PDA

View Full Version : Sr head flaws?



Miami240
02-10-2003, 03:13 AM
I've read somewhere a few times something about Sr's heads not being designed properly for high revving. This was brought up when comparing the KA and the SR. Someone mentioned something about the Sr valvetrain breaking a lot during high revs while the Ka bottom end was it's flaw to high revving. Can anyone clarrify this?

**DONOTDELETE**
02-10-2003, 03:18 AM
The SR has only one cam lobe for each cylinder and a hydraulic lifter and rocker arm. If you rev the crap out of it there is a possibility that the rocker will start to bounce and smack a valve. What people don't tell you after they've said that the SR valvetrain is terrible is that it will rev to 7500 all day every day.

SRFiveTen
02-10-2003, 03:32 AM
y-shaped rocker arms pivotted on hydraulic lifters is the flaw in valvetrain design of the sr.

if you over-rev an sr, a rocker or two is likely to fall off, causes the valves to stay shut, or causes the shims to fly out and do some damage elsewhere.
[if the rocker gets jammed, then valve(s) might get stuck open,,,, and because nissan engineers aren't as considerate as toyota/yamaha camp, valves kiss pistons]

over-rev is considered beyond 7500, perhaps close to 8000 in stock valvetrain.

one of the most common occurance of over-revving is a driver error, while he shifts from 1 to 2 to 3 and then back to 2 instead of 4.

rocker arms have been known to fall off even from a shock such as sudden encounter of a mountain side by the front fender; or simple spin outs resulting in reversing while in forward gear.

rocker arm stoppers are supposed to help.
however apex-i does advertize camshafts that will spin stock sr to 8500rpm without head modification, without rocker arm stoppers, just with their double valve springs.


ka is a long stroke motor.
long stroke motor doesn't like to turn high rpm. it is much happier pounding out thick torque at lower rpm.
i don't think ka has flaws in its design.
i believe there is a flaw in the builder's mind if he wants to create a ka that revs as high as built sr.

NOSTALGIC_HERO
02-10-2003, 09:09 AM
well put. that is quite a scary thought of rockers flying out from "emergency maneuvers"

Hugh
02-10-2003, 11:04 AM
The rocker stopper is a great mod for the average guy. It's cheap (under $100) and will save you when you do something stupid. (Me, do something stupid? No... http://forums.freshalloy.com/ubbthreads/images/icons/smirk.gif ) If I had one in my first engine, I'd still have my first engine.

The rest of the problem can be solved by going all into solid lash. (With a Lash Killer Kit) When you remove the hydraulic lash adjusting capabilities of the SR, its head will rev for days... but the block is supposed to give out above 8000 RPM. I take my SR to 8000 sometimes, with only a headgasket and a rocker stopper kit. It keeps taking the beating... but my last head didn't even make it to 8000 when it died.

**DONOTDELETE**
02-10-2003, 12:14 PM
I've had mine to 7750rpm on several occasions with no problems. Maybe I'm just lucky... http://forums.freshalloy.com/ubbthreads/images/icons/crazy.gif I'm planning on installing some valve springs and RAS in the near future.

Cicero
02-10-2003, 12:36 PM
I've taken mine pass 8000rpm, according to the tack. That how i found out my motor came w/ a reprogrammed ecu.

KSU_S13Less
02-10-2003, 01:48 PM
Hopefully my motor I'm building will be able to handle the extra revs. Any suggestions on which lash killer kit to use? Also, has anyone thought about switching to the newer style roller cams and roller rockers? I know that the stock cams aren't as agressive but won't it reduce some of the friction in the valve train?


Regards


Gregory

s14turbo
02-10-2003, 01:59 PM
there's nothing you can do to totally aleviate the rocker arms fyling off on the sr. combine this w/ the fact that the sr tranny is pretty weak, and you've got a recipe for failure. everytime you misshift or blow your tranny the rocker arms fly off. it's a problem w/ all rocker arm motors in general not just sr's.

KSU_S13Less
02-10-2003, 02:05 PM
Well, the tranny part isn't too bad as all we have to do is get a usdm tranny and swap the bell housing. It's been my impression that rocker arm stoppers help significantly reduce the chance for failure. I'm not talking about reving my motor into oblivion. I plan to keep the revs around the low to mid 8000ish make--as long as I'm still making decent power. http://forums.freshalloy.com/ubbthreads/images/icons/wink.gif Otherwise I couldn't justify the extra wear and tear. http://forums.freshalloy.com/ubbthreads/images/icons/grin.gif

Regards


Gregory

iHATEstupidity
02-10-2003, 03:28 PM
</font><blockquote><font class="small[/img]In reply to:</font><hr />
it's a problem w/ all rocker arm motors in general not just sr's.

[/QUOTE]

quite incorrect. the sr20 just has this particular problem because its rocker arms are not solid-mounted in any way. thus, it has a floating rocker setup. not all rocker arm motors have floating rockers. best example? domestic V8s.

THINK

KSU_S13Less
02-10-2003, 04:23 PM
</font><blockquote><font class="small[/img]In reply to:</font><hr />
quite incorrect. the sr20 just has this particular problem because its rocker arms are not solid-mounted in any way. thus, it has a floating rocker setup. not all rocker arm motors have floating rockers. best example? domestic V8s.

[/QUOTE]

I'm not exactly clear on this. Is it the fact that stock the lifters are hydraulic and not solid?

Regads


Gregory

asad
02-10-2003, 04:49 PM
</font><blockquote><font class="small[/img]In reply to:</font><hr />
I'm not exactly clear on this. Is it the fact that stock the lifters are hydraulic and not solid?

[/QUOTE]

No, it has nothing to do with the lifters. It's because the rocker arms just sit on their pivot, but aren't actually attached (like with bolts or screws) in any way. This means they can fly off if the motor overrevs.

Asad

SRFiveTen
02-10-2003, 05:56 PM
</font><blockquote><font class="small[/img]In reply to:</font><hr />
well put.

[/QUOTE]
your compliments make me http://forums.freshalloy.com/ubbthreads/images/icons/blush.gif not!
i just hope you don't include me in the "all" that you hate http://forums.freshalloy.com/ubbthreads/images/icons/grin.gif

while we're on the topic of rocker arms, next time one has the cam cover off, i highly recommend inspection of the rocker arms, there are only eight.
view them from each side of the engine bay.
if you see any blackened rocker arms, you need to take them out and clean out the oil squirting hole.
if beyond cleansing, replace them with rocker arms for fwd sr.
rocker arms shouldn't be black with caked oil, unnatural to say the least.
lack of lubrication in this area will cause premature wear on cam lobes or rockers; excess heating of rocker arms which may lead to rocker breakage.

if the shims were taken out of the valve spring retainers, make sure you put them back correctly!


sr20 have been dubbed as to have "heart made of glass", which would shatter when over-worked.

iHATEstupidity
02-10-2003, 05:59 PM
and i call the sr20 the engine with the block designed by nissan's top engineer, but with the head designed by the summer intern.

THINK

Kookz
02-10-2003, 06:01 PM
</font><blockquote><font class="small[/img]In reply to:</font><hr />
but with the head designed by the summer intern.

[/QUOTE] Too busy with another kind of head, perhaps?

V8Styles
02-10-2003, 06:28 PM
can anyone add more information on how to clean rocker arms ?

KSU_S13Less
02-10-2003, 06:58 PM
</font><blockquote><font class="small[/img]In reply to:</font><hr />

No, it has nothing to do with the lifters. It's because the rocker arms just sit on their pivot, but aren't actually attached (like with bolts or screws) in any way. This means they can fly off if the motor overrevs.

[/QUOTE]

Coolbeans. Has anyone heard of swapping to roller rockers and roller cams? The reason I ask is when I tore down my motor I noticed that the rocker arms had excessive wear (looks like from lack of oil). Am I out in left field?

http://forums.freshalloy.com/ubbthreads/images/icons/grin.gif

SR510,

The SR head was designed by the summer intern, who ended up getting hired by GM. *lol*


http://forums.freshalloy.com/ubbthreads/images/icons/grin.gif Regards


Gregory

**DONOTDELETE**
02-10-2003, 07:08 PM
</font><blockquote><font class="small[/img]In reply to:</font><hr />
combine this w/ the fact that the sr tranny is pretty weak

[/QUOTE] ?!?!?

Who says the SR trannie is weak? I've never had any problems with mine... and I've never known anyone else to have problems with theirs... http://forums.freshalloy.com/ubbthreads/images/icons/confused.gif

NOSTALGIC_HERO
02-10-2003, 07:13 PM
HAHAHAH!! its weak? then if thats weak, which is strong??

this is knowledge typical of 1 month SR fever. you are at that critical point where you can be saved.. IV some Freshalloy and you will be a healty person in a few weeks.

SRFiveTen
02-10-2003, 10:49 PM
valvetrain design of sr is fit for street use.

however, once the safety features built-in by the engieers are removed by wannabe racers, the fragile heart becomes vulnerable.
for example, rev limiter. guess who programmed that? and for what reason?

even if the rev limiter was to be removed, power curve doesn't skyrocket beyond 7000rpm.
stock turbo charger doesn't pull that hard beyond such rpm.

i believe sr valvetrain is innovative, on the street level, for which it was designed.
four cam lobes serving 8 valves via four y-shaped rocker arms pivotted on hydraulic maintenance free lifters.
light weight camshaft with minimal friction, ideal for maximizing performance within a given boundary.
reduced component count minimizes the risk of parts failure and lowers cost of production.

designers were given certain criterias to meet with their finished product.
racers may not have been pleased with the design, but when engineering production engines on a limited budget, race division probably had little or no say in the matter.

sr rocker arms do not hinder power production untill you modify the engine and shift the power band beyond factory rev limit.

Hugh
02-11-2003, 12:56 AM
</font><blockquote><font class="small[/img]In reply to:</font><hr />
Any suggestions on which lash killer kit to use? Also, has anyone thought about switching to the newer style roller cams and roller rockers?

[/QUOTE]

Lash killer kit - Tomei.

Roller Rockers on an SR20DET?? WTF are you talking about?



</font><blockquote><font class="small[/img]In reply to:</font><hr />
there's nothing you can do to totally aleviate the rocker arms fyling off on the sr. combine this w/ the fact that the sr tranny is pretty weak, and you've got a recipe for failure. everytime you misshift or blow your tranny the rocker arms fly off. it's a problem w/ all rocker arm motors in general not just sr's.


[/QUOTE]

Gee... they don't fly off whenever you blow the tranny... they don't just fly off, either. You make it sound like they are stuck on with friggin zip ties or something. I blew my tranny without over-revving and gee... my rocker arms stayed on. I also know a few people who take SR's over 9000 with lash killer kits installed.

I'm not saying the SR head is strong, by any means, but its not just a hunk of sh#t the way you describe it. The solid lash kit will solve the problem.

</font><blockquote><font class="small[/img]In reply to:</font><hr />
Who says the SR trannie is weak?

[/QUOTE]

If you've never blown an SR tranny yet, yours must be stock. http://forums.freshalloy.com/ubbthreads/images/icons/grin.gif

iHATEstupidity
02-11-2003, 12:57 AM
if an engine is designed to be ultimately used in a performance application of any sort, then a "successful" design is one that would not require too much modification beyond oem to be suitable for use in a high-performance application. such an engine would be testament to its over-engineered pedigree. so if an engine was NEVER intended for performance use from the factory (let's use the geo metro's 3-cyl engine, for example), then anyone who is trying to modify the motor and encounters shortcomings in its design would have no merit to any criticisms they may have of the engine's construction. but if an engine was obviously built for a performance vehicle-and it was obvious that the engine would be adopted by aftermarket tuners, and would also be used in various racing bodies and campaigned by the factory-then it is only natural for people to grouse about the parts that they discover to be a common Achilles' heel in the design.
a lot of toyota's "street" motors are quite, well-overbuilt. a lot of credit for that can be given to yamaha's guidance imo.

THINK

SRFiveTen
02-11-2003, 01:25 AM
</font><blockquote><font class="small[/img]In reply to:</font><hr />
it is only natural for people to grouse about the parts that they discover to be a common Achilles' heel in the design.

[/QUOTE]
people who can't shift should grouse about their coordination before pointing fingers at the engineers.

weak, under-engineered or designed by a drop-out, sr is capable of producing plenty of power, on or off the street.
i am sure many of you have dreamed of custom cylinderhead built by toda. how many do you think are being driven on the tracks, yet alone the streets?

plenty of aftermarket tuners have tweaked with sr.
most punked down and lived with the valvetrain.
many can point out the weakness. most don't have the ability to improve it but b!tch.
fact remains that well-prepped sr can spin &gt;11000rpm.
how many times do you peg your rev limiter in a day?

as for campaigning race teams, nissan was too broke.


wake up and realize that the common Achilles' heel is operator error!

iHATEstupidity
02-11-2003, 02:08 AM
yah or wake up and realize that i am a fan of the sr20 but am also able to admit that there are certain parts of its design that aren't the greatest. you can't honestly say that you haven't at times wondered why they didn't use a better valvetrain design on all sr20s (gti-r aside) from the factory? of course, it is all a moot point since nissan did what it did, and all the complaining in the world isn't going to change that, but people are just light-heartedly pointing out what is, indisputedly, a particular element that could have seen some improvement from the factory, had the factory wanted to improve on it.

THINK
EDIT: and yup, most valvetrain failures are a result of user error/stupidity...and unfortunately, a lot of those users go on to blame the motor for their mistakes.