vibration and overheating at gm 350 (one piece rear seal carburated)

[sarantis]

Brand new block 260 Hp.I swaped from MCM 228 1979 (2 pieces rear seal) to a "supossed " brand new 5.7L 260Hp doing some conversions to the flywheel cover and to the intake manifold.As you know the later block has the center holes at a different angle and since i couldn't spend more money i made 4 brass sleeves-spacers at an oposite angle and i thought that the manifold steped very well on the block.(Someone here had advised me to do it someone else not).Even from the start of the new block it had vibrations not evident at all rpm range but i can't say if it had overheating problems because from first round i had forgotten to place the plastic water inlets at the lower unit and because i wanted to go fishing i put them at night the oposite way.Being next day slightly on plane i noticed the needle next to the red region.One piece of the impeller was destroyed but not cut.After that i bought a brand new outdrive SE106 and I've double checked everything exept of the water shutters or clogged Ypipe but unlikely to have problem because both parts of the pipe have the same temperature.I adjusted the valves ,checked the sparks and Finally i was obliged to check compressions something i would have done when i bought the motor.The numbers i got are the followings : 2 4 6 8
200 200 195 200
(with the engine cold)
1 3 5 7
205 200 195 205
I thing something is not ok with these numbers.My friend replaced his head gaskets at an older 350 ang got exactly 160 at all cylinders.Anyway i continued the searching and found that when pulling the fire cable from #5 the rpm and vibration doesn't change at all whereas when pulling #6 the change is very slight and at the rest of the cylinders the rpm change is obvious.May a bad steping of the intake influence the compressions?But if the placing of the intake was n't good at the center wouldn't i see exhaust gases from the crossover points? Please experts give me some help.It's about three years since i bought it and still i can't run on the water!

 

[Bt Doctur]

Re: vibration and overheating at gm 350 (one piece rear seal carburated)

"doing some conversions to the flywheel cover and "
Exactly what does that mean? constant vibration may be a mis-matched flywheel or coupler

 

[sarantis]

Re: vibration and overheating at gm 350 (one piece rear seal carburated)

i went from the old coupler and small flywheel to the triangle coupler and bigger flywheel because of the different rear seal.To fit them i had to "eat" a litle the flywheel cover.I checked alignment with hand made tool.But this even wrong can't affect the cylinders beaviour or overheating .Right?

 

[sarantis]

Re: vibration and overheating at gm 350 (one piece rear seal carburated)

Anyway this evening i went again for a round.When i planed the boat air bubles got in the cooling system (i've put clear hosesat the exhaust manifolds) so most possible problem are the head gaskets i think.But what about the compression numbers? Have you ever met a brand new 350 (old style,not vortec) with such high compressions?

 

[searay3]

Re: vibration and overheating at gm 350 (one piece rear seal carburated)

problem 1...it must have other than stock pistons and possible head work to get those kind of numbers. If the comp gauge is accurate you'll have to run hi octane fuel. May want to pull a head or heads and see what you got. Problem 2...a lean condition will absolutely make it run hot. If you were fooling with the fitment of the intake manifold, a leak where 5 and 6 meet the heads could cause the ruff running and overheat. You really need the proper head/intake fit so it seals properly and flows air like it should. (If I understand what you wrote)....

 

[sarantis]

Re: vibration and overheating at gm 350 (one piece rear seal carburated)

Thanks for replying searay3.You 've well understand although my english is not perfect.I agree with your suggestion for a proper fitment head/intake but do you believe the head gaskets may be good?Can an overheat due to lean condition make the water boil so that i see air bubles through the clear hoses without having the head gaskets burnt?

 

[Bondo]

Re: vibration and overheating at gm 350 (one piece rear seal carburated)

When i planed the boat air bubles got in the cooling system (i've put clear hosesat the exhaust manifolds) so most possible problem are the head gaskets

Ayuh,... Air in those lines is not necessarily indicative of a failed headgasket...
I donno why the Compression #s are so high,...
But I don't see a Bad headgasket there Either....

The Trashed Impeller,..?? Did you find ALL the pieces,..??

I know those intakes can be modified to fit as you've done,... But I've never tried it...
Donno....
Lean is Bad,... Do the sparkplugs tell a story with their Colors,..??

 

[sarantis]

Re: vibration and overheating at gm 350 (one piece rear seal carburated)

Thank you Bond-O.The traashed impeller was all in its housing.But apart from this i've double checked every line,new thermostat housing relatively new manifolds,risers,circulator.I think i have to find out why #5 and #6 have lower compressions and i '' double check the high compressions with another gauge.Please keep in touch.

 

[sarantis]

Re: vibration and overheating at gm 350 (one piece rear seal carburated)

as about the spark plug analysis i went them to a mechanic to read them and he told me it's bad mixture bad i cant remember if it's color matched with a possible bad fitment of the intake at the #5,#6 fuel passages.I'll serch a little more and i'll let you know.

 

[Bondo]

Re: vibration and overheating at gm 350 (one piece rear seal carburated)

as about the spark plug analysis i went them to a mechanic to read them and he told me it's bad mixture bad i cant remember if it's color matched with a possible bad fitment of the intake at the #5,#6 fuel passages.

Ayuh,... If 5,+ 6 were of a lighter color,... That's indicative of them being Leaner....
That could possibly indicate the manifold is leaking on those cylinders...
And, the lack of change when pulling those plugwires says they're not quite Right...

Please keep in touch.

Ayuh,.... I ain't goin' nowhere,.....
I was just waiting for some comments, so you could fill in a few blanks....
'ell,... I've got 3 years invested in you gettin' that barge runnin'... Right....

 

[sarantis]

Re: vibration and overheating at gm 350 (one piece rear seal carburated)

Bond O
I really apreciate your invaluable help ,sometimes i feel even embarased for getting free so much knowledge and experience.I wish i could support iboats by purchasing but the tranportation fee from America to Greece is very high especially when the weight is big.At least i try finalise all my threads to help some other people and when at last repair my boat and find some time i'll start replying in others' simple problems.Again thank you and all the other guys in this wonderfull forum.
"vibration and overheating at gm 350 " to be continued...

 

[dan t.]

Re: vibration and overheating at gm 350 (one piece rear seal carburated)

I very much doubt that you have a problem with the intake. I have put at least 20 old style intakes on new style heads using tapered sleeves on the 4 center bolts and have not had a problem on any of them.# 5 and 6 lean? what is in the hole in the intake runner? it should be plugged or at the most a fitting for a vacume gauge. hooking up a pcv there will make #5 and 6 lean

 

[sarantis]

Re: vibration and overheating at gm 350 (one piece rear seal carburated)

I very much doubt that you have a problem with the intake. I have put at least 20 old style intakes on new style heads using tapered sleeves on the 4 center bolts and have not had a problem on any of them.# 5 and 6 lean? what is in the hole in the intake runner? it should be plugged or at the most a fitting for a vacume gauge. hooking up a pcv there will make #5 and 6 lean

you mean the bolt with the squared head next to the coil? it is there.nothing is hooked up there.if i take apart the manifold will i take any compression so as to compare the#5 AND #6 with the other ones?

 

[CharlieB]

Re: vibration and overheating at gm 350 (one piece rear seal carburated)

I am curious as to this 'new' 5.7 260 block.

Do you know exactly what camshaft is in it?

Did it come with cyl heads installed?

Where they new, or rebuilt, possibly resurfaced?

Milled heads and/or a cam with more duration will raise cranking compression #'s, requiring higher octane rating fuel.


Vibrationwise, I suspect you had to find a newer flywheel to use the newer style couple. Is the new flywheel a 'Marine' part, or used from a salvage yard?

Is it possible that you have a flywheel from an externally balanced 400, instead of from an internally balanced 350?

 

[sarantis]

Re: vibration and overheating at gm 350 (one piece rear seal carburated)

I am curious as to this 'new' 5.7 260 block.

Do you know exactly what camshaft is in it?

Did it come with cyl heads installed?

Where they new, or rebuilt, possibly resurfaced?

Milled heads and/or a cam with more duration will raise cranking compression #'s, requiring higher octane rating fuel.
Vibrationwise, I suspect you had to find a newer flywheel to use the newer style couple. Is the new flywheel a 'Marine' part, or used from a salvage yard?

Is it possible that you have a flywheel from an externally balanced 400, instead of from an internally balanced 350?

I'm curious too.
I don't know what camsaft it has on.
The heads were installed ,they are suposed to be knew but i'm afraid the whole block may be rebuilt although i couldn't distinguish any sign exept the unexpected compression.
The flywheel is that of 350 1piece rear seal for sure.The harmonic balancer is that of my older block 305 2piece but it looked the same with my friends' 350'.
I don't know if these photos can tell you anything.

 

[zbnutcase]

Re: vibration and overheating at gm 350 (one piece rear seal carburated)

As the 400 was discontinued in '80, none were made with the 1 piece seal and small bolt circle so it would be impossible to put one on a 86 or later engine; however, you could put 400 damper on it, which could cause vibration. 'nutcase

 

[dan t.]

Re: vibration and overheating at gm 350 (one piece rear seal carburated)

what are the casting numbers on the heads? in the pictures they look like vortec heads, in that case you would need the proper intake and gaskets

 

[jtybt]

Re: vibration and overheating at gm 350 (one piece rear seal carburated)

Dan beat me to it. Those are vortec heads. They don't have inner intake bolts and aren't torqued to the same specs. Also, they have 64cc combustion chambers instead of 72cc. With flat top pistons that would raise the comp ratio and compression.

There's something wrong here.


...and I would re-check the firing order.

 

[longstand]

Re: vibration and overheating at gm 350 (one piece rear seal carburated)

Sorry to BUT-IN. don't need to reply to my comments.

BUT.. i wish i had all you guys Knowledge.. all the conversion talk. it made me think. hmmm maybe i could do what you guys do with engine.. someday.. iam only 24. i have few years left

 

[sarantis]

Re: vibration and overheating at gm 350 (one piece rear seal carburated)

Dan beat me to it. Those are vortec heads. They don't have inner intake bolts and aren't torqued to the same specs. Also, they have 64cc combustion chambers instead of 72cc. With flat top pistons that would raise the comp ratio and compression.

There's something wrong here.


...and I would re-check the firing order.

Vortec heads?I don't think so.With 6 bolts each side?Maybe the picture isn't so clear .As about the firing order i've rechecked many times.Unfortunately the weather here is awfull and i can't check anything at the moment.i hope in two days time i'll have some news.Thank you all!