compression result how bad is this???

[M-type]

She said the car had some overheating issues. Do you see any white smoke when you fire it up. It is normal at this time of year to have the translucent steam from the tailpipe, but white smoke will indicate burning coolant, i.e. head gasket. Another way to tell the difference is the exhaust fumes should smell very sweet, almost like a sour candy kind of smell.

also the bleeder screw on corner of intake plenum is hissing at temp

[nelsonmxmarc]

It's pretty irrelevant at this point. The numbers speak for themselves..

Seals? There are only rings on the piston, seal would be your headgasket or valves, but i would point more towards rings as theres a rather large discrepency across the board..

Whether you convert to bar or psi, either way you look at it, the top end needs a proper leak down test and needs the proper work; hone and rings may not be enough, i would suggest bore, sleeve, pistons, rings, stainless headgasket, arp headstuds (never reuse headstuds), have the head cleaned, valves cleans and head decked.. replace. Bottom end should be solid, and now top end will be refreshed.

[M-type]

It's pretty irrelevant at this point. The numbers speak for themselves..

Seals? There are only rings on the piston, seal would be your headgasket or valves, but i would point more towards rings as theres a rather large discrepency across the board..

Whether you convert to bar or psi, either way you look at it, the top end needs a proper leak down test and needs the proper work; hone and rings may not be enough, i would suggest bore, sleeve, pistons, rings, stainless headgasket, arp headstuds (never reuse headstuds), have the head cleaned, valves cleans and head decked.. replace. Bottom end should be solid, and now top end will be refreshed.

thank you ... will test and post tomorrow

[TW]

Not good.

Compression is a bit of a shady topic because it leads to so many sub-categories of issues and possible causes..

The obvious ones are ring wear and are the most common for a stock motor/build as it's not subject to high boost, meaning the headgasket should still be in top shape.

The other can be as i just said, the head gasket. If it's leaking, you'll be running through a bit of coolant that's escaping the galleries and will notice it going down / puffing white smoke is also a good indicator. (At this temp it will be hard to tell, but smell the moisture at the tip, it will smell like burnt coolant)

Lastly you'll be looking valve seats. If the valves are nice and dirty, it could be they're sticking open a bit allowing air to escape. This isn't THAT common but still viable as an excuse for low compression.
There are a few 'cleaning' additives/machines like Motorvac that clear out gunk, but on old used up valves/guides/seats, it could cause more harm than none if the debris is severe.

In this case, your best bet would be to have a leak down test. Now correct me if i'm wrong because i've yet to do one, but it will discount the data of the rings, and pinpoint head and valve seep, whereas a typical compression test that monitors compression on each bore will account for ring wear however discounting hg and valves (although these will have an affect). Basic hypothesis here is that the normal-standard issue compression test doesnt discount much, it gives you a number.

Marc,
compression test will indicate the overall compression of the cylinder. This will include ring, headgasket, and head (valve) sealage.
leakdown test will specify where the leak is happening, either by the rings (out the pcv valve), the headgasket, the intake valves (air out the plenum), or exhaust vales (air out the exhaust, theoretically). ring sealage is indeed a factor in the leakdown test.

[bellis_GTR]

a friend of mine wrote on his wall ( facebook) that there was a nice impul 4door ar her job LOLL I'm sure it was you.

Hahaha when I saw that, I thought of M-type's sig

[M-type]

nissan claims they dont have the ability the preform a leakdown test anymore
so unable to test
i said isnt it just some oil in the cyl and a another compression test to see if the compression is the same or higher

[M-type]

then again he thought it had 63,000 miles not kilometers
so maybe the tech will shake his head and go okay its not carbon build up then... duh?!!
then they said yea but its 20 yrs old
no it 16 yrs old and driven only 7-8 months a yr(on weekends) so like 6 years worth of driving
if i had more time tools money and a walk through id do it all myself
but i dont and my garage floor is on a angle so no jacks stands

north american techs are just so used to working on **** held together with hope and dreams
that my compression test looked fine to them a little carbon build up maybe
and no overheating issue,,,,, but if i blow a gasket 5 miles down the road they say not there fault

AAAAGGGGHHHHH

this winter im fuckin making it perfect come HELL or high water i sick of fcukin broken cars

[cschepp]

Listen man I can understa d your frustration but the only way you know it's perfect is if you do it yourself. I have owned my car for 5 years now and it has spent just over half of it in a shop being worked on. Once I'm done with it will be one hell of a car. Doing it yourself will save you money and help you learn things along the way.

[Skym]

Compression test with oil is a wet compression test. It checks if ring seal is the cause. Valves do leak on RB head (seen test results of RB20DET head), but one cylinder should be down in compression more than the rest of them (120 cylinder for example). If compression is low on 5th and 6th cylinder, it's headgasket. Around 5th and 6th is where the headgasket usually lets go, due to where engine gets the hottest (common on any straight 6 engine, as is closest to firewall where heat builds up, etc). The result is head warps and crushes headgasket, breaks seal around cylinder. Also is where the exhaust manifold can leak and make engine go lean. If low compression on all cylinders or 0 compression on one cylinder (cylinder 1 on one RB20DET I know of), then rings (could be valve, but very rare).

Compression probably won't be even across cylinders. As far as I know they don't check the volume of domes in head at factory (use water, plastic plate, tube with marks on it), correct them via skimming head, etc to even them out. It's done when engine is rebuilt. Quite common process on high hp V8's. Also helps with ECU tuning, as all cylinders are even.

It's best to find the cause of low compression, could be lack of changing coolant or thermostat sticking closed, overpressurising cooling system and headgasket leaking, overheating in the past that caused head to warp, crush headgasket, ECU tune, lack of fuel with lost rings. Most of the time it's lack of maintenance, thrashing engine or modding engine incorrectly.

[CelicaKidd_205]

I think your frustrations with the Nissan tech has more to do with lack of resources than a lack of overall knowledge. Remember, Nissan North America has never touched an RB motor, they will not have any parts or specifications listings in any of there databases. Theoretically the only way they can get that stuff is by talking to people from Nissan Japan, and you can only guess the time/effort it would take for them to do that. If you ask me you'd be much better off finding spec sheets and part listings yourself and bringing it to an independent garage who will be much more ready to deal with an oddball car because they have to deal with many more makes/models compared to a dealer.

[nelsonmxmarc]

Ahh yes, Tyler, thanks for clearing that up!

Most of the time it's lack of maintenance, thrashing engine or modding engine incorrectly.

Exactly; from what i gather from your "exporters list of the goods and bads", he states that the transmission 'could use' an oil change; after 15 years of use.. 15 years without a trans oil change is a LONG LONG time on a performance vehicle, especially since oils back then weren't meant to for such rigorous abuse as they are now with more synthetic ingredients. Off the bat, that would have signalled an alarm, if the trans oil was neglected, what else was neglected? It's easy to say a car runs well at idle with low compression, as long as one of the rings isn't blown, it will idle and run properly! A compression test should have been mentioned before shipment to alleviate any legal compensation in the future..

Also, the car was not modded, it was stock.. A stock car with low compression would signal 2 things; thrashing/abuse and neglect to maintain. Thrashing is not a sufficient cause of wear and tear, however it is a necessary cause. Same goes for neglecting oil changes; its a necessary cause, but it isnt sufficient to blow a motor (could store a car for 10 years with crap oil, wont damage car per se). So basically from what i can see, the last owner didn't take much interest in maintaining this vehicle and abused it in its final legs - thus reason for sale - like most Skylines.

Just to reiterate - for future reference you can drive your car hard, and abuse it - compression will not change, however it needs to be maintained with scheduled maintenance and proper care if this is how it's going to be driven.. My compression has not changed after 30,000 km. I bought the car which showed a steady cold compression of 145 across, 155 across hot; last compression test was done last month, again 155 across - 30,000 km variance, but maintained to the T and taken very good care of.. Of course over time compression will die out, its only the natural path of any vehicles engine but i figure i can get one more summer out of it with my new build before engine work will be needed..

Have the leak down test done to insure you know the problem, again, if its the top end, do it up RIGHT the first time - read plenty and look into what others have done to make a reliable build. It cant be done cheap, but please dont cut corners, you'll be kicking yourself mid summer.

[Skym]

High oiltemps kill bearings in turbo, engine, etc. Took 35? laps to destroy bottomend bearings (impressive for stock bearings) in boosted up stock RB20DET engine without engine oilcooler in Australia. Also being turbocharged, more heat than NA engine, so oil breaks down earlier.

But being a R33 RB25DET??, should have coolant to oil engine oilcooler as stock equipment.

[Tony-R32]

Hey guys,

alot of what i've been reading in here is helpful. And before i parked my car for the winter i was finding some similar issues. I was loosing coolant at the smallest pace. When the engine was hot or running not a drop, when i let it sit for 8+ hours i would come out to a tiny pool of coolant that was dripping off the bottom point of my tranny, and the sides of the block looked a bit saturated. I was also getting some white smoke out of the exhaust...but thats kind of normal in winnipeg around this time as the temp drops.

So based on what i've read in this thread, does it look like my head gasket is the problem/ what other things might need to be replaced?

is there threads on the forum that show/ explain how to do a leak down test? Im new to nissan, and haven't really taken a deep interest in engines untill i got my skyline so im still new at this.

Thanks!