FOUND SOMETHING! CYLINDER NOT FIRING!

[rodbolt]

Re: FOUND SOMETHING! CYLINDER NOT FIRING!

dont use the indian rope trick it can cause more problems than its worth. <br /> a poor mans leakdown is to remove both rockers for that cyl. inject compressed compressed air at about 100 psi. listen for air leaks at the exhaust pipe and the carb. if no major leaks are found release the air and rotate the pison to tdc. reapply the air. be aware that if its not locked at tdc by the crank or flywheel it will rotate to the bdc position.rapidly. if the valves seal and you can keep air in the cyl the springs can be removed at the bdc position. but ususlly you can see a broken spring by measuring the installed spring height and comparing it to the service manual or another valve spring.changing valve stem seals with this method was very common in the 70's and 80's when I did autos for a living. most tool rental places will rent the tool to use the stud to remove the spring. if not the are usually less than 20 dollars.

 

[Trent]

Re: FOUND SOMETHING! CYLINDER NOT FIRING!

Id love to hear what problems it causes rodbolt? Been doing it for over 25 years... Always love to learn.<br /><br />I also agree with rodbolt... but ususlly you can see a broken spring by measuring the installed spring height and comparing it to the service manual or another valve spring.

 

[rbezdon]

Re: FOUND SOMETHING! CYLINDER NOT FIRING!

I guess I wasnt so far off with the compressed ait thing but shoving "stuff" like a rope (how big?? in there and never knowing what got left behind bothers me a bit but I might try it if I were desperate. Problem is most of us DIY guys dont have good air tools/facilities. I dont. Its easier for me to just pull of the head.

 

[rodbolt]

Re: FOUND SOMETHING! CYLINDER NOT FIRING!

trent<br /> cant help what you have done for years.<br /> the past 30 years you would not believe how many "rope" tricks I have had to correct. one I had to pull the head to retrieve the rope. saw a friend try it to stop piston rotation on a 2 stroke. clipped a piece off and ended up locking the motor and damaged the rings. they could not wait till I got off work and stuffed it full of parachute cord. I usually dont recommend putting anything in a cyl that does not normally belong there. I also always reccomend before shotgunning a trouble shoot to test the basics, even if ya just tested them yesterday. I saw a piece of wire from a wire brush tear a piston to pieces in 2 hours. usually if ya think about how and why each part of the engine works and how it works with the next part its fairly simple. when it comes to the reciprocating assy you can think of it as multiple engines sharing common parts such as manifold castings and a crank. each cyl must be sealed from the other yet all must perform close to identical. if one intake cam has a .450 lift all should have. same as exhaust. if one intake spring has a 1.5" installed height so will all the others. thats why ya shim the springs to fit. after shimming the spring open pressure with the shim should be checked. the head can be machined as needed. usually a broken spring can be found with a vacum gauge. you will see a steady downward flick of the needle . a vacum gauge if ya know how to read it will tell ya almost anything you wish to know about the sealing capeability of the engine. you can find all sorts of things with it. if I had 4 tools in the box it would be my leakdown tester, my vacume gauge , my Kv tester and my DVM.same as the computer diagnostics. nine times out of ten the engine runs poorly or not at all yet no codes will be set and the puter will tell you all is good. but by watching things like the map sensor, the fuel pulse width and such you can get an idea of where to look. always remember that colum of air the intake valve just let in is about 10 miles high. if all valve are equal the same amount of air will move for each. it also has to stop and start. thats why sometimes the CFM fourmula for a specific CID is not quite right. otherwise the 1050 dominator we ran on our 355 chevy would have flooded it. we relied on the inertia of that 10 mile high colum of air to assist in cyl filling. for basics its always suck,squeeze,bang and blow, everything on the motor helps time it.

 

[Peter J Fraser]

Re: FOUND SOMETHING! CYLINDER NOT FIRING!

What about the possibilty of a lifter having a faulty check valve and pumping up, causing a valve to hold off the seat very slightly.<br />This could dump the compression out very quickly indeed and create the symptoms.<br />If an intake lifter then it would blow back into the inlet manifold and contaminate the air charge for the other cylinders on that sequence.<br /><br />Peter

 

[Scaaty]

Re: FOUND SOMETHING! CYLINDER NOT FIRING!

I've changed valve seals on Harley's with just compressed air, and thats pushing down on the valve. Just like rodbolt says though...TDC and lock the motor. Get a couple springs first, and just change them. And I made a fitting for air out of a old spark plug. Busted the porcelain out, and brazed in a QD. You can probably get away with a portable air tank, just have everything ready before you pressurize the cylinder...it will leakdown. Best to test first if you go that route.

 

[DJ]

Re: FOUND SOMETHING! CYLINDER NOT FIRING!

freebee,<br /><br />Without dismantling anything, you can hook up a vacuum guage to a port under the carb. That will tell you if you have cam or valve problems.<br /><br />You should have a steady needle at around 16-18 inches.

 

[Limited-Time]

Re: FOUND SOMETHING! CYLINDER NOT FIRING!

FBT, <br />This link should help interpret the vac. readings. Can't remember if I gave it to ya before.<br /> http://users.bigpond.net.au/ergoff/vac1.htm

 

[FreeBeeTony]

Re: FOUND SOMETHING! CYLINDER NOT FIRING!

Thanks DJ an LT........<br /><br />I did do the vaccum test and it seemed normal.<br /><br />However, this cylinder has compression at idle, the problem doesn't appear until higher RPM's, so would the vaccum test still show a problem at idle?<br /><br />Yes LT.....think you may have forwarded that link before.......but thanks. Never new how powerful a vaccum gauge really was!<br /><br />Maybe I just have a hung up lifter?<br /><br />Will keep you guys posted on tonight's findings.....only get about an hout or so to work on it at night.......boat is in the water.<br /><br />Will inspect condition of valve springs and push rods tonight.

 

[DJ]

Re: FOUND SOMETHING! CYLINDER NOT FIRING!

However, this cylinder has compression at idle, the problem doesn't appear until higher RPM's, so would the vaccum test still show a problem at idle?<br /><br />

Freebee, yes, do it at the speed you notice the problem.<br /><br />As I recall, that engine has "side covers" for the lifters/cam. If you can get to those covers, looking inside will speak volumes. That may be an easy "looksee" for your cam and lifter health.

 

[ottawamerc]

Re: FOUND SOMETHING! CYLINDER NOT FIRING!

I just check out the vac. gauge site. Thats a great reference. well done!<br /><br />Scott

 

[FreeBeeTony]

Re: FOUND SOMETHING! CYLINDER NOT FIRING!

DJ.......you are thinking of my IL6, this is a V8.

 

[rbezdon]

Re: FOUND SOMETHING! CYLINDER NOT FIRING!

FBT, I think Dj missed something as he is a vet and there are definately no side covers on a SBC 350. The only access to lifters is through the intake valley. But you can definately see the lift in the rockers if you just pull the rocker covers and this will let you know if it a lifter and or cam lobe.

 

[FreeBeeTony]

Re: FOUND SOMETHING! CYLINDER NOT FIRING!

Pulled the valve cover tonight for the inspection.....<br /><br />1) cranked engine to check cam lift: seemed ok, measured as best I could, all intakes were the same and all exhausts were the same<br /><br />2) pulled rocker arms on #3: checked rocker arms and push rods, both looked ok<br /><br />3) inspected valve springs as best I could without removing them: could not see any damage, also pushed down on them with a screwdriver and they seemed to have the same resistance as the springs on #1 (removed rocker arms on #1 also)<br /><br />4) I then poured marvel mystery oil down the pushrods on #3 in case a lifter is hanging up<br /><br />5) looking through an opening in between the push rods I could see the lifters, could see the retainers indicating it has roller lifters. any way to check the lifters without removing them?<br /><br />6) can I get the valve springs at any auto parts store? are the intake and exhaust springs the same?<br /><br />7) if I use air to keep the valves seated while I replace the springs, would a portable air tank be good enough? there isn't any electric power where the boat is docked to use a compressor

 

[steve n carol]

Re: FOUND SOMETHING! CYLINDER NOT FIRING!

Tony, when you are ready to remove any valve springs, if that is waht you need to do, stuff rags around the valve/spring in question. this way if the keepers fall, you might not loose one down into the lifter valley/crankcase...sl<br /><br />yes, to the Question on the portable air tank....BUT, the real question is....<br /><br />How well do your rings and valves seal?<br /><br />As stated above, 'you will get some leakdown'...you need to continiously supply compressed air, as "the rodbolt" said...'bout a 100 pounds...sl

 

[Buttanic]

Re: FOUND SOMETHING! CYLINDER NOT FIRING!

If your engine has exhaust valve rotators then the exhaust springs are shorter than the intake springs. If it doesn't have rotators the exhaust springs are the same as the intake. You can get them at NAPA.<br /><br />exhaust spring-AE Clevite Engine Parts 2121198 1.610 installed height <br /><br />intake spring- AE Clevite Engine Parts 2121150 1.701 installed height

 

[FreeBeeTony]

Re: FOUND SOMETHING! CYLINDER NOT FIRING!

Thanks Buttanic........the exhaust valves do have rotators.<br /><br />Figure I might as well replace them while I have it apart.<br /><br />The manual calls out for the same spring in both intake and exhaust? 24-48347 Lavender stripe?

 

[Buttanic]

Re: FOUND SOMETHING! CYLINDER NOT FIRING!

"Figure I might as well replace them while I have it apart.<br /><br />The manual calls out for the same spring in both intake and exhaust? 24-48347 Lavender stripe?"<br /><br />I noticed that the Mercruiser parts break down doesn't show different springs for the intake and exhaust. Don't know what the deal is. But from about 1973 on all Chevy small blocks with rotators use shorter and slightly smaller diameter springs on the exhaust. I guess some manuals are generic and expect the engine builder to know or measure the old spring.

 

[rbezdon]

Re: FOUND SOMETHING! CYLINDER NOT FIRING!

Also, Tony doesnt have the original engine, it is a newer year than the boat if I remember correctly, only maybe 4 years old or so. Is the manual for the original setup in the boat or the rebuilt motor??<br /><br />And Tony, watch out for the keepers as warned above. If you haven't pulled valves before it may be different from what you expect. Loose one of those things down the engine somewhere and you'll have to pull the whole thing out to get it out. These Pros here have great experience!! Bet they have seen us DIY guys do all kinds of stupid human tricks trying to do this stuff without good advice.

 

[FreeBeeTony]

Re: FOUND SOMETHING! CYLINDER NOT FIRING!

According to the s/n the engine was a '92. I believe it was replaced with a long block in '01.<br /><br />So Buttanic, the difference would be the diameter and height of the spring to compensate for the rotators?