I am about to replace the valve seals on my L98 91 z28. I figured that I would replace the old valve springs, pushrods, and rockers in the process, and I just have a couple of questions. I was going to order the 1.6 ratio comp pro magnum roller rockers to get alittle more lift out of the stock cam.

I went to summit racing and they have part number 1318-16 as being non-self aligning although they are listed as self aligning other places. Is this the part number for the self aligning ones or not?

I have also heard that using a 1.6 ratio rocker causes pushrod clearance problems on the stock heads, what experiences have you had with this? I have seen that most of these issues seem to occur on earlier L98 heads, but I just want to make sure.

I am also going to use the stock valve covers and have read about the modifications that have to be made, but I just want to be sure about this. I planned on following the instructions shown on this page http://www.hotss.com/Members/scott_vaca/pro-mag.htm and just wanted to make sure this was adequate or should I actually grind the supports.

Lastly, I was also going to replace the stock pushrods with some comp high energy ones and was wondering what length are the stock ones. 7.195" is what I think is the stock replacement but I am not sure.

Thanks in advance for your guys help. I just want to make sure everything will go smoothly before I place the order

 

Bending or grinding the supports nets the same result, bending is easier. I just didn't think of it when I modded mine with a grinder.

 

There is a fellow on here who's name escapes me right now, that has done the 1.6 rocker swap on an otherwise stock L-98 and he claims it is a worthy swap. As far as pushrod clearance, sometimes it can be an issue, comp cams makes a tool to elongate the hole for clearance but I would prefer to take the heads off to do this. That is really a crap shoot, just have to check the clearance and see what you come up with.
As far as valve cover clearance, I can tell you what I have done in the past that works super and requires no bending or grinding, just double up on the valve cover gaskets. It's simple, it works.
My 454 chevelle runs the stock valve covers, very very short, and by glueing 2 gaskets together I can run Crower chrome molly full roller rockers under there, and people think it's stock, very sneaky.
I also do the same thing on my 70 Firebird, I run Harland Sharp full rollers on it with stock covers, just double up the gaskets, since it is only the poly lock that gives you interference problems anyway.
If I ever put the 1.6 rockers on the Iroc, or 1.5 full rollers for that matter, I will probably just double up the gaskets to gain poly lock clearance. Just an option, hope that helps, Larry.

 

I've done the same with cork ones, but I don't think this would work with the factory rubber gaskets. Anyone know if it's possible to put a cork gasket on the stock valve covers.

 

Sure why not? All the parts stores around here sell the cork gaskets, I even have a fel-pro part number for the extra thick cork gasket for stock valve covers. Glue a pair of them together and you will have more than enough clearance. Larry.

 

Poly locks aren't the issue with the pro-magnums. The trunnion is too wide to fit the valve cover center support between two installed rockers.

In any case, any time *I've* had poly-lock/valve cover issues, I just ground the wrench flats down (so the locks re shorter, not narrower of course)...they require no torque, so you'll never use the strength the "tall" flats provide, plus, in both of my applications, the set screw is so far down in the poly lock the additional thread area (which is where the cover hits) is worthless. If poly-locks weren't so generic, they could be made shorter by the manufacturer. Only difference between that and doing it yourself is looks, it doesn't affect strength.

 

Well shucks low-tec, I ran out to the garage to get the number for ya and I have already cleaned up my mess and threw the packaging away,,,,but anyway a good counter person can look it up, Fel-Pro makes the cork gaskets for our cars, I just installed a pair of the extra thick ones on my Iroc. Larry.

 

Fel-Pro Corklam valve cover gaskets (summit part # FPP-1648) for our cars are 0.25 inches thick while the other brands are 0.172 inches. I am not sure if these are the ones you are talking about firebirdjones? By the way thanks for the advice on the rockers. I think I am going to order them, but I am worried that I could run run into the pushrod interference problem. I wanted a little extra lift out of the stock cam without having to pull the heads, so having to machine the heads would just kind of defeat the purpose. If I was going to pull the heads I would just do a cam swap, if you no what I mean.

 

I am with ya on that one Naz, with that much work involved why not just stick a new cam in, I agree 100%.. I was thinking of doing the 1.6 ratio swap myself since I have to do valve seals sometime in the future, but if there are interference problems with the pushrods I won't bother. I have a set of 1.6 ratio rockers on a 327 in another car with a set of old camel hump heads and there was no issue with that. But then again, you never know, and I hate to plunk down $300 + for rockers and find the pushrods need more room.
The tool they make for that is a do-it-yourself kind of tool, it is made to fit over the hole and then use a 3/8 drill bit to elongate the hole, very simple, but removing the heads would be best due to metal shavings. Although if you are carefull and you have the intake off, you could try catching them underneath with rags, shop vac, what ever,,,,but I don't like chancing it. Besides, like you said, even at that point, if you already have the intake off, why not pull the water pump and timing cover and just stick a cam in there.
I mentioned before about a fellow on here with an L-98 Firebird that did this swap, I think he said he had no interference problems and the swap was worth while. I can't remember his user name but it's a white firebird, that shows up in his sig, I believe the car was running in the 13's with minimal bolt ons, hopefully he will see this post and chime in here.
As far as the gasket is concerned I believe those are the gaskets you mentioned. Should be able to find them locally, there are several stores near me that carry fel-pro stuff. Keep me posted if you find out anymore on the rockers and I will try to find that guy I am talking about and shoot him an e-mail too, Larry.

 

I will let you know if there are any problems with the swap. I did alot of searching on here about swapping to 1.6 roller rockers and it seemed like quite a few people had no problems, but others did. I noticed that most of the people having the problems were 85-89 LB9 and L98s. It seemed like most of the 90-92 owners reported no problems. Is there any difference in the earlier and later madel L98 heads? I no they made the transition to self aligning rockers in 88-89, and was wondering if the pushrod slots changed as well.

Thanks for all the help,

Terry

 

Terry, if they did make the change to self aligning rockers sometime along the line, then yes the pushrod slots usually change. I will try to describe it best I can.
Without the self aligning rockers, the push rod slot is an oblong hole that is very close to the width of the pushrod to help align the rockers. If they are self aligning rockers then usually the push rod hole will be perfectly round and rather large since the rocker is now guided by the groove at the valve stem tip. The large perfectly round hole is common in aftermarket heads so clearance is not an issue, then guide plates are also usually installed so any rocker can be used. I was not aware that GM made a change to self aligning rockers during the production run of the 3rd gens. That could play a role in whether or not the 1.6 ratio is a direct drop in mod or not. I never gave it much thought when i was changing my valve cover gaskets, never looked at the push rod hole. This makes me want to take a valve cover back off and have a look...mine is an 88 iroc L-98 car, so it would be interesting to see and find out when this change over accured.
Can you or anyone shed some light on the self aligning rocker change over? thanks, Larry.

 

As far as I know it happened in 88. Since the transition was happening there are some 88s that have both self aligning rockers and the oblong pushrod hole like you discribed. I think after 88 all of the thirdgens had self aligning rockers but I am not sure about the pushrod hole. If any of this is incorrect someone please chime in.

 

Thanks Terry, I will pull one my covers off and check it out, you now have me curious. Thanks again, Larry.