4A-GE Excessive Blowby 3000km after Rebuild

[ballpencil]

I'm prepared to hear the worst..

I just had my smallport 4A-GE rebuilt with new piston rings. It was already 0.50 overbore when i had it rebuild and according to the machine shop, i just need new rings.

Rebuild was 2000-3000km ago, no oil change yet since rebuild.

The first time i ran the engine on high RPMs was when it was around 1000km and i found oil all over the bonnet, coming from the dipstick hole. The engine still ran great though. I put some sealing tape on the dipstick to help prevent this again.

Last night at about 3000km old, i took the engine for its second high RPM run and again oil was splattered all over the engine bay, still coming from the dipstick. I can feel excessive blow-by coming from the dipstick hole and cam cover breather. Now the engine is running limp.. However, i think no oil is being burned as i found no oil smoke from the exhaust.

I changed to new plugs and still limping. Sticky injectors are unlikely. So could it mean that the limp is from compression leak, hence blow-by?

1. Can a compression leak happen without any oil burnt as no oil smoke is found from the exhaust? I thought leaky compression = oil escaping to combustion chamber = burned oil = white smoke from exhaust?
2. Why limping after 3000km? I thought the rings should bed properly by now?
3. What should i do?

I'm somewhat okay if i have to rebuild the engine again as i need to put low comp pistons for turbo anyway. I just want to prevent the same thing from happening after the second rebuild.

[Xauterus]

Hello
Did you use running in oil when you built the motor? When you say you ran the engine on high rpms. How high? I find it better to drive the motor how you built it but keep the rpms down for the first 1000km. By that i mean drive it hard but not too high rpm. Keep varying the speed. It does sound like you have glazed the bore. Were the rings installed correctly? Gapped? Oil ring installed correctly?

[thechuckster]

... and did you have some kind of crankcase ventilation system? from memory the 4age have a small vacuum line that runs from cam covers to intake plenum?

but massive amounts of blowby does suggest the rings are borked - either from a poor run-in or glazing of the bores (where they honed by the workshop that re-ringed it?)

A wet & dry compression test might help indicate whether the rings are not sealing - tho if they're still fairly stiff (from being barely used) it might not show up.

[ballpencil]

Ummm... no i didn't use any running in oil. I'm still using the same oil used just after the rebuild. High RPMs: 5000-6000 RPM. Did i do anything wrong? Incorrect break-in procedure?

I had the rings installed by a mechanic so i can't really say if they were done correctly.

Glazed the bore: a thin film of oil forming on the bore causing the ring to skate. The only remedy is to rehone the cylinders? As i said, i prefer not to oversize as my low comp GZE pistons are also 0.50 OS. Is it likely i have to oversize? Or simply rehoning would suffice?

[ballpencil]

... and did you have some kind of crankcase ventilation system? from memory the 4age have a small vacuum line that runs from cam covers to intake plenum?

yes, i still have the PCV system running.

where they honed by the workshop that re-ringed it?

yikes.. must honing be done even if no oversizing is done? i mean, they just swap the rings with new ones and put the pistons back. nothing was done to the cylinders besides measuring and deciding that oversize is not needed.

is it still possible for me to put low comp GZE pistons of the same oversize? if it's glazing, it's simply rehoning and swapping the pistons, right? can i reuse the rings, considering they're barely used?

[thechuckster]

not even a quick hone with one of these?


shit, I would of, particularly if the existing rings were stuffed.

And yes is same size, yes rehone and swap the pistons, no don't re-use rings.

[fixeruperer]

the problem is in the machining or the way it was put together.
running in oil, id just use a cheap mineral base oil with no fiction modifiers.
my 4ag's have a hard break in (hard run in for about 300ks then to the dyno for a power tune) and the oil breather vent straight to a catch can, i have never ever found oil in the catch can.


hone should be done when ever the cross hatch looks weak, if the pistons are out, it never hurts to give the bores a quick hone.
glazing is done with the rings to bores, the pistons should never touch the bores, if they do you have awesome problems. re measure the pistons and bores and make sure they are in spec (they are not forged pistons so make sure you have the correct piston to bore clearance . re ring and hone them cylinders.

[ballpencil]

ummm.. what about this?

1. Can a compression leak happen without any oil burnt as no oil smoke is found from the exhaust? I thought leaky compression = oil escaping to combustion chamber = burned oil = white smoke from exhaust? --> just for the sake of knowledge enrichening.
2. Why limping after 3000km? I thought the rings should bed properly by now? (considering it was running great before the second high RPM run).

[TERRA Operative]

If you didn't hone the bores, that will be the problem.
Pull the engine down, get the bores honed, and follow this guide to breaking in, to the letter.

Break In Secrets--How To Break In New Motorcycle and Car Engines For More Power

I've used it myself a number of times and I always end up with rev happy engines with minimal(!) blowby.

[fixeruperer]

compression leaks past the rings (compression rings), into the sump and out of, well anywhere it can e.g dipstick tube. when all the rings are worn (old engine), the oil doesnt get scrapped correctly and passes onto the top of the piston and get burnt through ignition.


have you got an oil pressure gauge, you can check what oil pressure your running ?

there's no break in secrets, just theories .

[TERRA Operative]

Well, the theory I linked to works pretty damn well......

[fixeruperer]

thats what they all say

[thechuckster]

The first time i ran the engine on high RPMs was when it was around 1000km and i found oil all over the bonnet,

that probably didn't help if you were babying the engine for the first 1000ks - I won't buy into a debate about running-in best practice but I'd say the combination of no bore hone and light loads/rpm during running has either glazed the bores or the rings have never seated into the bore and are thus allowing way too much blowby.

re your query:

. Can a compression leak happen without any oil burnt as no oil smoke is found from the exhaust? I thought leaky compression = oil escaping to combustion chamber = burned oil = white smoke from exhaust? --> just for the sake of knowledge enrichening.

yes, as fixeruperer has inferred, if the rings are not sealing but still have significant amounts of tension in them, they will allow combustion gasses to get past them but will scrape most of the oil off the bores. So you get excess blowby but not oil burning.

Rules of thumb for diagnosis of exhaust smoke:
- blue/white on startup when cold - leaky valve stem seals
- blue/white smoke when accelerating or under significant load - rings fubar
- blue/white smoke during high rpm deceleration - valve stems seals
- white smoke when warm (and missing when idling) - BHG into coolant gallery
- blue/white smoke all the time - motor fucked, replace with 1/2JZ
- blue/grey smoke under bonnet - engine fire

[andrew_mx83]

Rebuild was 2000-3000km ago, no oil change yet since rebuild.

whoa horsey!!! the first lot of oil should be in for about 300km not 3000!!!


my run-in method:
running in oil
drive the nuts off it, keeping revs under about 3/4 of redline -lots of load (either up hill or in top gear at low speed), lots of engine braking
dont baby it, dont let it idle
drain running in oil after 500km max, replace with a full mineral oil.
retorque head
engine is pretty much run in now unless it was built very tight. still keep revs down for the first 1000km then go nuts


just heard back yesterday from a customer a built a 7m-gte for recently -above method used for run-in.... he is amazed as its the first turbo car he has seen which doesnt fill up the catch can with oil, not a drop! those rings are already sealing 100%, its probably only got a handful of hours on it too.

[SHEPPO3930]

time to pull it apart, hone the bores, and put a new set of rings in it.

then run it in properly this time!