bronze or stock valve guides?

[recordsj]

rebuilding my 1500 midget engine
what are people's thoughts between getting bronze or stock valve guides?
what are the benefits/trade-offs of between the two?

 

[hooey]

I allway use bronze but you must get them ream to fit your valve

 

[Scott_Hower]

Silicon bronze main benefit is that it is self lubricating.

 

[Hap Waldrop]

Silicon bronze main benefit is that it is self lubricating.

What Scott said, and contrary to popular thought, they normally last longer too. The only concern with a bronze guides is they take more clearence, especially on the exhaust valve, as you are clearencing them to operatiing temp, not room temp, so a good .003" is needed for bronze guide as for clearence, this sometime puzzles machinist not used to using them, and setting up a bronze guide too tight can lead to issues like seized valve or even bend a siezed valve so clearence is important.

 

[hooey]

you are so wright hap thats why you must get them ream to fit your valve and alot of machine shops don't like to spend the time getting them right as I found out over the years and it why I do my own valve work

 

[recordsj]

Silicon bronze main benefit is that it is self lubricating.

What Scott said, and contrary to popular thought, they normally last longer too. The only concern with a bronze guides is they take more clearence, especially on the exhaust valve, as you are clearencing them to operatiing temp, not room temp, so a good .003" is needed for bronze guide as for clearence, this sometime puzzles machinist not used to using them, and setting up a bronze guide too tight can lead to issues like seized valve or even bend a siezed valve so clearence is important.

So what is the clearence tolerance when using the bronze valve guides that the guide needs to be machined to after installing in the head? 0.003" +/- ???

 

[Hap Waldrop]

Yep, .003" should be fine, the deal is the bronze expands with heat, and since it is sitting on the guide bore hole in the head, it has no where to expand but on the ID. Here's the deal though, it often time is near impossible to find bronze reamers for the sizes we need and with anormal steel reamers they often times grab inside the guide, and as cheesy as it may sound, you often times need to use a drill bit as a reamer to get the right size, for example on a A series engine you need a 9/32" reamer and no one makes one for bronze, just steel, so I use a 9/32" drill bit for the first fitting and then a 7mm flex hone to put my finish on them. Bronze is a unique material to have to machine, it does not like cutting oils when being machined, so it has to machined dry.

 

[hooey]

one trick I use is to heat the head too 150 -180F
in your oven and use the stock size reamer and use bee's wax to lube the reamer, you can get about two guide before you have to reheat the head !!! one othere thing I do this before I resurface the head this will work on all heads
try it hap you might like it

 

[recordsj]

Yep, .003" should be fine, the deal is the bronze expands with heat, and since it is sitting on the guide bore hole in the head, it has no where to expand but on the ID. Here's the deal though, it often time is near impossible to find bronze reamers for the sizes we need and with anormal steel reamers they often times grab inside the guide, and as cheesy as it may sound, you often times need to use a drill bit as a reamer to get the right size, for example on a A series engine you need a 9/32" reamer and no one makes one for bronze, just steel, so I use a 9/32" drill bit for the first fitting and then a 7mm flex hone to put my finish on them. Bronze is a unique material to have to machine, it does not like cutting oils when being machined, so it has to machined dry.

With teh 9/32" drill bit do you just drill the guide with the drill press? What is the procedure in doing this to avoid damaging the guide?

 

[Hap Waldrop]

I don't find installing bronze guides with hand guide driver and hammer to be difficult, alot easier than installing cast iron guides actually, I've probably installed a hundred sets in my life. Now removing MGB guides well thats a different story, I first shock them with guide driver and hammer to move them just a tad from their original position then use a press with the same guide driver to remove them the rest of the way.

Ok first off the 9/32 drill is a A series engine thing, I can't remember the drill/reamer size used for 1500, but the valve stem is bigger than the A series engine. mentioned earlier you'll need a flex hone to finish them as well. It can be done with a hand drill with the head on a bench.