-----Original Message-----
From: owner-dakota-truck@bent.twistedbits.net
[mailto:owner-dakota-truck@bent.twistedbits.net] On Behalf Of Terrible Tom
Sent: Wednesday, January 31, 2007 9:39 PM
To: dakota-truck-moderator@bent.twistedbits.net
Subject: Re: DML: cyl 1 and 7 don't fire
Terrible Tom wrote:
>
> Jamie Calder wrote:
>
>> A while ago I posted a problem I had with my '93 318 where cyl 1 and
>> 7 don't
>> fire. A compression test shows there no compression at all in those
>> 2 cylinders. Before I take the valve cover off for further
>> inspections, would anyone like to speculate? Why those 2 cylinders
>> at the same? Are those 2 always in the same position? What would
>> cause 2 to go at once? What would be the best case scenario? Rockers
>> or pushrods, right?
>>
>> Thanks,
>> James
>>
>>
>
> 1-8-4-3-6-5-7-2 - is the firing order. The number 1 and number 7 are
> the front and rear two on the drivers side bank... Why the two are not
> getting compression, is a little odd.
>
> You either have a situation where the timing is off, and the piston is
> hitting TDC while you have a valve open, you have burnt/broken valves,
> or you have damaged pistons.
>
> Odds are - if the timing has not been fussed with, and the chain in
> intact, you have bad valves. I could see if you had no compression
> between two common cyls, (indicating a hole on the block or head)...
> but two opposites? Its not impossible to have fubard pistons... but
> it would take some serious destructive force to take out two of em.
>
> Why do I not suggest rings? Because even with bad rings, you should
> still have SOME compression, be it very low. If you have ZERO
> compression, I'm suspecting valves.
>
Going to add some more info here. As you mentioned valve train, you could
have a pushrod issue, however if the rods were bent, it would cause the
valves to open less, and you would hear clatter. You would not normally see
zero compression with bent rods.
Also, try this... squirt some clean engine oil into the spark plug holes
for 1 and 7... not a whole lot... half a teaspoon or so... and see if that
bumps up compression at all. If it does - you know its a piston ring
problem. If it doesn't you are back to either valves, holes in something,
or timing.
-- ------------------------------------------------------------ Get a freaking rose tattoo and deal with it... ------------------------------------------------------------ three busted-ass daks, a gas hog, and a rollerskate http://members.aol.com/silvereightynine/ AIM & Yahoo: SilverEightynine ------------------------------------------------------------Here's an update...
I removed the valve cover and cylinder 1 and 7 intake rockers were completely broken off! Now these are the stock stamped rockers being driven by a .512 lift cam and held back by stiff RT springs. Perhaps these rockers simply couldn't can the pressure. Any other ideas why these would fail? Also, since these valves are always closed, shouldn't I have seen full compression on those two cylinders? Or is zero compression normal for broken rockers? Or can a stuck valve cause it to burn? However there was no fuel entering the cylinder with the intake valve stuck closed, right?
I have already have a set of roller rockers on hand that I was going to use for my 408 but not sure if I should install them and call it good or completely remove the head (lot more work...).
I guess I'll try the Compressed Air In The Spark Plug Hole trick too.
Any more suggestions are greatly appreciated!
James
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