Valve problem, what to do?

F

frankn88

New Member
Jun 15, 2009
95
Eastern Shore, MD
Boat Info
270 Sundancer 1994
Engines
5.7L Merc w/ Bravo II
Boat will not go above 3000-3200 under load. Tried all the easy things, and finally had someone look at it. They did a compression check and all valves are 140-160 except one that is "sometimes up to a 100, sometimes only 25" (This is from a message they left me. He says it's probably a bent valve or broken spring or something and they want to pull the heads and "probably need a valve job". Engine's got about 490 hours on it. Had a bent valve a couple years ago, don't know if this is the same cylinder or not. So the questions are: if it's a bent valve or broken spring, do I really need a valve job; and if I really need a valve job, is it time to just get a new long block; and if so, where should I get it? Oh, and anything else I haven't thought of? Thanks!
 
If you really want to know , do a compression test yourself , if you find the same , pull the heads , look at the top of the pistons , if they look OK , take the heads to a machine shop. Jasper is a good place to find a reman engine.
 
a bent valve would be a consistant mechanical defect...compression would not vary
a broken spring could cause your issue and can be repaired without pulling the head.
if I were you I would do the comp test myself of get a second opinion from someone else QUALIFIED
too much money to guess at it IMO
 
Well I called him back and got some more info. #5 is the problem child. He said the compression # could vary if it was bent because sometimes it might seat pretty well and other times it might not seat as well and get some blow by. He said it would be about $320 to pull the head (port side) and another $320 to reinstall it (he said it's about 4 hours of work both ways - does that sound right?). He's going to get prices from a machine shop on the valve job, and also prices on manifolds, risers, and a long block and send it all to me so I'll have some heavy thinking to do...
I had a bent push rod a couple years ago (unfortunately I do not know which cylinder it was), and had the push rod replaced and went on my merry way. Could it be another bent push rod? (I know, I know, do it yourself and check for yourself...) I've had the boat for 4 1/2 years and never replaced manifolds or risers. So, depending on the numbers he comes back with, I see a few options: Just replace the valve (assuming it's just a bent valve), and put it back in the water and run it till it dies then worry about a new engine (I'm sure many people cringe at this option, it really doesn't bother me that much, I enjoy living on the edge! ;o) or do a valve job, manifold and risers, or get a new long block (and I guess still manifold and risers). I could probably do the valve by myself, and manifolds and risers, but I am definitely not set up to replace an engine.
Thoughts? Comments? Rocks? I mean with almost 500 hours on the engine, how much more can I reasonably expect out of this thing regardless of what I do? Thanks again for your helpful insights!
 
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again...bent stuff doesn't register as bad "sometimes"
could be a dropped valve seat or a sticky valve also...these are the only things I have ever seen cause erratic
compression readings....a cylinder leak down test would be my next step to see where the air is really going.
 
I would do all the pre dismantelling test suggested herein first. Leak down for sure! Based on what you write I believe you may need to pull that head and it sounds like your mechanic is on the right track. Also, why are you bending rods and valves. There is something there that must be identified. Unfortunately you need the pull that head to verify. On the good side, once you have that head, or the heads, off you can see the internal condition of your engine.

Regarding considering a long block, I don't think you are there yet. When, and if, you pull the heads you will have a visual that will help you make that decision. It sounds like a head job is in order and a clear reason for the bent valve, if you have a bent valev. Valves don't bend without some type of impact or water in the cylinder. You could have a cracked head, bad head gasket, or failing risers.

Start with the basics like; check for water in oil, a leak down test then open the rocker covers to see if you have a bad spring. Then... pull heads. Then...see if you need an overhaul or long block. One less costly step at a time.

Good luck!!! Hopefully its just a broken spring! :smt001
 
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frankn88 said:
Thoughts? Comments? Rocks? I mean with almost 500 hours on the engine, how much more can I reasonably expect out of this thing regardless of what I do? Thanks again for your helpful insights!
Click to expand...

I wouldn't be boating if I had to replace engines every 500 hours. Maintained motors should give you 1200-1500+ hours.
 
I would not even be thinking about a bottom end.

Valvetrain and possibly risers and manifolds depending on condition.

I would also want to know why I'm bending valves / pushrods.
 
bth_Portriser.jpg
bth_Portpushrodinhole.jpg
bth_PortExhaustElbow.jpg


So this is what I found when I removed the cylinder head cover. The push rod is bent. It had gouged out the hole in the cylinder head. When I pulled it out I could see and hear some other metal parts fall off of it underneath the hole? I guess I'll figure it out when I remove the head. Try to get to it this tomorrow. Any thoughts? The riser and elbow don't seem to show any signs of water intrusion. I'll replace them anyway I guess - I've had the boat for 4 years and never replaced them, not sure when the previous owner might have. P.S. - posting these pictures is more of a pain in the butt than taking the engine apart was! Grrrr.
bth_Port5pushrodholegouged.jpg
 
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Two things come to mind that will cause a bent push rod. 1) valve face contacting piston top. This will be evident when you pull the head. You would see a contact mark on the piston. 2) Valve stuck in guide. Lack of lubrication would be the leading cause. The guides primary source of lube is splash and run. Valve guides are indirectly lubed, not pressure fed via an oil passage. Hopefully you will know more once the intake and head are off.
 
What ever you do find out what is bending rods. By looking at your pictures the heads look clean. Make sure oil is getting up there.
 
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Your manifold and riser looks fine, more hours left on them for sure. Maybe resurface them a bit at your local machine shop.
The valve might have been set up too tight in the guide from the get go. You need to check those clearances and repair the oblonged pushrod hole in your head, that hole is your pushrod guide.
 
So here's what I found when I removed the port head. Broken lifter I guess? Valve looks dark, but otherwise OK. 2nd picture is #5, 3rd picture is #7 right next door. Last picture shows the underside of the intake manifold where these parts have obviously been banging around and dented that cover I suppose. So a mechanic friend of a friend suggested I probably don't need a valve job as long as the valves seem to move smoothly and hold water, i.e., they are forming a good seal (haven't checked yet). He suggested replacing all lifters and the bent push rod, draining the oil to make sure I don't have any other metal bits down below anywhere. He thought a valve job on a 500 hour engine might cause more problems than it solved - I don't recall all the details, but it made sense when he said it. Whaddya think?
Scoflaw - I agree the manifold and risers look ok on the inside, but I've owned the boat about 5 years and never replaced them, don't know when the previous owner might have - just would make me nervous putting them back on. Can't separate the riser from the spacer.
Another question - do I need to replace the dented cover under the manifold? Didn't figure out what it's covering, ran out of daylight.
2012-11-22_11-12-12_94.jpg

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2012-11-22_13-44-22_427.jpg

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2012-11-22_11-09-16_106.jpg
 
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Now it's time to remove the valves and check the valve guide clearances as well as the seats and valve faces.

Did the rocker arm nut feel loose? I know without the tension on the pushrod due to being bent you probably can’t tell? It may have bent due to poor lash adjustment, lifter bleeding down, or the nut backing off.
 
Since you have the heads off, I would take the heads to a machine shop and have them serviced. Spending a few hundred dollars now could save you a few thousands later.
 
Time for those heads to go to the machine shop to be checked out. I wouldn't even consider a garage rebuild, unless you want to take it apart again later.

That dented thing is an oil baffle and the dents are no biggy
 
Has anyone looked for a wiped cam lobe yet? Hate to be pessimistic - but it's the first thing I'd check given the trail of broken parts there (lifter, pushrod, rocker out of position). I'd like to see a photo of the bottom of that lifter, and a shot down the bore the lifter came out of.
 
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