Bronze magnesium valve guides????

**gtrjon** · 08-06-2011, 10:03 PM

So i grabbed a set of supertech bronze magnesium valve guides for my rb26 along with tomei solid lifters, supertech single valve springs and retainers, and supertech valve stem seals. however today my machine shop called me and said they dont reccomend using the bronze magnesium guides because they tend to melt at high rpms and stick to the valves. ive never heard of this before and couldnt find any info on it online. i do plan on revving to roughly 9k or wherever i make power until so it is a concern. anyone shed any light on this?

**GTRADDICT** · 08-06-2011, 10:34 PM

I dont understand why people still use bronze valve guides? There we're used when gas had lead and the guides we're oil enpregnated (whatever how you spell that). Can you get like Titanium or some other alloy? Dropping a guide sucks!

**hozer** · 08-07-2011, 04:39 AM

I don't see how you could possibly melt them. Weakest link in bronze is the tin component and even that doesn't melt until 450 Celsius. The melting point for those would be farrrrrr greater than your engine would ever get (600-800 Celsius depending on the composition of the bronze).

**gtrjon** · 08-07-2011, 05:20 AM

what kinda guides are you running hozer?

**Terrh** · 08-07-2011, 10:05 AM

Melt at high RPM? Better tell BMW that. All their bike engines use bronze guides. And rev to 10k+ RPM.

I'm using the supertech guides, because I lost a motor from a cast iron guide exploding for no goddamn reason. **** stock guides.

The supertech guides are kinda shitty too though, mine took a TON of machine work to get in the head properly, and then all of them but 2 had to be reamed, and the two that didn't had have liners put in because they were oversized.

**derk** · 08-07-2011, 02:18 PM

Originally Posted by GTRADDICT

I dont understand why people still use bronze valve guides? There we're used when gas had lead and the guides we're oil enpregnated (whatever how you spell that). Can you get like Titanium or some other alloy? Dropping a guide sucks!

do you have any idea how much a set of Ti guides would cost? hahah

**gtrjon** · 08-07-2011, 02:38 PM

something like 400 bucks! i need a decision guys run the stock guides or the supertech????

**christdeyoung** · 08-07-2011, 03:43 PM

+1 one finding other guides. I put supertech in mine, and they ended up requiring a lot of machining. Apparently the hole in the tube may not be concentric enough, so the valve won't go in as straight as it was from factory.

Lifter number 8 on my intake cam was so far out (had to regrind the seat so much to compensate for the angle that the valve now sits significantly higher in the head) that
I had to use an OEM lifter (thinner than Tomei), and even a shim thinner than Nissan offers....it was like 1.55mm or something stupid. It still should work fine, it just might be a pain in the ass to set the cams up, having to find undersized shims.

I used 9.5mm shims from a Hotcams CRF450R shim kit in my motor. They don't completely fill the bucket in the retainer, but as long as the shim can't slide off the valve, and expose even a small segment of it, it's good to go (don't think you can get away with using smaller diameter shims). You can pick up a kit for less than 100 bucks that has like 3 of each shim from 1.2 to 3.5mm in .05mm increments

My engine builder said that I should have just put what he called 'sleeves' in the guides, that way the tunnel stays true to original so minimal valve seat grinding would be required, and it would be less of a pain in the ass to install the guides (head has to be oven heated several times to get the guides out, as you can't get them out fast enough before it cools). I had never looked into it further, but I dunno if I'd trust a sleeve in a shitty guide that could crack. lol

...I wouldn't risk running the stock guides though.