The Stovebolt Site Forums The Shop Area Engine Shop THOMAS ADJUSTABLE MAGNESIUM ROCKER ARMS FOR 235?

Hi all. I just picked up an NOS set of Thomas Hi-lift magnesium adjustable rocker arms for a 235 chevy. I'm just curious if anyone has used these or know anything about them. I plan on using them in my 261 i'm going to build and am wondering if they are any good. Thanks for any info.

Chad

Look close you sure they aren't 216 or GMC?

No, the box reads:

Thomas Magnesium Rocker Arms
Chevrolet 235 ENG
#1008 HIGH-LIFT
NEW-with replaceable tips

Do you know anything about them?

Chad

Hi Chad- Should only be 6 of them, right? 3 rights and 3 lefts? They go on the intakes and increase the valve lift on a stock cam because the ratio is 1.5:1 instead of 1.4:1. (if I remember right) Thomas, Barker, B&B and Fenton all made these in the '50's. One problem I've noticed with old magnesium when redrilling old Halibrand wheels is that it gets real dry and brittle when it's old. You may have a higher chance of breakage, especially if used with stiffer valve springs?

What Barry said!

Recently read a post on another site that said aluninum and etc rockers were only good for about 20k miles, and should be replaced in drag racing engines every 2 years. Something to do with the stress and the amount of stress. Kida like the the stuff that the airlines had to figure out a while back. If I was going to go afer them I would go for a steel rocker, with a roller, and clearanced for the lift of cam you want.
Dennis

Magnesium is a very brittle metal. In the 50's it was the wonder-metal of the time. Was outlawed in the 60's for use in lawnmower decks, too many people got hurt when rocks went through the housings, killing/maiming people. Personally, I wouldn't use them.

Aluminum rockers won't have the strength or hardness of a steel rocker. Add a little over 50% more material to get the strength of steel, but you can't come close to the hardness needed for the pounding on the valve stems. Okay to run, but definitely not a long-life product.

Phat may have a better take on aluminum rockers, but a lot of guys use aluminum roller rockers for years with no problems .Might be more of a gimmick than a necessity on a street engine but the reduced friction is worth some free power. I'm taking Chevy v-8 here, to replace the stamped steel pivot ball rockers.Old magnesium stuff is a whole different story

Tony, it's not less friction, but less mass to be moved, that much more power to the wheels. Do they make a difference? Not enough to be noticed in a street machine. If you're talking about shaving hundreths on the quarter, yes, but not much unless you have a well-balanced engine.

This is what Crane cams claims ;Gold Race (Extruded Body)
Made from heat treated, extruded aluminum billet bar stock for ultimate strength. Needle bearing fulcrum and roller tip for maximum friction reduction. Improves response, increases HP and RPM, lowers oil temp. For most 4, 6 and 8 cylinder domestic engines. Different ratios, pushrod seat offsets and stud sizes available.

Roller rockers just plain work.Less friction ,lighter weight(exp alumin) and no they dont have to be changed in a street engine.I have many sets out there with over 100,000 miles on them.(one set is in my snow plow truck now for over 10 years,racin rejects)BUT those mag racker are rare and a great coffee table item,dont use em .Nothing wrong with the stock steel not many fail ,just wear out(even then they are fixable).leave em inn the box neat item to talk about,but of no use in your 150 hp 235.really cool find!!!!

Okay Tony. I missed the roller part. Been so long since I looked at a set of them I forgot. Too damm old, I guess. The aluminum body means less mass to move, the roller bearings will do a lot for friction. But they're still not going to last as long as steel.

Hi guys, thanks for the responses. They are oxidized from sitting so long and I didn't think they'd last long because there just doesn't seem to be that much material there! I was surprised at how light they are! Much lighter compared to the stock steel rockers. Maybe i should just be on the lookout for the fenton, B&B, or Barker high lift varieties, since they are steel. Maybe your right Phat, I'll just use 'em as a conversation piece. They still got the instruction sheet with 'em so maybe i'll throw them in the display case. Thanks for all the responses.

chad

Hey Chad, let me know if you want to trade for another brand, I'm sure I could dig up a set out of my collection. Personally I would use whatever cam you want and not try to wake up a stock cam with high-lift rockers.

Hi Barry. The 261 I'm going to build is going to be kinda hot so I'm not going to be using a stock cam. I think i'll hang on to this set and search for one of the other varieties. I've seen a set of fentons before but passed up on the deal. I'll keep my eyes peeled. Thanks for all the info everyone.
Chad