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Valve guide bushings for aluminum Briggs Engines


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  #1  
Old 10-07-2008, 08:42:03 PM
Beanscoot Beanscoot is offline
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Default Valve guide bushings for aluminum Briggs Engines

In the past when I installed valve guide bushings in "modern" B&S flathead engines I would just turn a piece of likely bearing bronze or brass to fit the full length of aluminum that the valve rides in.
However, the store bought Briggs replacements are quite short, only about half as long as they "should" be to completely line the old bore.

Is there any special reason that a shorter bushing be used rather than a full length one? I see some of the Kart Racing shops sell full length guides, but maybe Briggs had good reason to make them short. All I could see is that they're quite thin so would get crushed if they were full length. Of course when I made them I would just make them thicker.

I can now borrow the installation set from a friend, so am tempted to just put in the short stock ones, but will continue to make full length ones if there's any advantage.
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Old 10-07-2008, 11:07:23 PM
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Default Re: Valve guide bushings for aluminum Briggs Engines

I never cared for the short sintered iron ones in the exhaust ports,they were really hard on exhaust valves.I usually installed brass guides inside the sintered iron guides.I think B&S did it to save a little money but I really don't think the guides need to be longer than stock,most of the wear comes at the top of guide.That said,I did put 2 guides in engines for a while,one on top of the other,just in the exhaust side but I really didn't see any gains,so I went back to just using the stock length guides.
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Old 10-07-2008, 11:27:09 PM
makoman1860 makoman1860 is offline
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Default Re: Valve guide bushings for aluminum Briggs Engines

There are 2 different length guides available, the longer one is 1.25" long. www.goodson.com has them along with the tooling.
-Aaron
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Old 10-08-2008, 02:22:24 AM
Beanscoot Beanscoot is offline
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Default Re: Valve guide bushings for aluminum Briggs Engines

Thanks for the advice. I was wondering why Briggs shows different part numbers for the intake vs. exhaust, I suppose the intake is bronze, the exhaust sintered iron?
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Old 10-08-2008, 07:07:59 AM
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Default Re: Valve guide bushings for aluminum Briggs Engines

The 2 part numbers should both be brass,the sintered iron guide is used in new blocks and I don't think it's considered replacable,if I remember correctly the repair for the iron guide was to install a brass one inside the iron one.You'll know the iron one when you see it.it's about 1/8in thick and gray in color.I believe every exhaust valve that I ever removed from an engine that used them had severe wear where the valve rides in the guide.
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Old 10-08-2008, 09:07:12 AM
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Default Re: Valve guide bushings for aluminum Briggs Engines

You can buy the larger diameter bronze guide to replace the iron part. Briggs used to use a bi-metal valve that had a mild steel stem. This worked out fine with the iron guide, but when cost reductions made the valve 1 piece, they ended up with a stainless stem. Stainless on iron is a bad deal. Goodson has the bronze guides in .283" , .310" and .376" OD's to cover all the briggs factory guides.
-Aaron
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Old 10-08-2008, 09:16:18 AM
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Default Re: Valve guide bushings for aluminum Briggs Engines

Your right,I do remember seeing replacement bronze guides for the iron ones.
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Old 10-08-2008, 11:30:14 AM
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Default Re: Valve guide bushings for aluminum Briggs Engines

I know the kart guys use full length bronze ones for durability and accuracy. I heard at race speeds the valve has to open and close 60 times a second. More accurate guides would probably cause less wear on the seat I would think, and cause less wear on the valve, expecially when the valve guide lubricant is applied. I've also heard of kart racers just stacking two stock briggs ontop of each other, but I belive that the solid one peice would be better.

Briggs made the guides/ fit from the factory sloppy, to help keep them from "sticking" open if they got any rust on them or sat for a long time, and then somebody went to turn it over. Thats what I've heard at least
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Old 10-08-2008, 11:37:10 AM
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Default Re: Valve guide bushings for aluminum Briggs Engines

if its not too much trouble, I could continue making the guides as you already are. I get ALOT of engines in that have good compression, but smoke because of the valve guides are so worn. Sometimes they wont even idle down very well just because of the oil contaminating the fuel/air mixture.
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Old 10-08-2008, 11:48:35 AM
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Default Re: Valve guide bushings for aluminum Briggs Engines

As I recall briggs ran about .003" clearance on the exhaust stem, and about .0025" on the Intake. It may seem loose, but its really not in contrast to what aircraft engines use. The karting guys run tighter, but keep in mind they run methanol and have lower EGT's and overall cylinder temperature. Bronze can make an excellent valve guide material, or a horrible one depending on what alloy you use. Stick to Ampco 45 , C90500, or a leaded tin bronze with 8-10% tin. Bearing bronze (SAE660) wears quickly, "phosphor" bronze (less than 8% tin) does as well. High Zinc (about 30%) bronze can work as well, but have troubles at extremely high temperatures.
-Aaron
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Old 10-08-2008, 11:56:59 AM
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Default Re: Valve guide bushings for aluminum Briggs Engines

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Originally Posted by CaseyJoeS. View Post
I know the kart guys use full length bronze ones for durability and accuracy. I heard at race speeds the valve has to open and close 60 times a second. More accurate guides would probably cause less wear on the seat I would think, and cause less wear on the valve, expecially when the valve guide lubricant is applied. I've also heard of kart racers just stacking two stock briggs ontop of each other, but I belive that the solid one peice would be better.

Briggs made the guides/ fit from the factory sloppy, to help keep them from "sticking" open if they got any rust on them or sat for a long time, and then somebody went to turn it over. Thats what I've heard at least
Actually,the B&S engines are built with the guides sloppy so that the valve rocks into the seat,just a little,to help keep carbon from building up on it.That's not a problem in racing engines,so you do want the valve to seat squarely but as I said earlier,I never saw any gains by stacking the valve guides.
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Old 10-08-2008, 07:46:30 PM
Beanscoot Beanscoot is offline
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Default Re: Valve guide bushings for aluminum Briggs Engines

Well I think in the past I used 660 bronze or phosphor bronze!, or even plain old brass if it was all that was handy. Anything's got to be better than cast aluminum, right?

Well I suppose I'll order a few long guides from the Kart shops or Goodson, and assume they're the right material. Or maybe the Kart store ones are for special "racing" valve material...
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Old 10-08-2008, 08:24:01 PM
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Default Re: Valve guide bushings for aluminum Briggs Engines

I'm sure the rules have changed since I last built a racing engine,but the stock classes always used mostly stock B&S parts,the oil dippers and camshafts used to be the only parts that didn't need to come directly from B&S,so unless your buying parts that are specifically designed for modified engines,the valve guides should work ok.
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Old 10-08-2008, 11:12:52 PM
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Default Re: Valve guide bushings for aluminum Briggs Engines

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Originally Posted by Beanscoot View Post
Well I think in the past I used 660 bronze or phosphor bronze!, or even plain old brass if it was all that was handy. Anything's got to be better than cast aluminum, right?

Well I suppose I'll order a few long guides from the Kart shops or Goodson, and assume they're the right material. Or maybe the Kart store ones are for special "racing" valve material...
Goodson guides are made from C86200 bronze, wears well on stainless or ferrous stem materials.
-Aaron
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Old 10-09-2008, 02:18:21 AM
Beanscoot Beanscoot is offline
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Default Valve guide bushings

Yes, I'm just working on lawnmowers and rototillers and the like.
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Old 12-03-2010, 06:53:57 AM
bluejean bluejean is offline
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Default Re: Valve guide bushings for aluminum Briggs Engines

I have loose valves on a couple Biggs 5hp engines. Everything is stock. What do you suggest on valve guides. and where should I get them?
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Old 12-04-2010, 09:01:21 AM
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Default Re: Valve guide bushings for aluminum Briggs Engines

I'm sorry typo on the last post. It was suppose to say Briggs. I'm trying to replace the valve guides. What are the model numbers at Goodson? Goodson claims that they don't sell guides for Briggs and Stratton engines. Does anyone know other suppliers?
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