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!

 

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.

 

Isn't there already a groove since it is already leaking? Is it small enough that new rings will seal it? If compression test with a capful of oil seals compression, then is it salvageable? And what piston/rod/rings are good replacements?

 

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.

 

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?).

 

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.

 

Some must have done it on their own. Has anyone been successful? And if not successful, what failed?

 

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.

 

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?

 

This is a good idea. I can have a machine shop check my block to make sure everything is healthy while pistons are out.

 

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.

 

 

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?

 

you messed up assembly. sorry.

 

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.