View Full Version : How do shims on the SR come off while driving?

05-21-2009, 05:24 PM
Just had my engine tuned today, maxed the GT3076 and everything seemed fine. After about 100km of driving, i made a turn and had some wheelspin after. Suddenly i heard a loud bang, almost like from the exhaust, and the SR was running on three cylinders. There also was a loud licking noise from the head, so i immediately turned the engine off. Pulled the valve cover and discovered that one shim had come out of its retainer and was now laying loose in the head. Engine RPM was about 5-6000rpm with quite little boost due to the wheelspin. Had checked the camshaft clearances before I went to the dyno, and it was 0,15mm on that shim, which should be just fine (nissan reccomends between 0,14 and 0,17mm) It happened on the shim (not guide) on cylinder 1 on the exhaust side.

Head spec:
Supertech 110lbs dual springs
Tomei solid lash adjusters
HKS Step 3 cams 264in 272ex 11.5mm lift
HKS adjustable cam sprockets
New rocker arms
Shimmed all valves to 0,14-0,15mm



How can this have happened?
I don't want to put it back there, just to have the same happen again later. Thanks in advance :)

05-23-2009, 01:28 AM
would think it may be something to with the rocker arm floating at high revs think it is called floating am from iceland so the english is not that good
dont know if rocker arm stoppers will do any good but they are suppose to minimize the floating and less chance of this happening og even the rocker braking

05-23-2009, 02:46 AM
I read that since I have solid lash adjusters, there would be no need for rocker arm stoppers. And if the arm floated, why didn't the guide shim, or shims on any of the other valves, jump of?
I think it is a bit unlikely that the arm floated, given the fact that i only had 5-6000rpm when it happened, while the springs are rated to be safe upto 10 000rpm with the current cams.

I had a cylinder leakage test done yesterday, all of the cylinders have the excact same low leakage as before. But this test has been proven wrong before -an MR2 had 2 bent valves, but the leakage was just fine.

So now I have narrowed it down to four possible reasons:

* Retainer machining fault - check dimensions
* Spring fault - check for breakage and possibly remove to check for pressure
* Something went through the engine and got caught between the valve and the valve seat, causing the valve to remain open. This should have left marks on the piston aswell as on the head, and possibly caused the valve to bend. Found nothing on yesterdays cylinder leakage test, and the plug also looked fine. Will have to borrow a mini-cam and lower it into the bore some day! This object must also have passed on and went through the turbocharger, the turbine fan should have been visibly damaged by it, will check this later on.
* Valve got stuck in valve guide - remove head, check for valve guide play, possibly replace guides. The most time consuming option, but if i cannot find anouther fault, I'll have to do it. Don't want the same to happen again, possibly on VOT at 8500rpm..

A few pictures of the parts involved.

Rocker arm

Guide side

Shim side (bit fuzzy picture, but no visible damage)

Shim with quite deep scraping marks (nearly invisible in picture)


05-23-2009, 05:51 PM
i know its not a normal thing to do, but its a semi-fix.

instead of using one flat shim per rocker arm, use two grooved shims. The rocker arms will have to be modified on the one sid to fit inside the groove of the shim. I know a D1 guy who did this with his SR for a long time and it eliminated valvetrain issues, if your only revving ot 7500 at least.

this is my suggestion t least, others will have their own.

05-24-2009, 03:55 AM
Did you grind away the rocker at all when installing the Tomei solid setup.

I can't speak from experience but I recall reading somewhere (possibly Zilvia and suppsed based on the Tomei instructions) where the rocker needs to be slightly ground away so it doesn't foul/catch on the retainer.

05-24-2009, 04:02 AM
This is the rocker arm clearancing I was talking about - refer to page 2.


Full article


05-24-2009, 06:12 AM
Thanks for the input. No i have not ground away the edge of the rocker arms as i have HKS cams and measured the clearance between tip of rocker arm and shim to be 0,2mm on fully opened valves. But for security, I'll do it now. :)

As far as a solution goes, I think my valve guides are worn out. Engine makes a bit of blue smoke when the throttle is released on high rpm, and clear fuel is blown into the catch tank on full boost. Piston rings are fine, so I'm prettymuch left with valve guides as the only option. Had the valve guides checked by a local engine mechanic, and he claimed they were fine, so I didn't take much notice of them afterwards, although they have run in excess of 100 000 miles..

05-24-2009, 07:17 AM
Exhaust valve guides wear out quicker than intakes due to heat - mine had excessive wear and were replaced after just 40,000 klm's although I track my car as well.

05-24-2009, 08:00 AM
Yeah, i seem to hear that alot these days, its crucial to replace exhaust guides.. Mine hasn't been driven on too many tracks, but the previous owners (who have driven the 170 000km) have abused her quite a bit.

The big question still remains if i should lower the rev and boost limit and drive her this season, or if i should pull the engine apart and have the valve guides changed -making this the third season without driving..

05-25-2009, 08:13 PM
The same thing happened to me about a month back. I was kinda hanging out at about 7500 rpm :auto: and I started to hear a loud ass ticking :eek: so I backed off the throttle and limped home. I had just put on a new exhaust manifold so I shutdown and made sure that all the nuts were tight. Started the car back up and same ticking. I finally pulled the valve cover and noticed the #4 exhaust shim was missing.:eek: Then there was generally alot of bad language as I was trying to find said shim.:rolleyes: I ended up fishing it out of the rear of the engine where the oil goes down with a telescopic magnet.:cool: I still have no idea why this happened but I have been up to 7500rpm :auto: since then with no problems.... FYI I have bc stage 2 cams(264/264 dur, 12.06mm lift), bc valve springs, and bc titanium retainers.

Martin XAT
05-28-2009, 10:30 PM
did you check your throttle body plate retainer screws ? those are notorious for flying off.


06-01-2009, 08:56 PM
Happened again yesterday? Shim was not all the way out of the retainer though. Popped it back in and turned the rev limiter down to 7000-7200 ish rpm.

06-05-2009, 04:43 PM
Happened again yesterday? Shim was not all the way out of the retainer though. Popped it back in and turned the rev limiter down to 7000-7200 ish rpm.

you checked the clearances before just "popping" it back in, right?

06-07-2009, 12:53 PM
Nope, didn't check the clearances. Is that in the fsm? I still have hydraulic lifters so I didn't think I had to do that, Although it maybe a good idea.