Dead #5 Cylinder. Can I keep going...?

[glealey]

1989 Mercuriser 5.7L with alpha I

Took the boat to a new mechanic for some standard maintenance (bellows and impeller). The mechanic came well recommended by a few fellow boaters. Today he showed me that I have zero compression on my #5 cylinder! All others checked out good at about 165 cold. So, my mechanic recommended pulling both heads, having them "mechined" & replaced, adjust carb, and set timming. His estimate is about $1400 (gaskets $170, machine shop $300, labor $900). While I was there he put a camera in through the #5 spark plug hole and showed me around. He said it looked very good (no gouges, dings, etc). This is what led him to think that it's a head gasket or cracked head.
I'm getting to the question... When listening to it running today with the mechanic he said it's obvious to him that it's not firing that one cylinder. However, when I listen to it I find that it sounds exactly the same as it alway has since I've had it (past 10 years). Could it have been running for years with a "dead" cylinder? It's always ran a little rough a low rpm's. More importantly, since the boat is only worth about $3000 now, can I continue to run it without making the repair an expect it to perform the same? It doesn't make since for me to put $1400 in it when it still runs as "good" as it has/does... Can I get another year or two out of her?

 

[glealey]

Re: Dead #5 Cylinder. Can I keep going...?

One more thing,
A colluege of mine (who is not a mechanic) told me that I should consider simply removing the valve cover and seeing if I have a stuck valve at the #5. He thinks that a valve could cause it to read 0 compression. If that's true wouldn't the mechanic have sugested that?
By the way, when I say that it has 0 compression, I mean that the needle on the guage wouldn't even move when cranking. But again, both cylinders beside the #5 read 160-165.

 

[Scott Danforth]

Re: Dead #5 Cylinder. Can I keep going...?

do the compression test yourself. I would also pull the valve cover like your college stated, you may have a bent pushrod.

if you have a bit of mechanical ability, you can do the labor yourself and save the $900

 

[tpenfield]

Re: Dead #5 Cylinder. Can I keep going...?

I have an idea . . . let's go to a different mechanic . . . or better yet do a compression test of your own.

A red flag for me is wanting to remove both heads and mill them in order to fix an unknown problem in #5 cylinder. It could be repairable for a lot less. I would leave the starboard side alone, since you have very even and high numbers.

 

[fmalott]

Re: Dead #5 Cylinder. Can I keep going...?

One more thing,
A colluege of mine (who is not a mechanic) told me that I should consider simply removing the valve cover and seeing if I have a stuck valve at the #5. He thinks that a valve could cause it to read 0 compression. If that's true wouldn't the mechanic have sugested that?
By the way, when I say that it has 0 compression, I mean that the needle on the guage wouldn't even move when cranking. But again, both cylinders beside the #5 read 160-165.

your friend has a very good point, take the valve cover off to see if one of #5 valves are stuck open if they are then yes i would get head rebuilt and while your at it do both, also maybe rings are shot or burnt a hole in piston or as mentioned before the head gasket is blown at that cylinder or the head is cracked what ever the problem is you have to remove heads. as for the mechanic if your not mechanically inclined than spend the money, if your able the do the repaires yourself the save money and do the repaires yourself, machining your heads you wil have to pay $300 regardless who does the repair GOOD LUCK!

 

[glealey]

Re: Dead #5 Cylinder. Can I keep going...?

So, how about my question of running without making the repair? I'm gussing I've been doing so for years now...

 

[Pete104]

Re: Dead #5 Cylinder. Can I keep going...?

Zero compression comes from an opening not a crack.
All the other responses have alot merit & there are other possibilities. Including, that vintage engine was known for cam lobes flattening.

300 for machine shop sounds way low.

Well, you won't make it any worse! I'd say drive it til, well whatever happens.

 

[Ryanlewis2010]

Re: Dead #5 Cylinder. Can I keep going...?

300 is all i payed for head reman, block bore and hone and magnaflux plus core plugs instal

 

[glealey]

Re: Dead #5 Cylinder. Can I keep going...?

Zero compression comes from an opening not a crack.
All the other responses have alot merit & there are other possibilities. Including, that vintage engine was known for cam lobes flattening.

300 for machine shop sounds way low.

Well, you won't make it any worse! I'd say drive it til, well whatever happens.

Was thinking the same thing about the flat zero compression. Without knowing much about compresssion tests, it just seems strange to me that it reads absolutely nothing, not even a jump in the neddle on that one cylinder. Makes me think something is "open", but I'm just not knowledgeable enough in that area to know if that's possible. I worry that the suggested repair of machining the heads isn't really the culpret and I turn a $1400 repair into more and more. Hence the thought to just "ride it out".

 

[fmalott]

Re: Dead #5 Cylinder. Can I keep going...?

Zero compression comes from an opening not a crack.
All the other responses have alot merit & there are other possibilities. Including, that vintage engine was known for cam lobes flattening.

300 for machine shop sounds way low.

Well, you won't make it any worse! I'd say drive it til, well whatever happens.

Cam lobes flattenning would not cause 0 compression there still would be compression beause the worn out cam lobes would not open the valves so valves not open causes compression and yes if the head has a crack it would cause no compression where would the compression go if there is a crack i would not have a motor runnning on a missing cylinder you can fix this problem your self for half that price

 

[Lone Duck]

Re: Dead #5 Cylinder. Can I keep going...?

Pull the head and look. If you don't want to bother. pack a spare outboard.

 

[riptorn]

Re: Dead #5 Cylinder. Can I keep going...?

Pull the rocker cover off that side and check the 2 rockers on num.5. If it looks ok start her up and check er out. No cost if it is something simple you can fix your self. Dead zero reading seems sketchy unless you have a hole in the piston the size of a dime like Pete104 said.

 

[picklenjim]

Re: Dead #5 Cylinder. Can I keep going...?

Sounds to me like you have a bent or severly burned exhaust valve which is leaving an opening during compression. If it were the intake valve it would be back firing like hell out the carb. A blown head gasket would still show some compression. A crack would still show compression. Worn rings would still show compression. A hole burned in the piston would create extreme blow by and you would have high crankcase pressure and smoke coming out of any breather opening besides he looked inside with the scope and would have seen a hole in the piston. I'm not so sure they can even see the valves with a scope going in through the spark plug hole. IMO it has to be the exhaust valve bent and hanging up in the guide or a piece of it is burned away. Both are common. Freshen up both heads. $1400 sounds about right to pull, work up and replace both heads on a V8.

 

[picklenjim]

Re: Dead #5 Cylinder. Can I keep going...?

300 is all i payed for head reman, block bore and hone and magnaflux plus core plugs instal

On what a V-2 Briggs & Stratten ? All I can figure is you must own the machine shop and be doing the work yourself.

 

[tpenfield]

Re: Dead #5 Cylinder. Can I keep going...?

So, how about my question of running without making the repair? I'm gussing I've been doing so for years now...

Well, that's the thing . . . I think you would have noticed. So, are you sure that there is zero compression in that cylinder? Did you see it for yourself. One thing you could do is take the spark plug wire off #5 and ground it to the block somewhere, then run the engine. See if you notice a difference then.

 

[Bondo]

Re: Dead #5 Cylinder. Can I keep going...?

So, how about my question of running without making the repair? I'm gussing I've been doing so for years now...

Ayuh,.... Sure, Go ahead....




Just don't go far from the ramp, 'n bring paddles....

 

[04fxdwgi]

Re: Dead #5 Cylinder. Can I keep going...?

Pull the valve covers off and rotate the engine so #5 is at TDC. Check that both pushrods are still snug. You may find you have a valve stuck in the open position, indicated by a pushrod being very loose, caused by the valve not closing completely. Seen it many times......... Especially on SB Chevy engines. Have also seen the pushrods pierce rockerarms too, causing the rocker arm to jam in the open position.

If this is the case, squirt some mystery oil on the valve stems, let it sit for a bit. Remove the rocker of the effected valve and give it a couple of thumps with a hammer, not too much, and it may break the valve stem loose in the guide. This has worked well for me over the years when getting used engines from the "bone yard" that has been sitting for a while, especially uncovered.

Sounds crude, but it works sometimes. If nothing else, it'll show you what needs to be done to get it right.

 

[Ryanlewis2010]

Re: Dead #5 Cylinder. Can I keep going...?

On what a V-2 Briggs & Stratten ? All I can figure is you must own the machine shop and be doing the work yourself.

Nope. now mind you it was only an inline but it was a 140 head so if he is only missing the starboard side, he only needs to machine one head. which shouldn't be to much. Also if i owned the machine shop i would be way to busy to be on here i love rebuilding motors i do however get discounts on the parts but not labor

Edit and apart from being able to to the work your self all you need to do is unbolt 8 bolts and stick it in a box and take it to a machine shop for examination. if they aren't low life's they should tell you what you need and if you even need to reman the head

 

[Silvertip]

Re: Dead #5 Cylinder. Can I keep going...?

A valve that is stuck open or a bent push rod causes lifter noise since the clearances are way outside what the hydraulic lifter can compensate for. Auto stores that rent tools will rent a compression gauge. Do it and actually prove to yourself there is a compression problem. Remove the valve cover and rotate the engine while observing the rockers. Using a dial indicator (or even a ruler), check valve lift on that cylinder and compare to another pair of valves. If they are the same, you likely have a leaky valve. If not, then a flat cam or worn valve train components are suspect. Then remove, inspect and rebuild or replace the head. Pushrods can be rolled on a pane of glass to see if they are bent.

 

[achris]

Re: Dead #5 Cylinder. Can I keep going...?

Did you all miss this????

.... All others checked out good at about 165 cold. ....

Compression readings are only valid if done with the engine warm, the throttle at full open and all spark plugs removed....

Run the engine and do the test yourself....

If you still have a problem, THEN start looking for it...

Chris........