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My 340 is spitting & burning oil

73CDNRallye

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I'm looking for some advice on my 340.

It's blowing oil out the breathers and the dipstick. And not just a little, more like a quart every 100 miles (there was a pool on top of the intake after an hour drive yesterday). And it's burning oil under load and blowing smoke when you lift off.

I think most of it is due the rings stuck from sitting, as this seems excessive for just ring wear. The motor had sat for ~7 years until this winter.

I've already soaked the drivers side cylinders with Seafoam spray (since I was told #5 was low in compression), and added some worn ring additive to try and control it.

I think I have two options:
  1. Get a shop open up the current 340, see what's going on, and make a recco - which probably means a engine rebuild
  2. OR finish my stroker - I have a shortblock built, but it will need heads & valve train ++
Cash flow isn't the greatest at the moment, so I'm wondering what to do...
 
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moparleo

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Heads are the key expense with either build.
You could sell the 340 to help fund your stroker.
Pricing will be the problem not knowing the actual internal condition of the cylinders.
 

Steve340

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Get someone to access what is wrong with the 340 and decide what to do from there.
If you do decide to sell it the buyer knows what he is getting.
 

73CDNRallye

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MoparMoMoney

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Sounds like a head issue to me. Maybe stuck valve. Intake issue as well maybe blocked? That’s a lot of oil use.
 

Xcudame

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One of my favorite go to tools for a running engine is a vacuum gauge. It can tell you a lot.
vacumm-reading-1.png
 

cuda joe

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keep the 340 if it;s numbers matching . thats a real good chart xcuda
 

Mike73Dodge

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First, Thanks XCUDAME for the chart. I went and found it on the internet with some added information.
Question for anyone who has used vacuum gauge to tune of diagnose problems.
I have a 340 Block, Stroked and bored to about a 416. Comp cams Hyd roller cam, Edelbrock RPM heads, Milodon oil pump and so on.
The vacuum chart show a normal engine running with a steady 17 to 21 gauge pressure. Mine is not steady at all running at idle. Is that normal for a modified motor?
 

Steve340

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It should be "relatively" steady. The wilder the cam the more messed up the vacuum signal in the inlet gets.
That chart is for standard camshafts your vacuum will probably be a lot lower.
What readings do you get? And is your gauge damped?
 

Xcudame

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Here is a picture of my 70 Challenger's vacuum at idle taken about 15 minutes ago. It has the factory 383/440 HP camshaft and a little over 250,000 miles! A little low, but nice and steady.

Showing a picture of your vacuum gage would help a lot!

IMG_20231029_132046273.jpg
 

hdwrench

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if i was in your situation i would do a leak down test . i have a leak down tester , not expensive at harbor freight. it puts controlled air pressure into a cylinder via spark plug hole . has a gauge that measures leakage. where there air leaks from is indicating what is bad . hardest part is both valves have to be closed , you can rotate engine till valves close or remove the rockers and they will all be closed . compare leakages across all cylinders….a ring or piston damage leaks at breather, intake valve out carb , ext valve leaks out exhaust
 
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Mike73Dodge

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Just got some numbers from my engine. Ran engine for a few minutes, not fully up to temp.
850 to 900 rpm 5 to 15 fast fluctuating
1000 rpm 10 to 12 fairly steady
1200 rpm 13.5 very steady
1500 rpm 15.0 very steady
 

Challenger RTA

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Mike73Dodge Just a suggestion:
Any time you see a rapidly bouncing gauge the first place to look is for a leaking intake valve for whatever reason be it the valve or spring.
Also, cams with a lot of overlap make the gauge bounce as well as read low.
You can remove the bouncing by putting a small orifice in the gauge line to make it more steady to see what the actual reading is.
Normal, What is?
This reading between 17 and 22 inches of Hg is normal. Remember that this figure is optimum for engines running at sea level with factory cams.

Readings may be a little bit lower at higher elevations. The reading should be around one inch lower for every 1,000 feet above sea level. Additionally, for cams with greater aggression, you should anticipate lower readings.
 
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Xcudame

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A leak down test will probably point you towards the problem at this point. Looking at the vacuum gage chart, it points to worn valve guides which will cause a leak between the valves and seats.
 
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I had the same sort of problem. Turned out the head gasket was blown at the top of one cylinder and all the compression was going into the lifter valley.
 

moparleo

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If you still haven't decided what to do. Do the leak down test first.
If the problem is in the heads. That is what you need to do.
If it is in the rings, rebuild of engine is next.
Then you decide what to do $$ in heads for the Stroker or $$$ for an engine rebuild.
 
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