350 low comp on #3

[flashback]

Did a lot of searching before I posted this, Its been a while since I've been here,,I had such good advise from folks about 5 years ago for my rebuild, that I had no need to come back, that and moving to a rural area with no affordable internet service pretty much took me out of the forum game, but here I am on a dial-up, and it's good to see a lot of the old faces... Ok, to the point, 350 pre 86 block with 4 bolt main and stock heads. The #3 cylinder has about 35# comp, and a wet plug, no water in the cylinder or crankcase, All the other plugs look good, I have not run comp test on other cylinders but will do so tommorrow and will follow the instructions that I found here on this link http://www.boatfix.com/merc/Bullet/97/97_25.pdf
I figured most likely that it is an exhaust valve that is damaged but I don't hear any unusual noise which stumps me a bit. as in my limited experience with valves, they usually get noisy when they are damaged...

Anyway, I would appriciate any help you can throw my way and in the mean time I will do some further tests and see what I come up with .................Thanks..FB

 

[jerryjerry05]

Re: 350 low comp on #3

Put some oil in the cylinder and do another comp test.No change it's probably a valve.They can get sucked or cupped and not seal right.
Actually an easy fix.No noise is OK as the valve edge is the only change and nothing is loose or broken.J

 

[flashback]

Re: 350 low comp on #3

Thanks jerry, I did the oil test and no change so I took off the exhaust manifold, then the valve cover, I found the rocker for the intake had come off the valve, The reason it happened is the rocker stud had backed out of the head enough to let the rocker jump off the pushrod and valve. At least that is what I think happened as that stud is about a 1/4 inch taller than the rest, It seems I should have heard this coming on but it never made any racket at all...So, I guess I will pull the stud completely out, make sure threads are good on stud and head, then put some locktite on it and run it back in with a couple of spare nuts locked up on it to give me something to turn it with...The rocker and pushrod do not appear to be damaged in any way, nor the valve stem.. So at this point, I'm inclined to put it back together and give it a shot..what do you folks think?

 

[6meter]

Re: 350 low comp on #3

I'll second the squirt of oil in the cylinder. A bad intake valve would pop through the carb. you won't here anything from an bad exhust valve other than a shakey motor.

 

[Bifflefan]

Re: 350 low comp on #3

run it back in with a couple of spare nuts locked up on it to give me something to turn it with

Screw in studs have a hex nut built on to them. No need to double nut to install.
Are you sure they are screw in? If not, you will need to pull the head and take it to a machine shop to get the studs pined, or have screw in studs installed.

 

[flashback]

Re: 350 low comp on #3

Actually Bifflefan, I don't know if they are threaded or pinned all I know is that it is taller than the rest..I was under the impression that they threaded but maybe not. I just stopped for lunch and thought I would check in with you guys, I'll get back at it in a bit and find out for sure...Thanks

edit: I did a bit of googling and it seems that the vast majority are pressed in as you said, Bifflefan. (thanks, that's why I came here ) seems there are some aftermarket thread in studs..I don't want to change them all out, so if that is the case, whats the chances of threading the existing hole and go with a screw in stud on just this one valve? These are cast iron heads and I am not sure if that is something I can do with a standard tap, I have threaded steel a few times but never tried cast...

 

[Adirondack]

Re: 350 low comp on #3

Actually Bifflefan, I don't know if they are threaded or pinned all I know is that it is taller than the rest..I was under the impression that they threaded but maybe not. I just stopped for lunch and thought I would check in with you guys, I'll get back at it in a bit and find out for sure...Thanks

It's doubtful they are threaded studs. It's tuff to pull a pressed stud with stock springs. Threaded are really tuff. Depending on how far it's pulled, and if you only want to do that one it could probably be pinned without removing the head. Access to a straight angle on the stud tower would determine that.

 

[Alpheus]

Re: 350 low comp on #3

A bad intake valve would pop through the carb.

Yes an intake valve not sealing would make a pop through the carb, but in his case the valve is not opening at all. No symptoms but a dead cylinder do to no air/fuel being let into the combustion chamber to compress and burn...

 

[flashback]

Re: 350 low comp on #3

Thanks Adirondack, you were replying as I was editing... So If I read you right, I can knock this stud back in and then pin it? I'm not understanding the mechanics of the pinning procedure? What would that involve?

 

[Alpheus]

Re: 350 low comp on #3

Personally I would remove the old studs and put in threaded ones. Its pretty easy to remove the old ones by just lubing up the stud,stacking washers on the stud and tightening the rocker nut until it bottoms out on the threads. Remove the nut and add another washer and repeat until the stud pulls up out of the head. Then just run a tap in the stud holes and thread in the new studs.

But if you insist on pinning.

To pin the studs all you need is an 3/32" drill bit and some .097" split or roll pins from the hardware store. Drill into the stud boss about 1/3" down from the top. Most people drill through the boss, but it is not really needed. As long as you go through the stud and into the other side of the boss far enough for the pin to hold you are OK.

Here is a kit that helps with the process...

http://www.goodson.com/store/template/product_detail.php?IID=2948&&

 

[Adirondack]

Re: 350 low comp on #3

Thanks Adirondack, you were replying as I was editing... So If I read you right, I can knock this stud back in and then pin it? I'm not understanding the mechanics of the pinning procedure? What would that involve?

Just as Alpheus says. Threaded stud is the better way. Either way works, and one really no more difficult than the other.

 

[flashback]

Re: 350 low comp on #3

OK, got ya, after studying it a bit I figured that might be the answer but just wanted to be sure, I have all the stuff I need right in the shed so I'm good to go..Thanks a bunch and great drawing Alpheus..

I was reading up on adjustment afterwards, and my source says to tighten the rocker nut down until I can't turn the push rod, then go 1 turn further. that said, the rest of the valves are not that tight, with the lifter on the base of the lobe, any one of the rockers has a slight wiggle and I can turn the pushrod. this seems odd that they would all be loose so my question is, is Clymer's steering me wrong? They have before but I wouldn't think they would screw up this...Or, have all the studs slipped a bit? I shy away from the screw in studs only because of the shavings it will create. I probably should take the heads off if that is the way I go...

 

[Adirondack]

Re: 350 low comp on #3

OK, got ya, after studying it a bit I figured that might be the answer but just wanted to be sure, I have all the stuff I need right in the shed so I'm good to go..Thanks a bunch and great drawing Alpheus..

I was reading up on adjustment afterwards, and my source says to tighten the rocker nut down until I can't turn the push rod, then go 1 turn further. that said, the rest of the valves are not that tight, with the lifter on the base of the lobe, any one of the rockers has a slight wiggle and I can turn the pushrod. this seems odd that they would all be loose so my question is, is Clymer's steering me wrong? They have before but I wouldn't think they would screw up this...Or, have all the studs slipped a bit? I shy away from the screw in studs only because of the shavings it will create. I probably should take the heads off if that is the way I go...

Clymers is telling you right. Although I usually go 3/4 turn. No real difference. I wouldn't worry about the adjustment on the others too much. If they were really off the motor would have clattered like crazy. They have hydraulic lifters. Meaning they pump up with oil pressure.
If your uncomfortable with the status of the other studs about the only thing you can do is tap, or pin them all.

As far as shavings go you will most likely produce more drilling for a pin. covering your pushrod holes, and running a shop vac while drilling or taping should help with that. If your more comfortable removing the head that's also your option. I'm just trying to put you back on the water with as little fuss and expense as possible.

Good luck, and happpy boating.

 

[Alpheus]

Re: 350 low comp on #3

Here is a video I made that shows you how to adjust the valves. Yes its on a 3.0 but its the same procedure for adjusting them on your 5.7 its just in a different order and you give one complete turn on the nut instead of 3/4. If you want to adjust the one rocker, just bring that piston up on TDC during compression stroke. You can adjust both rockers then if you want...

http://forums.iboats.com/showthread.php?t=435011&highlight=rocker+adjustment+video

 

[flashback]

Re: 350 low comp on #3

Wow, talk about above and beyond the call, thankyou all very much..this site was a life saver for me 5 years ago and it has done nothing but get better..unfortunately, couldn't watch the video as dial-up doesn't do well with that, but never the less, I'm comfortable with where I am...

I finished pinning the wayward stud last night, and tested the comp, it's back to 150lbs so all seems good, I'll button it up today and go for a ride if the rain will let up...This old Chris may outlast me yet...:lol:

 

[flashback]

Re: 350 low comp on #3

Much thx guys! got it buttoned up and went for a spin..runs very good.........
FB