was totally blown away hat how spotless the top end is. No gunk, no nothing. just a small amount of oil residue.
1- 12%
2- 15%
3- 16%
4- 40%
5- 44%
6- 33%
7- 18%
8- 28%

#4,5 and 6 all have leaking exhaust valves. I did tap on them with a rubber mallet, but it didn't help.
#8 cylinder was just leaking past the rings into the crankcase.
Well There it is.
:walk:
 
halfaed said:
I would have to agree about the 440, the cost difference will be minimal to rebuild it. What would you do with the 340 then?,,,,,And what heads do you have on the 340? I've raced the car once and I'm already looking to upgrade:)
Click to expand...
You're hooked
:grin:
The 340 would eventually get rebuilt also.
I'm trying to do one at a time.
One of the engines will eventually end up back in the Dart.
The 340 has ported X heads on it now.
 
Before you take that 340 apart, think. Most of the leakage seemed to be coming from the intake valves. Sounds like a valve grind is needed. Almost every motor will have some noise coming from the crankcase during a leakdown test. That's where most of the leakage is at, the rings. If it was mine........I'd pull the heads and get them checked and maybe a touchup on the valve grind will put you back in business. You probably won't notice much of a difference in power in a cylinder that leaks 20% versus 5%. I've seen engines that leaked 25% that were rebuilt professionally and only pickec up a tenth or two. A lot of money and time for a little gain. Maybe a $200 valve job will be a better bang for the buck.
 
What was the ring gap set to in the 340? If it has KB Hyper pistons then the ring gap may be large. Maybe pull the piston from the worst hole and take a look at the rings? You may just need to hone the cylinders and slap a new set of rings on. That and a valve job on the heads.
 
Well Norm, at least now you know. I agree some crankcase leakage is normal, especially on an engine that has not fully seated yet..However, you have valve issues. If it were me, I would continue with the small block until it goes right. Pull the heads, see what the pistons look like. Are they bent, or just poor seat work? They obviously need help, and existing is always cheaper than a swap. Plus, the 440 may be claen, but doesnt sound much better. I'd ge the heads fixed properly, take the opportunity to address any other engine problems whiel it's apart. Then do the 440 over while you beat the tar out of the 340..lol.
 
With Number 3 leaking so bad into the crankcase, I figure that's where most of the smoke is coming from.
The 340 is going to be interesting finding headgasket/o-rings for, I would realy rather not have to take it to a macine shop. There's no money in the budget for that.
 
It already has to go to the shop..either engine really, so just put things down until the $$ is there. I forgot about the Oringing...It shouldnt be hard to just take the p/n from what comes out, and order new ones. I wouldnt be concerned with the smoke just yet..A weak cylinder will smoke, and all those non-sealing valves are making weak cylinders. They cant be fixed without some machining.
 
If I can chase down a few tools that I need, I would much prefer to do the valve job myself. I think I know where some of the equipment ended up at.
 
I pulled one of the heads off the 340.
The cylinders are as smooth as glass. So that explains the leakage past the rings.
At one time the engine must have spit out 2 of the push rods, one on each side, as there is marks on the roller rockers. They appear to be fine, as the damage is not to close to the adjuster.
Next I need to pull the valves out of the head and see what's up there. It appears the valves have been replaced with some LARGER ones, but it looks like the ports are untouched.
Another thing I noticed when I had the carb off but the intake still on is how much of the head I could see looking down the plenum. Boy does that need to be fixed. There is at least an 1/8" lip I can see. I'll have to get out the grinder and match these ports.to the intake.
 
See...Progress without money ...yet. YOu can alway scuff the bores (ball hone) to break the glaze, then toss the thing back together with fixed heads..That step on the port roof hurts a bit...And the seats were never cut for the larger valves?
 
moper said:
See...Progress without money ...yet. YOu can alway scuff the bores (ball hone) to break the glaze, then toss the thing back together with fixed heads..That step on the port roof hurts a bit...And the seats were never cut for the larger valves?
Click to expand...
I'll know more about the heads when I pull the valves out. The seats look like they were cut for the valves.
I'll have to look closely at the rings and also check the end gaps to see if they will work.
I have to do a bit of searching and find out what pistons these are.
The number stamped on the top is 3690825 but I don't know what make.
They also have 340 and .030 stamped in the top. The good thing is whoever put it together stamped the cylinder number on the top of the piston, so I won't get them crossed up.
The heads # is
2531894-D
08058
AAWJ 340
 
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