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Discussion Starter #1 (Edited)
I'm having trouble finding out what is normal psi reading for compression check on the ol 400 B block. showing 110-120 on 7 but only 30 on 1 , argh :nono
 

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well with one more than 10% out it probably doesn't matter what normal is.

Sorry about that, hopefully it's just a bad valve or a gasket issue.
 

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I went ahead and looked online, looks like your engine should be around 8:1

That puts the PSI around 117. So looks like your other cylinders are in the ballpark.
 

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OP may be trying to decide if both heads need to come off; the 117 is good news.
... Which cyl is bad, hope it's not #7 !
 

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I see, I read it as 7 cylinders tested good, but one cylinder did not.

You could very well be right. Let's hope it's just the one.

Ron
 

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I see, I read it as 7 cylinders tested good, but one cylinder did not.

You could very well be right. Let's hope it's just the one.

Ron
Your right, 7 cyls all tested good, only 1 bad; but OP did not mention "which" cyl is bad (cyl #7 is the one cyl always at risk of "crossfire", and if failed warrants extra attn).
 

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Key,

Learned something new, I knew what crossfire was, just didn't realize the damage it could cause.

Here is a tech bulletin describing the issue. Just in case I am not the only one uninformed.

http://www.jasperengines.com/pdf/SparkPlugCross-FireTB.pdf
Shmut, my old puter won't hook up to the link; glad you probably found someone who could word it better than me (I didn't think the seriousness/consequences was getting thru).
... GOOD public service cribbs!!
 

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Discussion Starter #9
whats OP? I don't think cross fire is the issue unless it happened earlier in life. everything checks out. Its the number 1 cylinder only getting about 30psi. I haven't done the oil test yet. also i didn't do it with the engine warm or with all the plugs out. I knew about the 8:1 but don't know how to figure the 117psi. getting over my head. I sure appreciate all the interest! keep it coming. thanks
 

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Well, glad it's #1 , but the bad news is the head is probably going to have to come off. If the oil test increases the compression then the engine is coming out.... Lets hope it's not that!

Unless someone can think of something else that is. You could pull the valve cover off and see of a valve has dropped I suppose.

OP is the Original Poster.
 

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Might be time to put air to that cyl, and "listen" at carb, exhaust, and oil fill cap (tie throttle open, and remove oil fill cap BEFORE putting air to cyl).

Shmut, link still won't load
 

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Discussion Starter #12
at 100k if the heads come off engine needs redone anyway probably huh. whats the chance of having good cylinders and just need honing and re-ring and valve job? wishful thinking? if it has to come out then might as well do the tranny too. heck, might as well just stroke it, where does it all end? haha
 

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Discussion Starter #13
ok, so, im guessing that if no air sound through the oil cap means good rings maybe, and air throught the exhaust or carb could mean intake or exhaust valve. right?
 

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Sorry, not to jack,

cribbs: saw the link, good, but they're a bit too kind (can also destroy/loosen main caps in their registers, and cyl "bores" can split or stretch/deform).

... They were kinda foggy about the two critical cyls involved, the "advanced 90* cyl (LA #7 ), and the wire that can fire it way too early (LA #5 ), all V8s have them, they are always (rule of thumb)---

--- "the two cyls that "are physically beside each other in the block, AND follow each other in the firing order"
(if plug wires are routed normal and "pretty looking", they would run parallel because they are physically beside each other, both at the block and the cap)

... IMO, for LA: if wire set has 90* boots at the cap, #7 wire should be different (straight or angled boot) and longer, so it's up and away from #5 .
 

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ok, so, im guessing that if no air sound through the oil cap means good rings maybe, and air throught the exhaust or carb could mean intake or exhaust valve. right?
Yup; although a bad valve will lessen pressure on the rings, and could "possibly" hide bad rings.

... With the 400s "slow cyl speeds" due to long ish rods (high rod ratio), bores a likely good.

#1 chamber is the last one to get coolant, and likely runs the hottest (wild guess, lol, exhaust valve); but you will know soon
 

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Discussion Starter #16
yes i will mr key, and thanks for the optimistic smile. come on 60 degrees. all the wood in the forest doesn't stop that concrete from being cold ha
 

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Ya, springs around the corner; hopefully no going underneath; if the air shows a valve, do as cribbs74 said and pull the cover (could be stuck valve, or broken spring, who knows).
... It was never mentioned how it ran etc; spitting out carb, exhaust, blowby pulses etc
 

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Discussion Starter #18
its just rough at low rpms, not much power, lots of blowby from valve cover breather with smoke too. probably needs everything! gotta get it in.
 

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Discussion Starter #19
finally did a new compression test, still only 30 on no. 1 cylinder. drove it up on ramps (just the driver side so the cylinder would be more plum), put some oil in the cylinder and did another test, this time getting a little over 60. oops.
Also i drained the oil and filled the cylinder full of tranny fluid (hoping for the stuck ring syndrome) for about 5 hours. not much ran out of the drain plug, but some did). then refilled with 10w40, ran it without plug in no.1 cylinder for a bit to blow most of the tranny fluid out, then replaced the plug. when i fired it up it blew smoke out of the left side for a while til it got good and warm and finally cleared up. it seems to sound better but im sure it just likes the new oil. haven't re tested it yet but i'm guessing it will be about 30 haha.
the good news is that after adjusting the ol 727 tranny it is running and shifting (i hate to say it) perfectly!
 

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Bump: hows the 400?
 
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