1986 Mercruiser 140 Blown Head Gasket?

[Swimforshore]

Bruce you are correct the L1 is advanced engine performance. i would choose cat and sensor safe chemicals on fuel injected engine but that is a topic for another thread.

I'm thinking those compression numbers don't make sense because if #4 were truly that low it would run so bad you wouldn't take her out on the lake, but 4 is low enough to warrant further testing

The CLT numbers don't add up either, you need the cylinder being tested on tdc with the valves closed removing valve cover makes it easier to see where the valves are and a screw driver will help find tdc. You want low numbers under 20% under 10 would be great.

Once CLT is properly connected you can listen for where you're loosing your air.

If you can post some pics of the valves, spark plugs, and anything else interesting

 

[Swimforshore]

You could remove your rocker arms that wouldn't allow any of the valves to open and avoid confusion. Then you only need to worry about tdc

 

[bruceb58]

Get TDC compression stroke on #1,and test. Then rotate engine 360? and check #4.

Then get TDC on cylinder #2 test and then rotate engine 360? and test #3.

4 cylinder engines are the easiest. to test. With the exhaust/intake manifold off, you will easily be able to tell where the air is coming out if you have it broken down that far.

 

[bruceb58]

You could remove your rocker arms that wouldn't allow any of the valves to open and avoid confusion. Then you only need to worry about tdc

Seriously? I guess since the engine is going to be taken apart anyway. It's really not that hard to figure out and a 4 cylinder is a piece of cake to do it correct.

 

[bruceb58]

When injecting air into each cylinder (~20 psi, #1 at TDC compression),

You can only inject air for the #1 cylinder. You then need to rotate the crank before you test any others.

 

[Swimforshore]

Seriously? I guess since the engine is going to be taken apart anyway. It's really not that hard to figure out and a 4 cylinder is a piece of cake to do it correct.

Just thinking motor is already partially torn down, and it would eliminate chance of being 360 out. You could also do 2 cylinders without moving the crank. These tests are easy for someone who has done it before and knows what to look for but can be tricky for a novice.

 

[pvovk]

I did do it correctly earlier (TDC) compression on each cylinder. Just now, I removed the rocker arms and on 7 of the 8, I feel a fair amount of air escaping the port through the valve. So much that I can't stop it with my hand trying to seal the port. The inlet pressure was 25 psi. Just seems like the valves are not good. No more time now, but hopefully later tonight, I will blank off the ports and see if I get any air between cylinders (via head gasket) or air from the oil dipstick (rings).

 

[nola mike]

, I feel a fair amount of air escaping the port through the valve. So much that I can't stop it with my hand trying to seal the port.

What do you mean when you say "port"? And how would you block it with your hand?

 

[Swimforshore]

What do you mean when you say "port"? And how would you block it with your hand?

From what I understand intake and exhaust manifolds are off so he can stick his hand right over the ports in the head.

 

[nola mike]

Duh. Don't know why that didn't register. But unless he wiped out 7 valve springs, that's still fishy. And if you had that much air escaping, you probably wouldn't get the 110+ psi on the compression..

 

[Swimforshore]

I did do it correctly earlier (TDC) compression on each cylinder. Just now, I removed the rocker arms and on 7 of the 8, I feel a fair amount of air escaping the port through the valve. So much that I can't stop it with my hand trying to seal the port. The inlet pressure was 25 psi. Just seems like the valves are not good. No more time now, but hopefully later tonight, I will blank off the ports and see if I get any air between cylinders (via head gasket) or air from the oil dipstick (rings).

You should be running inlet pressure closer to 100 psi. Get that cylinder up around operating pressure. Is the air leaking out intake or exhaust ports or nothing? On a car bad head gaskets will push coolant out of the radiator opening. Never tried it on a boat, but I would imagine you could pop one of the outlet hoses and listen or watch for it to push out water. Sounds like it's time to pull the head and send it off to the machine shop.

 

[Swimforshore]

Duh. Don't know why that didn't register. But unless he wiped out 7 valve springs, that's still fishy. And if you had that much air escaping, you probably wouldn't get the 110+ psi on the compression..

I agree numbers don't add up, with that much leakage I don't think it would run. I think it's due to the low inlet pressure. My theory goes: a cylinder will leak x no matter what pressure you are running, if airflow volume into the cylinder is low, x will escape and low - x = bad low reading. Can't say for sure never tried CLT at that pressure.

 

[pvovk]

I blocked off the ports the best I could at the moment (piece of wood bolted on with the manifold gasket. Good enough to prove a head gasket breech between #2 and #3. Took off the head. Head gasket split between #2 and #3. Exhaust valve on #4 cylinder (the one with super low compression), is missing part of the valve, maybe 1/8" or so cut off one side. Off to the machine shop Thursday. I am hopeful that with a good head, etc. the engine will run great and idle smooth.

I agree the values I was obtaining didn't make sense (maybe the pressure was too low to help seal the valves), but at least I could confirm that the gasket was blown between #2 and #3. The compression in #4 was always way too low and now hopefully, it's totally due to the broken valve. Maybe the other valves are ok after all. I'll leave all that to the machine shop.

More and hopefully, final questions:
1. Do you recommend re-torquing the head bolts after it has warmed up (and then re-torque while warm or after it's cooled down)? The Seloc manual doesn't mention re-torquing but I've seen elsewhere that it is recommended.
2. Is Perfect Seal what I should use to lubricate and seal the threads and bolt heads on the head bolts (I have a whole can of it)?
3. Is the valve lash only set cold or is it also re-checked while running listening for noise and adjusting accordingly?

Thanks again for the many and prompt replies. Those have been very helpful. I will definitely post an update on how it runs when it's all back together.

 

[alldodge]

1) No, don't retorque
2) Yes, use perfect seal
3) Being a 1986 motor you would torque rocker nuts to 20 ft lb using the below method



Here is a link to the manual
http://boatinfo.no/lib/mercruiser/manuals/mercruiser8.html#/0

 

[Swimforshore]

Perfect seal on head bolts? I would recheck the service manual, I have never seen a head bolt call for sealer the manual usually wants them oiled.

 

[Swimforshore]

Perfect seal on head bolts? I would recheck the service manual, I have never seen a head bolt call for sealer the manual usually wants them oiled.

Found the Mercury service manual online, it says to coat the threads of the head bolt with perfect seal and to retorque after 20 hours of operation.

 

[alldodge]

perfect seal

 

[Swimforshore]

Alldodge curious about the manual you have does it say retorque is needed? The manual I saw said head bolt torque was 90lbft at final step. I would feel better about 130 with no retorque

 

[fishrdan]

Look up the 140 HP head torque specs, should be 90 FTLB on the final step from what I remember. Pics posted up look like a 470, not a 140 the OP is working on.

Yes, dip the head bolts in Perfect Seal before installing them. Raw water in the block will rust the bottom of the head bolts otherwise. I wouldn't bother re-torquing the head bolts, unless the new head gasket literature states that it needs to be re-torqued. The old (1970's) steel shim gaskets may have needed re-torquing as stipulated in the old manual, but the new style composite gasket shouldn't need re-torquing.

Buy a Fel-Pro head set and it should have all the gaskets you need, except maybe the manifold and riser gaskets. I bought a Victor Reinz 140HP head set once and it was missing a couple seals for the rocker cover......

Also, the rocker arms need to be adjusted, not torqued. Either set them cold, or adjust them once the engine is running. Both ways work.

BE SURE!!!! To mark where each lifter comes from so it goes back onto the exact same cam lobe it was removed from. (You need to do this or a mis-matched lifter/cam lobe could wipe out the cam lobe.) Myself, I grab some baggies and write on them with a sharpie so I know where it came from 1I, 1E, 2I, 2E, or just 1-2-3-4-5-6-7-8. Place the lifter, push rod, rocker and nut into each bag, so everything goes back together exactly as it came apart. (You need u could wip

 

[bruceb58]

I agree with Fishrdan. I have the OMC and Volvo manual for the exact same engine. The OMC specs 90-100 ftlbs and the Volvo specs 95 ftlbs.

The picture of the engine in post #34 that Dodge does not look like the correct engine. I agree with Fishrdan on this as well. That looks like the 470 engine. On a 3.0, the oil filter is in front of the distributor. the 470 is reversed.

Permatex #2 can be used on the head bolts instead of perfect seal.

Just looked at the Mercruiser manual and it does say to re torque at 20 hours.