LarsZ28

I am installing Comp Cam 918-16 valve springs on my midly-stock L98 87 GTA.

I also bought new comp cam retainers and locks and 2 packs of different size shims.

What factory gear can I throw out? Obviously I'm replacing the retainers/locks and springs, but I've heard talk about rotators??

Also, once I have removed the factory items and discarded them, how do I know much shim height I need to replace what I have removed?

Thanks in advance...

sofakingdom

iTrader: (1)

All 16 valves have oil shields; sheet metal "sleeve" kind of things that cover the top half-inch or so of the springs. Throw them away.

Rotators are on the exhaust valves only. They're big thick heavy blobs about .100" thick. Throw them out, and replace them with shims underneath the springs.

I'm guessing you REALLY meant 981, not 918?

If so, then depending on what cam you're using, you may need to be REAL CAREFUL about how you set them up. You'll get best results if you set their installed height at 1.700". There's not alot of room for error or tolerance there.... use a valve spring mic.

http://store.summitracing.com/partde...rt=PRO%2D66902

You may find that it's easier to get it right if you use .050" offset keepers, to allow the retainers to sit higher up on the valves; and more shims under the valves. It's impossible to predict how much shim you'll "need" without measuring YOUR heads. They're all different... especially if the valve seats have wear, or have ever been ground. This is the kind of thing that makes engine BUILDING different from just REPLACING PARTS.

LarsZ28

Thankyou so much Sofa...

It's an all original L98, this is the first time the valve covers have even been removed.

So for all valves I can throw away the oil shields?

And for the exhaust only, I throw away the rotators and then use .100" worth of shims under the springs? I do not have a guage to accurately check for installed height. Is it best that I just leave the rotators on the exhaust valve springs then and just throw out the oil shields? Must I use shims under the springs if I remove the oil shields?

Is all this worth it for a stock engine that wont be raced and only street driven? Maybe best to play it safe and keep the original oil shields and exhaust rotators if there is a chance I may not get it right?

Cam is stock, as is the rest of the motors internals.

Thanks again Sofa, you've been very heplful.

sofakingdom

iTrader: (1)

Yes. They are ineffective and do nothing but act as dead weight at the valve stem. Use "positive" valve guide seals instead of those thigns and the stock O-ring seals; the kind that slip down over the guide and grip it with a wire or band around them to hold them in place. If you include the stock O-rings, don't forget that the correct order of assembly is to compress the spring, put the retainer on, put the O-ring on ABOVE the retainer but below the keepers, then the keepers, then let the tension out of the compressor. The O-ring is only supposed to keep oil from running down the valve stem from on top of the retainer. If you put it on before the retainer, it does NOTHING, and only acts as dead weight hanging on for the ride.

Get rid of the rotators. They are basically dead weight in the worst possible place to have dead weight in a valve train.

The stock L98 cam is amazingly weenie. If you plan on keeping that, you can get away with less precision in how you set up your valve train. I would still STRONLGY siggest getting a valve spring mic such as the one I posted; but you can probably "get away with" using the same thickness of shims under all the springs, plus an extra .015" to make up for the missing oil shields, plus the extra .100" under the exhausts.

five7kid

iTrader: (14)

Are you sure about the extra .100" shim for eliminating the rotators? I may be all wet, but I thought with all new springs and retainers, you'd be able to set them up for the correct installed height without that kind of shimming.

sofakingdom

iTrader: (1)

The spring pockets are usually cut deeper on the exh side.... that way, they get to use the same springs on both sides, at the factory.

five7kid

iTrader: (14)

I didn't realize that. Makes a little sense when you think like the factory.

But, I haven't messed with factory 3rd gen heads much. I also don't tend to think like the factory. . .

At any rate, checking installed height on each and every valve is the right thing to do.

sofakingdom

iTrader: (1)

Part of my "career" has been spent as a mfg engr... I tend to ALWAYS think like that. It's a disease.

five7kid

iTrader: (14)

So, it's the cost trade-off between machining spring pockets two different depths, or having to kit two different valve springs that can be inadvertently switched on the assembly floor.

sofakingdom

iTrader: (1)

Yup....

The pockets are a CNC setting, and the springs are .... well, dependent on a bunch of ..... humans .....



Which would YOU do, if you were running the company?

five7kid

iTrader: (14)

Leave off the rotators and save even more money.

Damon

The shim you will need when you replace the rotator/retainers with standard non-rotator retainers will typically be about .060" thick. PART OF the thickness of the rotator/retainer is made up for by maching the spring pockets deeper, but not all of it. Typically .060" is about right- that would be the thickest shim supplied with a typical assortment kit. They are usually .015", .030" and .060"

Pat Hall

iTrader: (31)

When I had my 083 L98 heads redone with new Isky 235D springs, my machinist used a .090" shim IIRC, under all the exhaust springs. You can visibly see that the pockets are deeper on the exhaust side when the springs are removed. I guess you don't absolutely HAVE to use a valve spring mic to set up the new springs with the stock cam, but I still would none the less. I'd rather know it's right for sure than have to wonder about it. Every set of heads I've ever had redone, no matter what machine shop I've used, the shields and rotators are always the first thing they chuck in the trash, right along with the weak factory springs.

LarsZ28

Can you use two shims in the one pocket? Or must you use only one that is the right thickness that you require?

Pat Hall

iTrader: (31)

There shouldn't be a problem using two to achieve the required thickness. Like my heads for instance. .060 and .030 are both commonly available shims, and stacked together makes .090.