Rebuilt, lower compression on new piston - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

Axel18 · 10-24-2013, 10:06 PM

So i sleeved my engine. And i only bought 1 new piston and all rings. The new piston was placed in cyl 1 by the machinist and bored to its size since it was newer than the others. Hence bigger as the skirt was new. All other cylinders were cut to the used pistons.

All Wiseco pistons and rings. Sleeved to 89.5. Reused 3 old pistons but got new rings.

All assembled by a pro.

Did 50 on city, 200kms on a highway and tested compression 150 on all 3 old pistons/cylinders and 130 on the new piston...

Its a KA24 sohc, i had 150 before and its a known good compression on this engine.

Why is the new piston getting lower compression? They are the same model all of them. New rings on all.... all cylinders sleeved and bored to their pistons... im confused. I was told that i have to keep breaking in to get the new piston to its fit.

yetijeff · 10-24-2013, 11:15 PM

All that work and u used mismatched pistons? What do u expect. Is it smoking? Running like shit? Could be a valve train issue as well. Need more info on what exactly happened... Did u get the head rebuilt?

Axel18 · 10-25-2013, 07:29 AM

No, i have wiseco pistons but 1 got damaged by a valve, so i bought a new wiseco one, same model as the other 3, same CR, bore, etc. same model. All 4 pistons are the same, just that one is new the other ones are the ones i had before.

Its running perfectly, no smoking. The head was changed to another one since the last one got damaged along the piston by the valve, the new one got new springs, all valves checked, decked, new seals, valves lapped etc.

yetijeff · 10-25-2013, 05:04 PM

Quote:

Originally Posted by Axel18

No, i have wiseco pistons but 1 got damaged by a valve, so i bought a new wiseco one, same model as the other 3, same CR, bore, etc. same model. All 4 pistons are the same, just that one is new the other ones are the ones i had before.

Its running perfectly, no smoking. The head was changed to another one since the last one got damaged along the piston by the valve, the new one got new springs, all valves checked, decked, new seals, valves lapped etc.

Ok did u use the same model/company's piston rings?... Seems very strange problem your having...

Axel18 · 10-25-2013, 06:38 PM

Yea same piston as the old ones. Wiseco 6587m895.

Im hoping its only a valve guide damaged. Ill do a leakdown test on monday. But yea its pretty weird and im sure everything was installed properly. Unless that the machine shop would have screwed up on fitting the new piston on the sleeve in cyl 1...

Rings were the same 8950xx rings

10-24-2013, 10:06 PM	#1
Axel18 Leaky Injector Join Date: Oct 2007 Location: Miami Age: 37 Posts: 114 Trader Rating: (3) Feedback Score: 3 reviews	Rebuilt, lower compression on new piston So i sleeved my engine. And i only bought 1 new piston and all rings. The new piston was placed in cyl 1 by the machinist and bored to its size since it was newer than the others. Hence bigger as the skirt was new. All other cylinders were cut to the used pistons. All Wiseco pistons and rings. Sleeved to 89.5. Reused 3 old pistons but got new rings. All assembled by a pro. Did 50 on city, 200kms on a highway and tested compression 150 on all 3 old pistons/cylinders and 130 on the new piston... Its a KA24 sohc, i had 150 before and its a known good compression on this engine. Why is the new piston getting lower compression? They are the same model all of them. New rings on all.... all cylinders sleeved and bored to their pistons... im confused. I was told that i have to keep breaking in to get the new piston to its fit.

10-24-2013, 11:15 PM	#2
yetijeff Zilvia Addict Join Date: Sep 2010 Location: Corona Ca Age: 34 Posts: 765 Trader Rating: (3) Feedback Score: 3 reviews	Rebuilt, lower compression on new piston All that work and u used mismatched pistons? What do u expect. Is it smoking? Running like shit? Could be a valve train issue as well. Need more info on what exactly happened... Did u get the head rebuilt?

10-25-2013, 07:29 AM	#3
Axel18 Leaky Injector Join Date: Oct 2007 Location: Miami Age: 37 Posts: 114 Trader Rating: (3) Feedback Score: 3 reviews	No, i have wiseco pistons but 1 got damaged by a valve, so i bought a new wiseco one, same model as the other 3, same CR, bore, etc. same model. All 4 pistons are the same, just that one is new the other ones are the ones i had before. Its running perfectly, no smoking. The head was changed to another one since the last one got damaged along the piston by the valve, the new one got new springs, all valves checked, decked, new seals, valves lapped etc.

10-25-2013, 06:38 PM	#5
Axel18 Leaky Injector Join Date: Oct 2007 Location: Miami Age: 37 Posts: 114 Trader Rating: (3) Feedback Score: 3 reviews	Yea same piston as the old ones. Wiseco 6587m895. Im hoping its only a valve guide damaged. Ill do a leakdown test on monday. But yea its pretty weird and im sure everything was installed properly. Unless that the machine shop would have screwed up on fitting the new piston on the sleeve in cyl 1... Rings were the same 8950xx rings