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Briggs valve guide moved, bent push rod

Posted by cbg640 (My Page) on
Sun, Jul 5, 09 at 10:05

My lawn tractor died the other day. I found a bent exhaust valve push rod. The valve will not push in since it looks like the valve guide is pushed out of place. The engine is a Briggs Vanguard 303777 1111-E1. Do I need a new head or new motor or can this be repaired? The engine has 586 hours use.


Follow-Up Postings:

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RE: Briggs valve guide moved, bent push rod

You need Walt!

Here is a link that might be useful: 303777 IPL


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RE: Briggs valve guide moved, bent push rod

  • Posted by canguy British Columbia (My Page) on
    Sun, Jul 5, 09 at 11:39

The normal procedure is replace the head but as mownie said, Walt may have a fix.


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RE: Briggs valve guide moved, bent push rod

That is very unusual for a Vanguard to do that. First thing I would do is look for a cooling problem around that head, plugged up cooling fins, etc.

I am not sure about Vanguard and I don't have a manual for it but I THINK they have replaceable valve guides. Best advice I can give is buy a B&S Service Manual for that series of engine.

I do have a fix for loose valve guides that I wrote for Intecs as they say you have to replace the head on them and it has worked for several people. I see no reason it would not work for Vanguard as well and you are welcome to look it over at least. Address below, put in proper format.

Walt Conner
wconner5 at verizon dot net


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RE: Briggs valve guide moved, bent push rod1

Note: As a follow up to above, in an email, cbg640 confirmed that the cooling fins were completely plugged off.

Walt Conner


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RE: Briggs valve guide moved, bent push rod

Please explain how the overheated head caused the bent push rod.
Thanks


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RE: Briggs valve guide moved, bent push rod

analogy:
Even back in the civil war, armies usta mess up a railroad by first prying a few lengths of track - then "cook" them over a hot fire. Rails would curl up like dandelion stems from the heat...
with those cooling fins plugged up that head got real hot. Hard on valves/pushrods that need to be straight.


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RE: Briggs valve guide moved, bent push rod

The overheated cylinder head expanded far more than the design limits could tolerate. The emtreme heat and expansion cause the valve guide to come loose from its bore in the head. As the valve guide got very loose it began to "climb out of" its bore, effectively "getting taller" than before. This extra tall valve guide will then prevent the valve itself from moving to the fully open position when the cam lobe lifts the pushrod to open the valve. The reason the valve cannot open fully NOW is because the collet on the valve spring bottoms against the too tall valve guide before the cam lobe has reach maximum lift. The result is the pushrod "buckles" under the very serious load that has been placed on it. The effect of the cam lobe pushing against the pushrod under these circumstances is analogous to standing a pushrod vertically on end and then striking it with a downward blow from a good sized hammer. That's what buckles the pushrod. Saying "bend" is OK, thats what it looks like. Buckling is actually what happens. I still say bend unless I am having one of these discussions :^)


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RE: Briggs valve guide moved, bent push rod

ATTN: Walt

Tried to contact you re your fix for loose valve guide in briggs 24 hp (446700). Ordered a new head but would like to repair old for a back-up.

my e-mail:

stave 'at' warwick 'dot' net

Thanks.


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RE: Briggs valve guide moved, bent push rod

The service procedure is in the manual 272144 dated 6/04, section 6 page 122.

The old guide can be pressed out and a new guide pressed in. Several special tools are listed to facilitate the pressing. A caution states - "Do not use hammer to install bushing". After installation, the guide requires finish reaming.

After repairing the valve guide, the valve face and the valve seat should be refaced.


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RE: Briggs valve guide moved, bent push rod

***"The service procedure is in the manual 272144 dated 6/04, section 6 page 122."***
The above may be 100% true, but it does not give the Walt Conner technique for dealing with a valve guide that has loosened and self ejected from the head. The Briggs manual gives the mundane, "perfect world" scenario of replacing a "worn guide" that has not self ejected. And the two scenarios require different procedures to fix. As has already been stated, Briggs recommends (eagerly) that you purchase a new head. Walt recommends you save some money.


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