Boring past .030

[vxtech]

i have read that manufacturer's say not to bore past .030,besides thinner cylinder walls, what other problems does this cause? i pulled the head off my mercruiser inline 6 to check no compression in # 6 cylinder and found all piston tops stamped .060 removed brand new piston found rings siezed to piston, it looks like complete rebuild on motor then it was parked after blowing headgasket (antifreeze in #1) cyl,so with all this being new i was gonna just hone bores &replace all rings on all pistons but will bore being .060 cause durability issue's?

 

[Don S]

Re: Boring past .030

If you are going to say "I read" at least say where you read it so others know. You can read anything you want to read somewhere on the web, but that doesn't make it right. Can I assume THIS is where you "Read" it.
Also, Merc and Volvo doen't even sell rings or pistons for anything over .030.
Most engine rebuilders do a quick .060 bore and max grind on crankshaft so they don't have to buy a lot of different parts or spend too much time checking and doing the job right.
Those engines also don't last very long. And you have one just to prove it.

Why were your rings siezed on one cylinder? Sounds like the .060 overbore has already caused durability issues.

 

[vxtech]

Re: Boring past .030

i read it in another post Don S answered, rings were siezed to piston due to bow up motor down storage-guessing rain water in through carb and gravity seeked out lowest cylinder then entering through open valve rusting rings to piston but just minor surface rust on cylinder wall-wipes away. i had motor running before i removed which it ran good on trailer but no water flow through manifold -guessing that popped head gasket- then checked compression which resulted in me removing engine and investigating no compression on #6

 

[Don S]

Re: Boring past .030

it ran good on trailer but no water flow through manifold -guessing that popped head gasket-

No, that will not "POP" a head gasket. an overheat will, did that happen?
The raw water pump nor the engine circ pump can make enough pressure to blow a head gasket. You have other problems.

 

[vxtech]

Re: Boring past .030

Don S i was using term "pop" meaning when you overheat an engine head gasket fails ,and most of the time forcing combustion gases or pressure which ever you choose into cooling system usually forcing coolant out of radiator cap and into coolant recovery bottle if equipped ,i am guessing previous owner history was newly rebuilt outdrive installed then replaced or rebuilt engine then overheated headgasket failed and now i have aquired vessel , hobby ,project whatever ya wanna call it, exhaust manifold plugged with rust, dirt and every thing else from the bottom =need new manifold that was the one piece that previous owner did not replace

 

[vxtech]

Re: Boring past .030

now aside from being poorly stored ,what other issues does .060 ? or should i search for used block only requiring .010 rebore and put my .010 crank and .010 rods in?

 

[79Glastron]

Re: Boring past .030

A large over bored on an engine like that could result in overheating issues due to thin cylinder walls. You could sleeve the block back to standard, but that probably won't be cost effective. A better option would be to find a new block and keep your rotating assembly if a problem occurs.

 

[chiefalen]

Re: Boring past .030

What kinda motor and what vintage are we talking about?

 

[chiefalen]

Re: Boring past .030

Who said bow up out drive down is the incorrect way to store a boat?

Can you put a copy and paste original post here.

 

[Bondo]

Re: Boring past .030

,what other issues does .060 ?

Ayuh,...

What it means is,...
Once you've torn it down,...
Hone the rust out of the cylinders...
Now Measure them...
If by some chance they're Not out of Spec.... Put it back together with fresh parts....
But,...
They'll more likely be out of Round, or Egg shaped... Then you'll need another Block,..
As the 1 you have has already been bored beyond any hope of running again...

 

[vxtech]

Re: Boring past .030

Chief - bow up motor down storage is correct if you leave engine cover on and spark arrestor on as previous owner did not for some period of time(short period) and carb became funnel for rain water on this 1975 chaparral 21.6 inline 6 mercruiser (gm 250)

 

[vxtech]

Re: Boring past .030

79 Glastron- so cooling temp may increase due to thinner walls if cooling is not up to par which will then lead overheating & preignition ? but if cooling is adequate temp should rise slightly above stock bore block ?

 

[Maclin]

Re: Boring past .030

It is not so much that the cooling system outside the block would get outpaced, it is more about what happens to the coolant inside the block as it circulates. The thinner walls make for less heat sink action. Water needs a little time to draw out the heat and with hot spots like that it cannot keep up and temp spikes in those places. The cylinders then have hot spots and it escalates from there.

 

[rodbolt]

Re: Boring past .030

.060 on that old chevy inline block is fine. we did it quite a bit.
have the block PROFESSIONALLY honed then checked for serviceabilty.
DO NOT use a drill mounted set of stones or a dingle berry hone.
have it done correctly then check the bores for correct size and roundness and taper.
siezed rings are normally a sign of incorrect assy.
normally an incorrect end gap or rust in the cylinders then an attempt to run it.
but even with NO rings you should have had some compression.
check the rest of the engine for damage as well.

 

[vxtech]

Re: Boring past .030

Rodbolt- i had compression on number 6 cylinder only when i kept juicing cylinder with oil then i would get 45 psi with oil in cylinder which led me to remove and diassemble to find block had all new internals already inside it was that rain water went in through carb rusting rings to piston, rust on cylinder wall literally wiped away with rag and brakeclean, lots of pb blaster on rings and tapping with wood block i was finally able to free rings , ithink the guy i got it from just got tired of putting money in it after replacing outdrive then rebuilding engine ,overheated motor =head gasket failed manifold clogged up then poor storage led to rings rusting to piston

 

[chiefalen]

Re: Boring past .030

Rodbolt: Yes they used to bore out to the max in auto L6's.

I know i had a 71 nova, L6. And a 76' nova L6.

But what rpms was i turning? 1500-2000 ?

Not no 4600 rpms.

Also i wasn't running the car in salt water, and using it for cooling the motor, what you think the cooling jacket looks like?

In cars we use anti-freeze. Ain't rusting the block.

Rust alone makes it harder to cool the block.

Not that i turn that now, i only go wot for a minute or 2 till i test for the right prop and such.

And then i stay at 3000-3500 leave the extra rpm to get out of the way of the giant tankers and dredgers, or sea ferries all over the bay.

These are old motors, and as i have posted before, these ole girls got to be treated right or your gonna be needing a new motor.

I wasn't gonna stick my 2 cents in cause the other guys are handling it fine.

Op you check the mating surface, with the head real real good?

What i mean get a "magnafiglass"<spelled wrong.

Go over the surface real, real, good. See any hairline cracks, between the cyl. and cooling holes, bolt holes, or sides.

Check the corner holes most. The hole pulled up from a bolt, look on the sides good.

See a painted over crack?

Same with the head, see a hairline crack? Go over it real good.

Maybe you wont see it with the naked eye.

 

[rodbolt]

Re: Boring past .030

trust me,.060 on that block is acceptable.
we raced them at 6200 RPM in both the 250 CID and the 292 CID and a few hybrid versions of the two inline 6's.
and if you read what I posted I did say to get the block PROFESSIONALLY inspected.
most proffesionals will correctly hone the block and magnaflux the deck and bore area.
cause trust me, without a correct honing the rings will finnish scraping off the rust and that rust will pack into ring grooves and imbed itself in the soft metal bearings.
I am actually probably one of the few posters here that has actually run a crank grinder,a blanchard grinder or a valve facing machine or even a hard seat grinder.
I know I have built more engines than quite a few have seen.
biggest problem we have now is finding a competent machine shop.
back when I was grinding cranks we would chamfer the oil holes and cut the correct radius on the journals, last crank I saw done all the shop did was grind it.
I found it after tearing it back down cause the sharp oil passasges tore up the new bearings.
best thing I can tell a do it yourselfer and even most so called techs is to purchase a copy of Motors Auto Engines and Electrical Systems.
library of congress 77-88821, ISBN0-910992-73-8 copyright 1977.
will explain in detail how to prep and check the various mechanical systems on an articulated rod automotive type engine.
as long as the block,crank,rods and deck surfaces are proffesionally done a monky can pretty much assemble an engine that will go 100K plus miles.
the key is the prep work has to be meticulous and the assembly work kept clean.

 

[chiefalen]

Re: Boring past .030

Rodbolt: Hope you did not take offense, and i didn't see the pro. part.

Maybe when my motor goes i'll drive it over to you. Than i'll know it'll get done ''right''.

 

[Bondo]

Re: Boring past .030

What i mean get a "magnafiglass"<spelled wrong.

Ayuh,....

Al,... Here's the Cure for that,....

 

[chiefalen]

Re: Boring past .030

I have firefox tells me it spelled wrong, but not the correct spelling.