No compression with rocker arms torqued

[snowbrd84]

Tried again today. If I set each at tdc to 0 lash and the 1/2 turn, all cylinders great compression and starts and runs smooth and quiet. Then half the rocker bolts start spinning out.
Torquing to 40 ft lb spec leaves half the cylinders worth no compression and barely runs without giving it gas.

I see 3 possibilities.

1. Stuck lifters holding valves open.
2. Bad valve seats. Valves seat when allowed to come up further.
3. Tuliped valves seat only when no pressure on spring.

 

[stresspoint]

is it possible the cam is dialed in wrong , slightly retarded and valves will be open at the wrong time.
sure sound like this may be the issue here if all else checks out.

 

[snowbrd84]

No 1 intake closes just before timing mark on balancer when piston is at TDC. Camshaft had a guide pin as well so could only go on one way. Took old one off with gear marks pointed at each other and put it back on same.

 

[kenny nunez]

With the rocker arms removed just look closely at the top of the valve retainers to see if any are higher than the others, that will tell if any valves are tuliped.
Do not start trying different pushrods. Get the adjustable stud kit and set them @ 3/4 from the point where there is no slack but the pushrod is free to spin.

 

[snowbrd84]

With the rocker arms removed just look closely at the top of the valve retainers to see if any are higher than the others, that will tell if any valves are tuliped.
Do not start trying different pushrods. Get the adjustable stud kit and set them @ 3/4 from the point where there is no slack but the pushrod is free to spin.

Can you link me to the adjustable stud kit? Will that use same rockers?

 

[stresspoint]

No 1 intake closes just before timing mark on balancer when piston is at TDC. Camshaft had a guide pin as well so could only go on one way. Took old one off with gear marks pointed at each other and put it back on same.

View attachment 388572View attachment 388573

all looks good to me ! hmmm.

cam could be ground wrong , but i doubt that. however , anything is possible with the way how people are care free with QC these days .

thinking out aloud ? ,could them lifters have pumped up and not dampening properly.

that's all i have for the moment ,glad its you with this issue and not me!the thing would have been in bits on the bench by now .

interesting thread !

 

[snowbrd84]

And it's a month wait to even get a Mari e mechanic out here in DC area.

I am wondering about lifters too.

Here are pics of one of the bad cylinders valves. I have no clue what to look for.

 

[kenny nunez]

Look at my post #11. Also you can get more information if you google
“converting a MK5 to adjustable rocker arms”. You just need the stud and locknut kit or the “poly lock” style which are better.
I do not feel that there is a valve problem.

 

[snowbrd84]

How far before tdc on no 1 should no 1 intake valve close?

I'm pretty sure on mine it closes a few degrees before I get to TDC but then the exhaust does not start to open for quite awhile. Starting to worry I'm off a tooth.

 

[kenny nunez]

If the picture of the timing chain is your engine you have it right so that is not the problem.

 

[snowbrd84]

If the picture of the timing chain is your engine you have it right so that is not the problem.

It is but my concern that I took it off with slack on one side and put it back with slack on the other and that amounts to a tooth? Is that possible or would the rotation definitely show?

 

[tank1949]

Recently replaced camshaft and had 135-145 psi in cylinders 1-7, 180 in number 8 before.

Boat still seriously lacks power. New compression test today.

1 145
2 145
3 90
4 0
5 150
6 140
7 0
8 145

If I loosen the rocker arm bolts on a bad cylinder all the way, it goes to 145 ish psi.

Tried retorquing to 40 ftlb with cylinder at tdc. Back to zero. At my witts end with this boat. Any thoughts?

Sounds like burnt valve, piston hole or blown head gasket.

 

[kenny nunez]

If the marks were still in line you are good.

 

[stresspoint]

did you rotate the motor from the crankshaft one complete turn and recheck the marks before assembly .
not doing this is a mistake many people do , so don't feel too bad if you did not.
now , if you did not , then yes , it is possible that the slack you re calibrated may have put your camshaft in a retarded or possibly advanced position i cant figure which from your description of the slack removal ATM, but i think retarded ???.

you can check by starting @#1 and rolling the motor to TDC compression stroke one cylinder at a time and marking the balancer , not exactly scientific but it will give you an idea before you start disassemble.

as posted , it it was me it would be in bits on the bench by now.

 

[snowbrd84]

Thinking more about the cam timing being off, it would be off the same for all cylinders right? So if one intake valve not closing, none would be? I have no issues with several cylinders, so I don't think that is causing this.

 

[snowbrd84]

Update - back out here early.

Focused on a bad cylinder (5) where I could easily pull lifters with a magnet. Interestingly I had good compression on this cylinder at before I started adjust valves the other day. Then it dropped off to 0 after adjustments.
- 0 compression
- loosened intake valve - still 0 - retorqued to 40 ft lb spec
- lossened exhaust - 150 psi back
- fished out the exhaust lifter with magnet - disassembled and cleaned - pumped a bit in oil bath, nice action on plunger by hand - reinstalled - still 0 comp
- lifters not the issue.

Next - I'm looking at the intake rocker and it has a small shim at the base of the rocker bolt. Exhaust rocker does not have this. Some other rockers have them, some don't. None on cylinder 1 valves and have great comp there.

Thinking back - the shim fell off the other day when adjusting and I put it on intake valve because that's the one I thought it fell off of.

So I swap the shim to no 5 exhaust and retorque both to 40 ft lb. Bam - 150 psi on no 5 with both torqued to spec. The shims are letting proper adjustment be made while placing tension on rocker bolt threads so they lock in place. At least that's my guess.

I dunno - maybe I lost some when I did cam swap, but I don't think so.

I ordered the adjustable rocker arm conversion yesterday - I'm thinking that may get compression back on all cylinders with proper valve adjustment, but still wondering why this happened after cam install and if its a sign of some other valve issue. Old cam had more lift at .310 measured vs .282 ish on new stock spec cam. Different base circle diameters? I jave no clue. Engine was rebuilt according to PO 2 years ago but no other details available.

 

[ScottinAZ]

Update - back out here early.

Focused on a bad cylinder (5) where I could easily pull lifters with a magnet. Interestingly I had good compression on this cylinder at before I started adjust valves the other day. Then it dropped off to 0 after adjustments.
- 0 compression
- loosened intake valve - still 0 - retorqued to 40 ft lb spec
- lossened exhaust - 150 psi back
- fished out the exhaust lifter with magnet - disassembled and cleaned - pumped a bit in oil bath, nice action on plunger by hand - reinstalled - still 0 comp
- lifters not the issue.

Next - I'm looking at the intake rocker and it has a small shim at the base of the rocker bolt. Exhaust rocker does not have this. Some other rockers have them, some don't. None on cylinder 1 valves and have great comp there.

Thinking back - the shim fell off the other day when adjusting and I put it on intake valve because that's the one I thought it fell off of.

So I swap the shim to no 5 exhaust and retorque both to 40 ft lb. Bam - 150 psi on no 5 with both torqued to spec. The shims are letting proper adjustment be made while placing tension on rocker bolt threads so they lock in place. At least that's my guess.

I dunno - maybe I lost some when I did cam swap, but I don't think so.

I ordered the adjustable rocker arm conversion yesterday - I'm thinking that may get compression back on all cylinders with proper valve adjustment, but still wondering why this happened after cam install and if its a sign of some other valve issue. Old cam had more lift at .310 measured vs .282 ish on new stock spec cam. Different base circle diameters? I jave no clue. Engine was rebuilt according to PO 2 years ago but no other details available.

sounds to me as if you found your issue. From the factory, evidently they used shims to adjust the valves, and when you did the cam job, the rockers didnt go back into the exact same positions they were removed from. Looks like there is enough variation in height in the pedestals to cause at least some of the valves to partially open when torqued, causing the valve to be just enough off the seat to kill compression. The adjustable rockers should solve your issues. All in all, you CAN get compression on all cylinders with a little dinking around, so I dont think there is a bigger issue, just all of your tolerances are stacking up on those cylinders to cause the valve to not close fully.

 

[stresspoint]

good result ,
however i don't think shims are used to adjust lash in non adjustable lash engines done in the factory. usually its done by hack machine shops when they don't cut all the seats to the same measurement or when the camshaft is worn.
your model motor may have shims but in general it is not done at the factory.
with that said : changing the camshaft would have messed any shimming orientation up anyway so new shims would be needed to set the correct lash..

i am guessing the motor has at some point had a valve job that was messed up and the shims were stuck in to compensate.

 

[alldodge]

Don't have a clear understanding of the status or the motor. Old cam may have had issues and heads may have been redone, and if so measure valve steam height to see if it's within spec. If valve is to high due to incorrect seat install, seat and valve ground below spec the height will be to high

 

[snowbrd84]

Overnight adjustable rocker stud conversion and nuts from Jeggs came in today. Just installed. Has never run so smooth. Purring and not a vibe.

Went zero lash plus a quarter with irregular thread lock nuts.

Too late to leave the slip so heading home and water test tomorrow.

Dropped a spark plug in the bilge. Fished it out with magnet and a rocker bolt shim came up with it. So yeah, I must have not noticed those things and lost a few during cam swap. All my fault I guess.