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Compression Ratios?

kx2fity

By kx2fity,
in Western Australia

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kx2fity Collaborator

kx2fity

Posted
Posted

Hey guys so I had my future skyline checked over today by TopRacing "Must say Awsome company, easy to deal with and willing to give you their time"!

Ok so heres the deal: The found nothing majorly wrong with car except few minor wiring problems! Ignition is fueling when switched to accessories 'instead of 2 secs stop it is continue to pump fuel' kinda dangerous but easy fix! 4th gear grinds a little bit with quick shifts! apparently an easy enough fix

The Problem 'Compression ratios' 150 145 140 140 135 125? The guys say its not that unusual and the car could last quiet a bit longer without any problems? Any opinions would be greatly appreciated as i am purchasing vehicle on satdy!

They quoted me about $4000 to completely rebuild engine (stock internals 'no forgies) does this sound right?

Is there any other ways around this?

So anyway I was able to negotiate with seller and he has knocked a further $2000 of the car! which I feel is fairlly reasonable? I love the car and it seems this is the only future prob i may be faced with!

Would greatly appreciate opinions?

Cheers,

Dan

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Steve Grand Master

Steve

Posted
Posted

the fuel pump thing isnt really a problem - its just a nissan thing, the fuel pump being shut down after it primes, probably a nvh thing is all - sounds like someone at some time has been modifying the setup.

gearbox - redline shockproof lightweight will sort out the synchros, about $33/litre, you need ~ 2 litres

The uneven compression, I would be very wary, the nissan manual states the maximum acceptable variation between cylinders is 14psi (1kg) - you have greater than that on two cylinders (admittedly #5 is close)

4k is very, very cheap for a rebuild. do make sure when they say rebuild, they mean a full rebuild, and not just a freshen up (rings, bearings, timing belt water pump etc) cos if there is any bore damage, it may end up costing alot more than 4k if that is the case. (and btw, forged pistons dont usually cost much more than OEM pistons and rings)

A much cheaper option would be to buy a 2nd hand engine from japan - can usually get a good one for under 2K, but then you are looking at labour to swap parts that may not be included with the engine, timing belt, fluids etc.

buyer beware, I wouldnt buy it, imo compression all over the place indicates a mis-used, under serviced, potential nightmare

kidd Mentor

kidd

Posted
Posted (edited)

-with 4k-5k id be getting forged man.

-sorry guys but redline gearbox oil is no good long term, esp on getrag gearbox, but keep using it if it works for you

-If your syncros r gone they will need replacing (redline just hides this fact until more damage takes place).

-castrol syntrax 75w/90 is safer overall.

Edited by kidd
Ant97GTR Grand Master

Ant97GTR

Posted
Posted

Hi Daniel,

The compression of cylinders 5 and 6 are a worry (part. Cyl 6). As stated above the nissan manual says the max variance between cyl should be around 14 psi. So if the highest reading is 150 the lowest should be a minium of around 135.

This doesn't mean that its going to blow up any minute but do keep some money spare for a rebuild in the future.

Cheers

kx2fity Collaborator

kx2fity

Posted
  • Author
Posted
Hi Daniel,

The compression of cylinders 5 and 6 are a worry (part. Cyl 6). As stated above the nissan manual says the max variance between cyl should be around 14 psi. So if the highest reading is 150 the lowest should be a minium of around 135.

This doesn't mean that its going to blow up any minute but do keep some money spare for a rebuild in the future.

Cheers

Hey Ant, I wouldnt of had this dilema if I had been able to buy your car! haha I came up with $$$$ about 2 weeks after you sold spew!

Yeh I have also taken that into consideration the $4000-$5000 and have negotiated price down $3000 and maybe even try go lower! Everything else in the car is done so if I was to spend the extra $4000-$5000 I would have a a fairlly decent car!

Ant97GTR Grand Master

Ant97GTR

Posted
Posted

Not much you can do about that mate, it obviously wasn't meant to be.

Good negotiating right there but the main thing is that you know what you are getting into....which is why its important to get these test done before a purchase. Good luck with it all. :(

rev210 Grand Master

rev210

Posted
Posted

get a leak down test done. Those last compression figures aren't flash at all. This is more so if it's an RB25det.

This motor is in need of a future rebuild for sure but, like everything it's how soon.

It's important not to lean on this engine for big power increases given it's pretty tired. The mechanics are correct in saying that the motor might last a while longer, if you don't thrash it.

4th gear is syncros, an easy fix by either buying a new gearbox or fixing that one. $1.5k Don't listen to the old 'just slap redline in it...' thats not a fix it's a mask.

The description you have given paints the picture of a bunky. If its a bunky price then you know what you are in for. If it's not mega cheap then don't fool yourself.

Put the onus of fixing those things on the owner. $2k doesn't buy a rebuild installed and tuned.

Steve Grand Master

Steve

Posted
Posted
4th gear is syncros, an easy fix by either buying a new gearbox or fixing that one. $1.5k Don't listen to the old 'just slap redline in it...' thats not a fix it's a mask.

$66 v's $1500... hmm

I have run gearboxes for years with worn synchros, just by using redline lightweight shockproof - not everyone has (or wants) to spend $1500 when for less then $100 you can solve the problem - but if it works for you...

rev210 Grand Master

rev210

Posted
Posted
$66 v's $1500... hmm

I have run gearboxes for years with worn synchros, just by using redline lightweight shockproof - not everyone has (or wants) to spend $1500 when for less then $100 you can solve the problem - but if it works for you...

Hi Steve,

I too have used redline shockproof for many years. On shagged syncro gearboxes. When the syncros are worn badly the shift quality sucks, it's still sucks after adding redline it just doesn't make crunching sounds. I find on draining the oil after the regular interval there is plenty of metal content to confirm wear is still occuring at higher than normal levels.

The problem is that when you have a car that has this many untidy issues, it's likely the syncros crunch because the gear oil wasn't changed at regular intervals, like alot of skyline owners are guilty of. That means not only are the syncros worn but probably the shift forks and everything else.

Like I said $100 doesn't solve the problem, being worn gearbox. What it does do is take away a symptom ,which is a good thing but, like a cold tablet it's only masking the problem.

kidd Mentor

kidd

Posted
Posted
Hi Steve,

When the syncros are worn badly the shift quality sucks, it's still sucks after adding redline it just doesn't make crunching sounds. I find on draining the oil after the regular interval there is plenty of metal content to confirm wear is still occuring at higher than normal levels.

technical terms, redline has high concentration of Molybdenum disulfide, which is eating the s**t out of whats left of the syncros man. call it hyperlube like graphite

I reckon mixing lightweight and heavyweight Rline at a certain dosage will be the best/worst experiment, what u think rev? Steve try it!!!!! :)

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