Risk with running engines with 1 or 2 low compression cylinders
#1
Risk with running engines with 1 or 2 low compression cylinders
There seems to be many evos with 1 or 2 cylinders with low compression. What are the risk of running them (if the engine makes power, why fix it right?)?
And to fix them properly, does the block need honing? Realistically, I think most will want to rebuild their bottom end to handle 500-550 ft-lbs of torque.
I would think that if people get low compression and fix early, they will save block and maybe head. If running with low compression too long, wouldn't that cause cylinder wall to wear more?
Has anyone continue to run with low compressions? Any problems? The rest that fixed rings, what exactly was replaced, cost of repairs/upgrade, and did it hold up long? Thanks!
And to fix them properly, does the block need honing? Realistically, I think most will want to rebuild their bottom end to handle 500-550 ft-lbs of torque.
I would think that if people get low compression and fix early, they will save block and maybe head. If running with low compression too long, wouldn't that cause cylinder wall to wear more?
Has anyone continue to run with low compressions? Any problems? The rest that fixed rings, what exactly was replaced, cost of repairs/upgrade, and did it hold up long? Thanks!
#2
Account Disabled
If you fix it straight away, it's easy and cheap.
Just replace the piston / rod assembly.
If you keep driving it, you'll end up with a groove in the bore .
That's NOT and easy cheap fix.
I've stripped and measured hundreds of engines in all sorts of states with all sorts of abuse.
Just replace the piston / rod assembly.
If you keep driving it, you'll end up with a groove in the bore .
That's NOT and easy cheap fix.
I've stripped and measured hundreds of engines in all sorts of states with all sorts of abuse.
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2006EvoIXer (Mar 18, 2018)
#3
If you fix it straight away, it's easy and cheap.
Just replace the piston / rod assembly.
If you keep driving it, you'll end up with a groove in the bore .
That's NOT and easy cheap fix.
I've stripped and measured hundreds of engines in all sorts of states with all sorts of abuse.
Just replace the piston / rod assembly.
If you keep driving it, you'll end up with a groove in the bore .
That's NOT and easy cheap fix.
I've stripped and measured hundreds of engines in all sorts of states with all sorts of abuse.
Last edited by 2006EvoIXer; Mar 18, 2018 at 01:13 PM.
#4
Also, if someone is going to replace rings, shouldn't they go ahead and replace pistons and rods at same time so engine can handle more power? Which are the combinations that people have done and have reliable engine? I hate seeing "upgrades" that just doesn't last or run right like OEM.
#5
I've heard of many evos making 500+whp on stock bottom end but rarely hear of failures. I know someone who made 700whp with torque tuned down to low 400s. It didn't last long. I'm wonder if bottom end should be upgraded as an insurance measure since a rod can destroy entire engine. Since most people will have their heads off for valve springs and head studs upgrade, this would be the time to upgrade bottom end (only pistons and rods?).
#6
EvoM Community Team Leader
i think its pretty well established that ~400ft-lbs is the most torque you want to run on a stock bottom end. The problem with doing a whole bottom end is there is just so much involved. The chance of something getting screwed up in some intermediate stage is pretty high. Thats why people are paying tons of money to ship their engines around the country, just to improve the odds they will have a quality piece in the end.
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2006EvoIXer (Mar 18, 2018)
#7
i think its pretty well established that ~400ft-lbs is the most torque you want to run on a stock bottom end. The problem with doing a whole bottom end is there is just so much involved. The chance of something getting screwed up in some intermediate stage is pretty high. Thats why people are paying tons of money to ship their engines around the country, just to improve the odds they will have a quality piece in the end.
Last edited by 2006EvoIXer; Mar 18, 2018 at 11:33 AM.
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#8
Evolved Member
Lots of people assemble engines. I've assembled engines. The trick is to have a good machine shop measure and fit the parts - the emphasis is on good here, shop around and ask questions. Read a couple of books on engine building, buy an engine stand and off you go.
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2006EvoIXer (Mar 18, 2018)
#9
I'm tempted to build my bottom end but don't want to make things worse after dumping more money into my car. I just want to change my rods and pistons and not touch my crank and bearings. I think I can unbolt the rods from crank and pull them out on top. Installing new pistons will probably only go in from top. Are there tested combinations of pistons/rings/rods that has held up reliably?
Last edited by 2006EvoIXer; Mar 18, 2018 at 04:40 PM.
#11
I know this sounds crazy to do to my engine with 61k miles. I just cringe when I think about rods letting go and destroying block, head, and maybe containing oil that can get into every bearing (including turbo, oil cooler, rocker arm bearings, lifters, etc). After a catastrophic failure, it will be very hard (and expensive) to get the engine to run right again.
#12
I did a stupid thing.
engine in chassis, pulled pan/pulled head and all, fitted new manley rods and pistons, rings and bearings, stock bore, used flex hone to hatch cylinders, all was ok, except...
after not only 550miles of under 4500rpm (virtually no boost) I just barley stepped into it and then spun rod bearing...ffs
I checked them all with plasti gauge and removed it before sending it, must have been some**** in my oil galley.
needless to say, one rod needs machined or replaced, crank needs redone or replaced and of course go theough entire engine and go from there...
ran beautifully during the 550miles break in...
but lesson learned.
engine in chassis, pulled pan/pulled head and all, fitted new manley rods and pistons, rings and bearings, stock bore, used flex hone to hatch cylinders, all was ok, except...
after not only 550miles of under 4500rpm (virtually no boost) I just barley stepped into it and then spun rod bearing...ffs
I checked them all with plasti gauge and removed it before sending it, must have been some**** in my oil galley.
needless to say, one rod needs machined or replaced, crank needs redone or replaced and of course go theough entire engine and go from there...
ran beautifully during the 550miles break in...
but lesson learned.
#13
Wow, that totally sucks!
Do you think it was dust from the flex honing? Where else could you have gotten debris to plug up your oil galley?
Do you think it was dust from the flex honing? Where else could you have gotten debris to plug up your oil galley?
I did a stupid thing.
engine in chassis, pulled pan/pulled head and all, fitted new manley rods and pistons, rings and bearings, stock bore, used flex hone to hatch cylinders, all was ok, except...
after not only 550miles of under 4500rpm (virtually no boost) I just barley stepped into it and then spun rod bearing...ffs
I checked them all with plasti gauge and removed it before sending it, must have been some**** in my oil galley.
needless to say, one rod needs machined or replaced, crank needs redone or replaced and of course go theough entire engine and go from there...
ran beautifully during the 550miles break in...
but lesson learned.
engine in chassis, pulled pan/pulled head and all, fitted new manley rods and pistons, rings and bearings, stock bore, used flex hone to hatch cylinders, all was ok, except...
after not only 550miles of under 4500rpm (virtually no boost) I just barley stepped into it and then spun rod bearing...ffs
I checked them all with plasti gauge and removed it before sending it, must have been some**** in my oil galley.
needless to say, one rod needs machined or replaced, crank needs redone or replaced and of course go theough entire engine and go from there...
ran beautifully during the 550miles break in...
but lesson learned.
#14
Evolving Member
iTrader: (1)
I did a stupid thing.
engine in chassis, pulled pan/pulled head and all, fitted new manley rods and pistons, rings and bearings, stock bore, used flex hone to hatch cylinders, all was ok, except...
after not only 550miles of under 4500rpm (virtually no boost) I just barley stepped into it and then spun rod bearing...ffs
I checked them all with plasti gauge and removed it before sending it, must have been some**** in my oil galley.
needless to say, one rod needs machined or replaced, crank needs redone or replaced and of course go theough entire engine and go from there...
ran beautifully during the 550miles break in...
but lesson learned.
engine in chassis, pulled pan/pulled head and all, fitted new manley rods and pistons, rings and bearings, stock bore, used flex hone to hatch cylinders, all was ok, except...
after not only 550miles of under 4500rpm (virtually no boost) I just barley stepped into it and then spun rod bearing...ffs
I checked them all with plasti gauge and removed it before sending it, must have been some**** in my oil galley.
needless to say, one rod needs machined or replaced, crank needs redone or replaced and of course go theough entire engine and go from there...
ran beautifully during the 550miles break in...
but lesson learned.
#15
Evolving Member
iTrader: (1)
original topic; i had a friend that ran heads up nitrous (377 sbc but ice is ice) and went just as fast with one cylinder at 95% leakdown.
it depends on why it has low compression.
slamming together short blocks isnt too bad, just need some patience and keep it clean. whenever i help friends i enforce the rule that if they wont eat off it, its not clean enough yet.
it depends on why it has low compression.
slamming together short blocks isnt too bad, just need some patience and keep it clean. whenever i help friends i enforce the rule that if they wont eat off it, its not clean enough yet.
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2006EvoIXer (Mar 18, 2018)