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Briggs & Stratton - broken push rod

This is a discussion on Briggs & Stratton - broken push rod within the Small Engines forums, part of the Tech Support Forum category. I bought my engone about 3yrs ago, have less than 40hrs on it. Model 446777, 26hp. I have no experience


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Old 09-04-2008, 05:31 PM   #1
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I bought my engone about 3yrs ago, have less than 40hrs on it. Model 446777, 26hp. I have no experience on fixing engines. I could do simple staff, but never worked on engines.

I lost a power on my engine and then find out one cylnder is dead. After opening the cover, I notice the aluminum rod push was breken into two pieces, and steel one was bented. I already ordered those parts + gasket.

My question is, having no experience, is it worth to ask someone else to do the work for $300 or I could try to learn it myself and do it. Should I open the whole engine to work on it, or one can just simply replace push rods from outside after removing the cover.

I have seen some good thread in this forum and learning a lot from all of you.

Thanks for your help.

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Old 09-04-2008, 07:22 PM   #2
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Sounds like your engine has had a pretty catastrophic failure - and whilst I hate to discourage anyone to "have a go" - if, as you say, you are not familiar with rebuilding engines - I fear this task might get away from you.

My real concern is that valve push rods do not generally fail of their own accord - so you need to find out what caused these to fail - as there is a risk there is far more serious internal damage to your engine.

Can I suggest you see if you can get hold of a copy of the engine workshop / repair manual and a full copy of the engine parts list / schematic views before you make a decision either way - at least you will be able to see what lies ahead of you and what, if any special tools you will need to carry out a repair / rebuild.

Others in the TSF may have some other ideas / suggestions but in the meantime - if it were my engine, I would speak with a specialist small engine repairer and try to get some inputs as to whether the engine is a fixable proposition at all. - I hate to bare bad news, but not knowing why the push rods broke / bent and if there is significant internal damage to the bore, cam and/or crankshaft - the engine may not be an economic repair proposition.

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Old 09-04-2008, 08:43 PM   #3
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Thank you for your advise. I spoke with Briggs and will call authorised dealer tomorrow to check the engine. Even though it has no warranty they did mention they may help with the cost if they find out engine had a problem and it was not created by me (like no oil, etc..)

If they do not cover, and friend of mine said it may be cheaper to buy another renuild engine than try to fix this one. As you suggested, he said
I could have serious internal damage.

Regards
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Old 09-04-2008, 08:57 PM   #4
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Great to hear that B&S might be prepared to assist.

Also - if internal damage proves to be serious - you might be able to get a "short engine" (that is a new block, crank and cam shafts, pistons & rings etc - all pre-assembled for you). All you do then is bolt on your old heads and auxiliaries. Not a small job - but much easier than an engine rebuild in toto. Still need a load of tools and some know-how - but if you can find someone to "watch over your shoulder" / give you some advise / direction - it might be a viable option.

Nonetheless - I would start pricing a new / replacement engine so you know what a reasonable budget for repairs would be - for my part anything more than 50% of a new replacement engine makes any repair out of the question on simple economic /warranty / future reliability grounds.

Pls keep us all posted on how you get on - am curious that B&S even hinted at entertaining some "out of warranty" assistance - does that particular engine have some hidden issues with its push rods / cams / valve assemblies
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Old 09-14-2008, 12:40 PM   #5
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I'd be curious to know how things with B&S went also. I have a similar engine. (Model 446977 27hp) I'm having a reoccurring problem with the push rods. I had what appeared to be a timing issue that I could not fix so I sent it to a local B&S maintenance provider who found that one of the push rods was bent. Supposedly nothing else wrong. I got it back and it ran fine for about two months until the lawn mower blades tangled (literally) with an extension cord that was laying in the yard. Figuring that a key was sheared and the timing was an issue again, and armed with the knowledge of that last repair, I checked the push rods, after checking the keys and timing and finding them ok. This time both push rods on the cylinder without the fuel pump were bent. I've ordered new parts and plan on replacing them on my own, but if B&S is having problems with those engines, I'd like to know. Thanks for the help.
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Old 09-14-2008, 02:36 PM   #6
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Certainly beginning to sound like there may be an issue with this engine's valve / timing / cam assemblies!!

Whilst I am not familiar with the particular engine - you and others are talking about failures occurring in an auxiliary drive not the crankshaft / main drive!!-

There is no load / impact bearing inputs on the cam shaft / valve assemblies etc. So even with shock stopping of the engine (although on mower applications - given they have long belt drives - even these shocks would be expected not to do too much damage to the engine) - it is hard to see that push rods would be damaged - If damage were to be done by a rapid full load stop - I would expect to see con rod / piston / crankshaft damage as that is where the loads are being transmitted.

Unless the timing went way out and the valve heads impacted the top of the piston on the upstroke (and you would certainly notice that kind of damage when you removed the head/s) - I can't see why push rods would bend / break - so maybe you are on to something and this engine's push rods are too "soft / weak" for the task.

Have B&S made any comment or changed the spec of the push rods??
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Old 09-23-2008, 05:17 PM   #7
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Pulled the head apart, on mine, today and found the problem.* Not sure why it's doing this, but here's the problem.* I replaced the intake push rod and hammered out the exhaust push rod (ordered one of each, but the exhaust one was backordered).* Turned the motor by hand and bent the exhaust push rod again.* Got looking and noticed that the valve guide for the exhaust valve was higher then the one on the other side.* This causes the top of the valve spring to bottom out before full travel.* Something's gotta give so the push rod bends.* Took the valve and spring out and tapped the valve guide back in and this looks like it might work.* The valve guide is very sensitive to damage and when tapping it in I created burrs around the edge which caused the valve to stick.* Working on fixing that now.* Again, I don't know what would've caused this pressed-in guide to move but this looks like the problem.* You can't buy just a new guide, you have to buy a whole cylinder head, with the guides pre pressed-in, at about $90, which is why I'm still working to fix the existing guide, although, I guess $90 is better then a new lawn tractor.* I'll let you know how it goes.
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Old 09-23-2008, 05:45 PM   #8
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Well done Bust-em
Looks like you have found the issue and maybe this is why B&S offered haikaa some out of warranty help.

Whilst you are doing all you possibly can on the "fix" front - I fear that given the heat / expansion contraction issues associated with cylinder heads - I am not sure how long the fix will last As once a "pressed fit" part starts to move it is hard to stop them repeating it unless some additional "mechanical restraint" can be added.

The problem is compounded as your engine is a twin and I assume both heads are identical - so the problem is likely to repeat with the other head at some time in the future

As this seems to be a not uncommon issue with this engine - maybe an approach to B&S direct (not thru their distributor) alleging their engine has a serious build problem and a request for some help (like exchange cylinder heads) would be worth a try.

B&S are generally regarded as good engines - so I would guess that they have instituted a "fix" (like improved valve guide mounting arrangements) for this problem by now - but aren't likely to offer it for free unless you make a fuss - and if it were me, I would be screaming from the roof tops until B&S agreed to some assistance as afterall - we are not talking about some "rinky-dink" 2 stroke - yours is a 27hp twin -& that is a serious industrial small engine
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Old 09-27-2008, 12:04 PM   #9
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Push rod problems can be due to valve adjustment. The intake is aluminum. When adjusting the valves check to see if the rocker nut has a torx set screw in the center. This is used to lock the nut down after you make the adjustment. Adjust valves when the piston is 1/4" past TDC due to the compression release arm on the cam.
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Old 10-21-2008, 02:59 PM   #10
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This thing is killing me!! I was happy that I was able to find and fix the problem, however, now that I've got everything back together, I can't get it to start. It cranks over, but won't fire. If the choke is on, it will backfire puffs of white smoke out through the air intake. I've checked the timing marks on the crank/cam shaft, and set the valve clearance at 1/4" ATDC. The shear key on the fly wheel is not broken and everything is still lined up. Without the choke on, it just cranks over and won't fire at all. Plugs are coming out a little wet and black. Any thoughts??
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Old 10-21-2008, 03:10 PM   #11
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OK - see if you do any good with a teaspoon of fuel poured into the plug hole - if this doesn't get it going - then I am afraid - that what you are describing has all the symptoms of a timing problem - even though you say you have it right - if you can't get the engine to start with a little fuel in the cylinder - then I would re-look at cam and ignition timing - sorry - I know it's a PiA

One last thing to check is ensure you have the plug leads connected to the correct plug - if unsure - just swap them over and see what happens

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