The Stovebolt Site Forums The Shop Area Engine Shop 250ci chevy cylinder 1 egging

whats up guys im mike, still pretty new to this forum though ive tried searching the topic because im not new to forums in general lool.. couldnt find enough information so here we are. first of all i have a theory as to why this happens with these engines. im talking of course about cylinder #1 going out of round at the upper section right behind the water pump.

from what i can tell every other cylinder is wearing evenly in both of these 250's ive torn apart so far.

one is a pre 75 non emissions that had been at least taken apart and freshened up at one point from what i could tell by the gasket maker and the driver side cracked head bolt hole behind water pump indicating he should have used head studs lol.

other one is a 1979 integral with a clearly longer service life with some possible neglection as well but overall not terrible for 80 dollars.

both engines seemed to show even cylinder wear on cylinders 2-6 but the same type of tapered wear focused mostly on the area directly behind the top of the water pump impeller. from what ive read people claim the number 1 cylinder runs hotter than the other 5 and im not so sure thats the case.
with even wear on every other cylinder that would indicate a consistent temperature change throught the entire cylinder allowing for evenly dispersed slow enough for safe expansion and contraction. with the water pump pumping cooled water directly onto that upper portion of the cylinder wall it causes that upper portion of the cylinder to not expand to quite the tolerances as the rest of the cylinder promoting increased friction and wear inevitably egging the cylinder out.

this is my theory and im more than ready to entertain any other ideas or findings on the matter. i dont yet have any exact measurements, i need a good, painless, and accurate bore gauge for about 50-60 dollars or less as long as its a good product! but i am concerned about this problem because on the 79 integral motor the edge created from the wear appears to be close to .030 deep and the engine appears to be completely standard. it just sucks i got that other engine that looks beautiful inside, and the block is cracked.. i just hope the 79 block is useable because though the engine may come cheap its still annoying to have to find another engine for the right price in hopes its unmolested and rebuildable.. any insight is greatly appreciated and entertained.

You have put a lot of thought in this. I have been at this for 60 years & have found #1 cyl. wears more then the rest on practically all engines. I don't know why. Maybe Hot Rod Lincoln will chime in. He has a lot of theories. The crack in the block has been a problem around the front head bolt on the drivers side. The factory has revised the torque specks to 85 lbs. on that particular bolt.

This theory has been around awhile, there is nothing that can be done about it.

Look for a 292, that will solve the cooling issue of #1 cylinder, at least the top of the bore issue's.

Joe

The number one cylinder has always been the one to show wear in our Cummins Diesels. And this is a history that spans 50 years and as many as 20 trucks running at a time. We have always attributed it to the fact the number one cylinder is the last to get oil. If bearings and cam bushings start getting excessive clearance, the no one just doesn't get enough oil. We recently lost a N14 due to a run away and it was the number one rod that spun. I also have an ISM in the shop right now that is a high miler and it is the number one that is low compression due to blowby. We didn't bother to mike the bore because we installed 6 piston packs that come with wet sleeves. No engineer has ever told me that this is the reason, but all of the old time mechanics that I have known over the past 60 years pretty much shared the theory.

the place that will wear out of spec the fastest is the place that the temperature fluctuates rapidly most often. its clear there wasnt much thought put into the design of the water pump jacket in terms of directing the flow of cold water a little bit smarter... so you say the 292's dont have this issue? is it the water pump that sets them apart or is the water pump housing designed differently?

id like to stick with the 250 if i can as im already strapped for space as it is with that s10 so im in no hurry to switch to the 292... BUT, i want a reliable engine that wont lose compression on that #1 cylinder while every other cylinder wears within a limit leaving me with a lousy engine after possibly only 1/3 of its potential service life... has there been any tricks to redirect the water? or possibly even a secret thermostat, rad, and e-fan set up to keep temps as consistent as possible?

what cummins engines are you speaking of? generally the first slug to see lube is the one closest to the oil pump and generally the oil pump is an accessory driven at the front of the engine somehow. generally if its an oiling issue you will have scoring rather than excessive taper.

forgive me, i missed where you said n14. so wait, how did the engine run away from a spun rod? or are you saying that was the result of the runaway? what exactly caused the runaway?

also, may i ask where you learned #1 cylinder is oiled last?

I know the number 1 cylinder on my 230 had a "bump" in the front of the cylinder wall. We figured it was caused by someone trying to install to long of a bolt in the water pump at so time. Anyway my uncle used a ridge reamer and cut the bump out and the engine was reassembled. Still running good yet today.

John

The cold water theory has been around forever and couldn't be more incorrect. True, all the 230 and 250 engines always seem to have excessive wear in the front cylinder. We raced them for 25+ years and have consulted with top GM engineers back in the 80's about this problem and what was told to us was this. It comes from a "green" cast block, coupled with the fact that the front cylinder inside the water jacket is machined for the water pump impeller causing the cylinder to "relax" or stress, and not stay round. This along with a short head bolt on the driver side deck, fails to correctly pull the cylinder round and hold tension as time passes. Its like when you only machine one side of a piece of steel and it curls like a banana, this is what happens to the cylinder when only the front face is machined for the impeller clearance, plus it is now much thinner than the rest of the cylinder in the front portion. After a block becomes seasoned and is rebuilt years later, it will not do this anymore, or at a minimum unless the front head bolt issue is resolved, and then all 6 cylinder will wear more evenly.

I've encountered this problem on two 250's, and the fix can be pretty simple. Bore the block for a 1/8" wall sleeve in the #1 cylinder, and machine the water pump impeller back just enough that there is no interference with the sleeve, in case it rounds out the part of the cylinder where the milling was done. We also did something similar on Ford 2300 OHC 4 cylinder engines when boring them out .110" for 307 Chevy pistons. The front cylinder ended up paper thin where the pump impeller machining was done, so we always sleeved that hole first and bobbed the impeller for clearance.
Jerry

Dang Jerry, that's some high tech stuff there! I always pay attention when you chime in, but man you know your stuff.

Thanks, Carl! Those little 2300's sounded like a bumblebee on steroids at 9500 RPM on a 1/4 mile dirt track! We ran them in the "Outlaw Mini-Stock" class in Pinto and Mustang II bodies.
Jerry

Ennjunz, this is getting way off topic, but the N14 broke a shaft in the turbo, which is not commons, but it happens when you log several million miles a year. Although the driver had been driving a truck for over 20 years, he had never heard of a runaway. With a broken shaft the turbo sprayed oil into the intake and that created the runaway. With all the smoke, the driver thought something was on fire and called the fire department instead of putting it in Hi gear and dumping the clutch. The engine ran until it was out of oil, the No.1 spun, the rod stretched and the piston hit he head. They say bad luck runs in 3's. We actually blew 3 turbos in 2013 and they all were Cummins Recon. Not some of the Chinese aftermarket that are around now.

I just have to ask...
I hope your not referring this many miles for one engine, because that is mathematically impossible.

When the guy owns several dozen trucks, it's very possible- - - - -gotta know the players around here before you start questioning their statements!
Jerry

Didn't this all start out as "how dependable is the 250," kind of?
While it is probably nowhere as well designed as some of the modern engines or most race engines, but it is well designed enough that a stock, well used 250, under my abusive driving style, went from 150k to 326k when I sold it. The new owner put another 80k on it before it started to get really tired. And I have it back! I had already planned to do what Jerry suggests when I have the block bored.
The point is the 250 is good enough to go 400k if you keep oil in it and keep it reasonably cool. It isn't a big, shiney powerhouse, but it is the modern essence of the STOVEBOLT engine! Dang things run forever!

keep on truckin'

Les

thats good to hear. the engine pre 75 was said to have 140,000 on it and the cylinders were worn in maybe .005 throughout the stroke with a minor amount of taper on cylinder one as opposed to the 79's cylinder 1, so i can imagine the 79 integral motor with significant taper on cylinder one had a mass amount of miles.

i will know whether i can use the block or not once this eastwood tools bore gauge arrives in mail. i feel ill be able to salvage it and run .060 over but ive read that is stepping into the realm of cooling problems? ive also heard of people getting away with .125 over so i dont know what to think.

i can see how a freshly cast block would promote that type of wear compared to a seasoned block thats seen so many heat cycles so feel confident in being able to build a strong 200k+ engine out of this 250. im very excited to see how well it performs in this s10 with a 700r4 behind it.

if theres any mpg/economy gurus on these 250's please feel free to share any valuable information you may have!

Going to .060" over is pushing things a little. I'd very much prefer .040 over if that's an option. Definitely consider sleeving #1 if it's got more taper wear than the other cylinders, even if you only go with the thinwall 3/32" sleeve. One sneaky trick is to use 307 V8 pistons- - - -they're flattops instead of the 1/4" dish top that the 250 piston has, and every other dimension is the same, bore size, compression height, wrist pin diameter and weight. I've also milled the head on a 250 engine .050" without having any piston/valve interference problems. With the flattop pistons and a milled head, the engine really comes alive.
Jerry

Hey Hotrod, all this modification stuff is off topic. And besides that you are polluting my mind with ideas of pursuing new avenues of adventure,for which I have neither the time nor the funds.
Carl

Who, me- - - - -an enabler? Perish the thought!

Jerry

I was going to suggest the 307 pistons also, its a cheap way to increase the compression about 1 point. Just be sure the pistons you get a true flat top, not the generic replacements. Some have a chamfer around the top along with four valve reliefs. This one modification would do more for mpg then any other thing you can do.

Joe