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2002 5.0L Carbed valve adjustment (over tight issues?)

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BackEastDon

Member
I signed up for this forum a while back to search through stuck valve issues. A boat I am under contract to purchase ended up with a stuck valve in one cylider from water intrusion that was discovered commissioning the boat this spring. Engine is a 2002 5.0L 2bbl. The head was removed and reconditioned at a reputable marine machine shop (according to the surveyor). We've reviewed the work order and parts invoices and all looks done properly with new head bolts, risers, manifolds and such. The intake manifold was inspected and pressure tested as well. The engine work other than machine shop was performed by the sellers son who is ASE GM certified.

During the survey the engine compression test measured 185-190 across all cylinders. Rest of boat is clean, dry and solid. There is always a but. During the seatrial the engine combustion intermittently was popping through the carb at 4200 rpm. The surveyor suspected the valves were set a bit too tight. It otherwise starts and runs smooth. I am awaiting the seller to get the issue resolved and will go out on a second trial.

Would appreciate some insight from those more familiar with this engine. Last pushrod V8 I did heads on was a 69 Chrysler (many, many years ago).

Thoughts? Advice?
 
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So, suspected water ingestion and only remove 1 head?
Backfiring thru the intake could be a mis-adjusted valve but the hyd lifter should be able to overcome a slight misadjustment
Rocker readjustment/check should be next and if the problem remains the backfiring is caused by a bad valve in the other head
 
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BackEastDon said:
I signed up for this forum a while back to search through stuck valve issues. A boat I am under contract to purchase ended up with a stuck valve in one cylider from water intrusion that was discovered commissioning the boat this spring. Engine is a 2002 5.0L 2bbl. The head was removed and reconditioned at a reputable marine machine shop (according to the surveyor). We've reviewed the work order and parts invoices and all looks done properly with new head bolts, risers, manifolds and such. The intake manifold was inspected and pressure tested as well. The engine work other than machine shop was performed by the sellers son who is ASE GM certified.

During the survey the engine compression test measured 185-190 across all cylinders. Rest of boat is clean, dry and solid. There is always a but. During the seatrial the engine combustion intermittently was popping through the carb at 4200 rpm. The surveyor suspected the valves were set a bit too tight.
Contrary to the misconception out there (i.e., adjusting valves), we DO NOT adjust valves on this engine.
We adjust the hydraulic cam follower plunger depth by adjusting the rocker arm stud nut, of which controls the depth of the plunger at ZERO valve lash.
An incorrect (spelled too tight) adjustment may lead to a valve that is not fully seating, resulting in a burned valve or valve seat.
In other words, a rocker arm stud nut that has been set too deeply may cause the cam follower's plunger to bottom out. This typically results in a valve that is NOT allowed to fully seat! If so, it does not take long for the seating area to become damaged.

It otherwise starts and runs smooth. I am awaiting the seller to get the issue resolved and will go out on a second trial.
see below **

Would appreciate some insight from those more familiar with this engine. Last pushrod V8 I did heads on was a 69 Chrysler (many, many years ago).
If you know the basics of the push-rod engines, you know how important it is to make certain that the cam follower adjustment is done correctly!

Thoughts? Advice?
Click to expand...

My suggestions:

..... Always perform a cylinder leak-down test before removing cylinder heads. Once the cylinder head(s) have been removed, this opportunity is gone!

..... Always adjust the push-rod style V-8 engine cam followers using the Static 8 stop procedure. (best when done prior to the followers being oil primed)
The 2 or 3 stop procedure is not nearly as accurate!

..... The best (although messy) method would be using the dynamic adjustment procedure.


..... ** since you may purchase this boat, I would suggest getting yourself very involved in the repair process! You will end up living with this repair.... and it could be great, or it could be not so great! Learn how the "fix" is being taken care of! If you do not like the suggested fix, don't hold back.... voice your opinion!


Good luck!





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Bt Doctur said:
So, suspected water ingestion and only remove 1 head?
Backfiring thru the intake could be a mis-adjusted valve but the hyd lifter should be able to overcome a slight misadjustment
Rocker readjustment/check should be next and if the problem remains the backfiring is caused by a bad valve in the other head
Click to expand...

Based on the read of the machine shop work order, the issue occurred with the valve closed and then rusted over the winter. So not exactly water ingestion at least into the cylinders. Both risers and manifolds were removed and a compression test was done to both sides prior to removal of heads. There were no signs of water on the other side. While I would have preferred both heads be sent to the shop and would have done it that way if it were me, I don't own the boat and as buyer can only dictate to a point. With the compression as it tested both from the seller and surveyor matched, I am inclined to agree with them that the valve seats should be good. The surveyor commented to the seller that adjustment is more feel than measurement.

I'll probably find out soon enough as the seller is still on the hook for delivering a boat that is running correctly regardless. The backfiring is subtle and intermittent. You could almost miss it from the pilot house with the engine cover on. Probably why the seller missed it when he took it out after the engine went back together. I also don't think he attempted to get up to 4500 rpm perhaps.
 
RicardoMarine said:
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My suggestions:

..... Always perform a cylinder leak-down test before removing cylinder heads. Once the cylinder head(s) have been removed, this opportunity is gone!

..... Always adjust the push-rod style V-8 engine cam followers using the Static 8 stop procedure. (best when done prior to the followers being oil primed)
The 2 or 3 stop procedure is not nearly as accurate!

..... The best (although messy) method would be using the dynamic adjustment procedure.


..... ** since you may purchase this boat, I would suggest getting yourself very involved in the repair process! You will end up living with this repair.... and it could be great, or it could be not so great! Learn how the "fix" is being taken care of! If you do not like the suggested fix, don't hold back.... voice your opinion!


Good luck!





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Click to expand...
Thanks, I did manage to get a lot of info just poking through the site with various searches. It all became pretty specific last week at the seatrial. Also the explanation on the adjustment helped with providing some added detail. We had just idled off the dock out to open water and made the first run up past 4k. The surveyor keyed into the problem immediately and we shut the engine down. Engine cover was opened and the surveyor went over the engine for hot spots and anything else out of sorts. A second run was attempted slowly up to 4200rpm and it was obvious there was an issue. It was not super obvious to us in the pilot house that there was an issue. It was not till we ran it with the cover open that I heard what the surveyor caught on the first run. Certainly not a backfire as I am used to hearing. Much more like a pffttt intermittently.
 
Certainly not a backfire as I am used to hearing. Much more like a pffttt intermittently.
Click to expand...

Ayuh,..... Inspect the Contents of the fuel filter for Anything, but clean fresh gasoline,.....

Sounds like it's goin' lean at high demand,....
 
Update: Seller had the valves lash adjusted by another mechanic. Some performance improvement but not quite there yet. Mechanic thought the fuel was probably the issue as the boat has sat a bit. Tank was drained of old fuel and fresh fuel added. Got the report this morning it is ready for the second seatrial scheduled for tomorrow.

Surveyor also seemed to think the prop might be oversized for the boat. Been trying to figure out the OEM prop size. The boat has 4 props the seller has for it. I'll measure them and decide. The Mercury site lists between 14 and 14.5 inch props in the calculator and there is a 15 on it. Figure if oversized and I can get to 4500 rpm, I should be good.

Thanks all for the input.
 
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BackEastDon said:
Update: Seller had the valves lash adjusted by another mechanic. Some performance improvement but not quite there yet.
We make this adjustment beginning from ZERO valve stem to rocker arm lash.
Once ZERO lash has been determined, the further adjustment of the rocker arm stud nut sets the depth of the cam follower's hydraulic plunger.
This is the goal...... setting the depth of the plunger within the follower's body!

IMO, the 2 or 3 stop static procedure is not nearly as accurate.
The 8 stop static procedure is very accurate, and should always be used.

If I were you, I would want to know what procedure was used!



Mechanic thought the fuel was probably the issue as the boat has sat a bit. Tank was drained of old fuel and fresh fuel added. Got the report this morning it is ready for the second seatrial scheduled for tomorrow.
Just to be clear......... this mechanic thinks that old fuel is the cause of popping through the carb at 4200 rpm?????


Surveyor also seemed to think the prop might be oversized for the boat. Been trying to figure out the OEM prop size. The boat has 4 props the seller has for it. I'll measure them and decide. The Mercury site lists between 14 and 14.5 inch props in the calculator and there is a 15 on it. Figure if oversized and I can get to 4500 rpm, I should be good.
Yes.... correct prop size/pitch is determined by seeing if the engine will reach the prescribed WOT RPM.
The catch is..... the engine must be healthy and in full tune in order for this test to be accurate.
In this case, the first thing to clear up is the issue with the engine's performance.

Thanks all for the input.
Click to expand...


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I set a test parameter of 4600 rpm to be met without issue with the seller. I've control of little else. Given what I've gathered on the prop I've been told every addition to pitch cost 100rpm without factoring in diameter increase. It may only get to 4500rpm if the surveyor is right about the prop.

It is not ideal by any stretch. Going on a hunch and what I heard from the engine on the first trial. Even if this means pulling both heads off myself and doing them all over again. It is probably worth it. I heard nothing that convinces me this engine is toast. Above average condition boat according to the survey, 300 hours on the engine and now lots of new parts. Option B is to start looking all over again for a boat that is hard to find in good condition. This one was two years in the search.
 
Hope it works out for you.

Jeff

PS: Another reason for popping through the carb is a worn cam lobe--easy to spot with the intake off.
 
Seatrial went without a hitch. Not a hickup with the engine. WOT reached just over the 4600rpm mark on the tach. Got up on plane quickly from multiple dead starts. Didn't struggle. Not so much as a shudder from it. Idles smooth, fires right up. Signed the acceptance and am arranging to transport it home. I'll be sure to update one way or the other after I've run it a bit.

Thanks again all.
 
Another reason for popping through the carb is a worn cam lobe--easy to spot with the intake off.
Click to expand...

FYI..... a 2002 GM 5.0L would be fitted with a roller cam.
I won't suggest that this is not possible, but I have yet to see a worn roller cam lobe. ​



BackEastDon said:
Seatrial went without a hitch. Not a hickup with the engine. WOT reached just over the 4600rpm mark on the tach. Got up on plane quickly from multiple dead starts. Didn't struggle. Not so much as a shudder from it. Idles smooth, fires right up. Signed the acceptance and am arranging to transport it home. I'll be sure to update one way or the other after I've run it a bit.

Thanks again all.
Click to expand...

Good for you. I wish you years of happy boating. :D


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