RE: Issues with Mercruiser 5.0 LX 4 Barrel Carb

[BusinessConnected]

How did you set the nuts on the rocker arms just torque to a value?

It was more Tightening until they matched the images I had with the Rocker Covers off.. Whilst also ensuring they were obviously tightish etc..

 

[Lou C]

Ok if you have a pre Vortec engine (‘95 and older) the valve train is adjustable and you HAVE to adjust the hydraulic lash adjusters. The later engines have non adjustable valvetrain & those you just torque to spec.

 

[dubs283]

I basically took photo's of what I had to begin with.. and re-installed with Bolts at around the same depth/levels etc..

I didn't do Valve Clearances etc as I just took the Heads Themselves off and re-install as they were.

That's not good

It was more Tightening until they matched the images I had with the Rocker Covers off.. Whilst also ensuring they were obviously tightish etc..

Not even close to properly adjusting valve lash.

This project may be outside your scope. Unless you have at least an oem manual with no prior experience setting lash, pictures won't help you

 

[Lou C]

While getting the distributor installed properly & adjusting the hydraulic valve lifters at first seems confusing if you watch enough vids it will start to make sense. When I replaced my cyl heads I had done mechanical valve clearances on VWs, Hondas, Mazdas but never did a Chev with hydraulics. It was actually easier! There is a 2 step method in the shop manual (OMC in my case but probably lifted right from GM) that I followed. I labeled the Cyl #s & the Intake & Exhaust valves to eliminate confusion. The basic idea is to get #1 at TDC on the compression stroke so both valves will be closed. Then you loosen the rocker arm nut till you can just move the pushrod up n down, then tighten till that up & down motion just stops. That’s zero lash. Then give it one full turn; that puts the plunger in the lifter in the middle of its travel. Then following GMs procedure adjust the rest of the intakes & exhausts that can be adjusted with the engine in the starting position. Next will have to turn the crank one more time as per GM instructions to get the 2nd half done. I know confusing but it’s really not hard. It is easiest if you have the intake & distributor installed with the cap off so you can watch the position of the rotor…..

 

[stresspoint]

i still sometimes set the lash with the motor running > back each nut off till it clacks then wind it down 1/2 a turn.
love the smell of burning oil on a hot extractor .

 

[BusinessConnected]

Updates Guys:
Took the Boat to my local Mechanic who's familiar with older 305 Engines etc and he's adjusted the Lash/Timing for me.
Boat is running now ok out of the water.

I didn't realise myself the Button on Side of Throttle to allow you to choke/start at higher RPM... I've always tried to start at idle position only which may have been some of my issues.

Anyhow had it out on the Water today and it was ok at idling, Changing into Forward/Reverse was ok, however It wouldn't get past around 2800-3000rpm.

As such being a larger Boat... it wouldn't get on plane etc.
When not in gear the engine would happily get to 5000RPM without issue (only briefly tested for 2 seconds or so... nothing sustained).

Also there was a bit of Water Vapour coming out top of Flame Arrestor.. Not certain whether this was just steam from condensation that may have formed from sitting around for long periods etc.

Any further ideas on where to head?

 

[dubs283]

had it out on the Water today and it was ok at idling, Changing into Forward/Reverse was ok, however It wouldn't get past around 2800-3000rpm.

You had the heads off and replaced the head gaskets, correct? Did you send the heads out for inspection/rebuild?

Seeing as how valve lash and timing are now set proper (guessing your mechanic did this correctly) my next step would be a compression/leak down test

 

[BusinessConnected]

You had the heads off and replaced the head gaskets, correct? Did you send the heads out for inspection/rebuild?

Seeing as how valve lash and timing are now set proper (guessing your mechanic did this correctly) my next step would be a compression/leak down test

Compression Test has been done previously….
I’m at 120PSI or above on all cylinders except 3 which is around 80PSI Now.

 

[dubs283]

Compression Test has been done previously….
I’m at 120PSI or above on all cylinders except 3 which is around 80PSI Now.

Okay, that proves the engine isn't sound and you can expect results that you're experiencing. A leak down test on #3 will point you in the right direction, valves or rings, maybe both.

My guess is tuliped valve(s) at a minimum

FYI 120 psi is a tad low for sbc, should be seeing closer to 150 for good compression

 

[Lou C]

If one is at 80 psi that’s too low. A small block Chevy in good shape should have compression #s of approx 150; but it you did the comp test on a cold engine it would not be that accurate. Warm up engine set throttle wide open, remove spark plugs & disable ignition.
After I replaced the cyl heads on my old 4.3 V6 & adjusted the hydraulic lifter preload my comp test results were approx 165.

 

[Scott Danforth]

Compression Test has been done previously….
I’m at 120PSI or above on all cylinders except 3 which is around 80PSI Now.

You have a core motor. You can either get your motor rebuilt, trade it in as a core for a new long block. However with compression that low you are down on power

 

[Lou C]

PS
one hydraulic lifter being adjusted too tight can cause a valve not to close all the way and that can cause low compression. Heads were checked by a machine shop? It is common due to leaky inboard wet exhaust that you can have sticky valves causing lower compression.

 

[Lou C]

PPS
I went back and looked at the beginning of this long thread and your exhaust elbows looked HORRIBLE, (way past replacement time) it seems quite likely that you had water leaking into your cyls, causing sticky valves, if the heads have not been off, do a leak down test and see what it shows, but I think you will wind up having to do at least a valve job, if not replace the heads, due to a bad overheat (burnt up flappers). Bad overheats on small block Chevrolets usually result in cracked cyl heads. That's what led to me having to replace mine....

 

[dubs283]

it seems quite likely that you had water leaking into your cyls, causing sticky valves

Not a valid reason for a sticky valve. A sticky or stuck valve is most often the result of excess deposits on the valve stem/guide or an issue with the spring/adjustment

Water intrusion to the combustion chamber most often caused from faulty exhaust manifold/riser will cause the temperature in the combustion chamber to increase resulting in a deformation of the valve head/seat, e.g. tuliped. If the water intrusion is bad enough you will note washing of the combustion chamber, in essence the area will be steam cleaned

 

[Lou C]

Not a valid reason for a sticky valve. A sticky or stuck valve is most often the result of excess deposits on the valve stem/guide or an issue with the spring/adjustment

Water intrusion to the combustion chamber most often caused from faulty exhaust manifold/riser will cause the temperature in the combustion chamber to increase resulting in a deformation of the valve head/seat, e.g. tuliped. If the water intrusion is bad enough you will note washing of the combustion chamber, in essence the area will be steam cleaned

Well on mine, I had blown HGs putting water in 2 cyls not enough to hydrolock but when I took the heads off it was obvious. The engine would start, run rough, then after about 5 min smooth out. When it cooled off they would get sticky again. You can also get rust on the stem, that for sure will cause a sticky valve.

in my pix of the removal of the stbd side head you can see one of the valves stuck open....
going back to the pic of the OP's elbow, it was probably one of the worst I have ever seen, there is no way that was not leaking water back into the engine....
you can also see it in my pic of the old cyl heads in the back of my Jeep, notice the height of the valve stems, a few are obviously lower....

 

[dubs283]

You can also get rust on the stem, that for sure will cause a sticky valve.

Fair enough. This may have been the culprit in your case, among other things.

You'll note I use the phrases "most always" and "rarely" in many of my posts. This is due to the nature of this forum, I cannot see first hand any poster's equipment. I must rely on information provided and my past experience. Of which includes a thought process of disregarding words such as "always" and "never"

A lot of the information on this forum is for posterity. Anyone can retrieve this information and use it to their advantage, therfore it is pertinent to focus on what statistically has the greatest value for causation of an issue. Again I can only relay information based on my past experiences and any/all pertinent service information.

My biggest issue with this forum is how many people will read some or all of a thread and relate information regarding their experience on equipment that does not necessarily match what the OP has. Certainly all four stroke engines share some commonality but there are definte issues that can pertain specifically to what an OP is working on and have very little/nothing to do with a poster's equipment/experience.

You obviously had a severe water intrusion from possibly multiple sources. Many people here would be quite surprised how much damage a little amount of water in the combustion chamber can cause a marine engine in a short time span

 

[BusinessConnected]

Guys:
I'm now looking into a Repower for this boat.
I've found a Vortec 5.7L which looks promising from local rebuilder.
I'm waiting for answers based on my question to him but thought I'd post here also..

I'm assuming with this Engine I'd need to
- Get Replacement Intake Manifold to suit?
- Perhaps get Replacement Carb? (or would that be changeable?)
- Can Thunderbolt IV be used with Vortec Engines... or should I look at alternative Control?

Otherwise I believe I'd just need to move Fuel Pump and Ancillaries across from Original Engine etc..

 

[dubs283]

I'm now looking into a Repower for this boat.

Awesome!

Can't help you with info regarding a replacement long block but..

What was the failure in your current engIne that requires the replacement?

 

[BusinessConnected]

Awesome!

Can't help you with info regarding a replacement long block but..

What was the failure in your current engIne that requires the replacement?

It’s low power on engine… low compression on Cylinder 3 and water vapour/steam coming out of Flame Arrestor.

 

[dubs283]

… low compression on Cylinder 3

Understood

What caused the low compression?