Model YTH 18542 Mandrel Assembly

[ILENGINE]

Considering the shear number of the 21, 28, 31, and 33 the failure rate is quite low. And for it is mainly the 31 series with a few 33 series. Kinda strange that I don't the same failure in the 21 and 28 that uses the same camshaft. THe only repeat failure I had was the cheap Chinese knock off I tried.

I noticed on the latest 793880 camshafts that an engineering change has been made. They have hour glassed the ACR pin so that the lifters are now contacting it less.

You are right about the 21 and 28 series engines. Those engine have been around since the early 1990's and a lot are still running the original cams and several that have never had the valves adjusted outside of the occasional head gasket. When the 31 series came out in the early 2000's is when the valve adjustment issues, and the blown head gaskets, and the camshaft ACR issues really intensified.

 

[TobyU]

Considering the shear number of the 21, 28, 31, and 33 the failure rate is quite low. And for it is mainly the 31 series with a few 33 series. Kinda strange that I don't the same failure in the 21 and 28 that uses the same camshaft. THe only repeat failure I had was the cheap Chinese knock off I tried.

I noticed on the latest 793880 camshafts that an engineering change has been made. They have hour glassed the ACR pin so that the lifters are now contacting it less.

Yes, percentage-wise it's quite low and probably quite acceptable to their company decision makers. But numerically, it's still too high!
In fact, anything over one or two is too high because they didn't have this problem before and then they started having the problem SO should have fixed it.
They didn't -at least not for a long time and maybe they still haven't.

It's hard to trust Briggs, thinking a new part may have improved the design because they have a history of changing their part numbers all the time even though it's the exact same item and not improved.

I don't have a lot of faith in their replacement parts because I've seen too many almost brand new Factory ones fail.
It doesn't seem to matter how young or old the thing is.
I've seen them fail under 10 hours and seen them fail anywhere up to 100 hours without any rhyme or reason.
Then I've seen some be closer to 200 hours when they fail.
Most mowers in my area don't get over 230 to 260 hours on them because the people end up replacing the entire mower by then because going from the dates of manufacture and the hour meters on the mini mowers I serviced over the decades, they tend to put under 25 hours per year on their mower with only a few getting close to 35.
I routinely did the math and it ended up being under 25 hours per year. So somewhere in that 12 to 14 year range with still quite low hours on it, they would end up upgrading to a new mower.

When I purchased the last camshaft I did notice Briggs had changed this particular one from there standard six digit part number to a part number much longer with a lot of nines in it from what I remember.
I thought I would give them the benefit of the doubt and hope they had changed this part along with a numbering system so I made sure I got one of those and not one of the other replacements with the six digit number that were readily available.
Don't know if that helped or not and I didn't actually notice any difference on this particular part versus the old one when I installed it like you mentioned on the redesign.

I will maintain it's a crap design though and way too delicate.
Mostly I will blame the little plastic bushing because they don't believe plastic has any place inside of any engine.
I can't think of an application where I would rather or just have to put plastic inside of an engine because there should always be another material that can be used and I feel that in almost every application the other material would be superior.

The pin of the spring are delicate enough but I think they would manage if it weren't for the plastic bushing but I know for a fact we could redesign and improve this system without a whole lot of effort.
Fact that they haven't done this ticks me off.

So there are way too many because even one is way too many.

 

[TobyU]

I am curious of what the repair failure of the OEM Briggs camshafts are . Has anybody experienced repeat failures with the same customers mower. Or is it more of a "one and done". It seems like a lot of the ACR fail and lots of camshafts get replaced but in the large scheme of things I wonder what the overall failure rate is.

It's certainly low percentage wise on the failures but numerically it's way too many as I mentioned in another post.
If I had to estimate, I would say it's well under 2% of all these similar Briggs engines and likely closer to a half of a percent.
That is quite acceptable by most company standards of quality control etc but still this leaves hundreds and hundreds of them in any large market and I feel that's unacceptable.

I mean, I could literally fix one of these camshafts myself to wear it would be much more durable than the factory design and likely never fail.

I saw a thread one time where somebody was doing just this I believe.
Simply welding the pin into the hole in the camshaft I believe would solve the problem.
I don't have one in front of me to play with now but I don't believe the pin itself has to move and if after it was assembled, the pim was welded into place, it wouldn't need the plastic bushing and there wouldn't be the potential for the slop that allows things to get a place and then come apart and get broken.

But of course even if you fix this problem you have the other smaller problem of the camshaft lobes becoming loose or spending or whatever like I've seen a few times.
Another lousy, low quality design so they can save some money in the assembly process.
If they're going to press lobes onto a camshaft, which shouldn't be done in the first place, they could at least take some other precautions with standard machine shop procedures like drilling pinning it so it can't turn.

 

[ILENGINE]

It's certainly low percentage wise on the failures but numerically it's way too many as I mentioned in another post.
If I had to estimate, I would say it's well under 2% of all these similar Briggs engines and likely closer to a half of a percent.
That is quite acceptable by most company standards of quality control etc but still this leaves hundreds and hundreds of them in any large market and I feel that's unacceptable.

The basic acceptable failure rate is around 1% for all industries, which includes appliances, tractors, automobiles, computers, etc.

 

[TobyU]

The basic acceptable failure rate is around 1% for all industries, which includes appliances, tractors, automobiles, computers, etc.

Yes, and often even slightly higher than that is acceptable. Even three to four has still gotten a pass for an entire batch in many situations.
Different companies do it in different ways. Sometimes if they had a failure rate of over a certain number in a whole run of production, they would pull that entire batch out and go back in and check the actual problem areas or replace a board etc.

It doesn't matter what the numbers are in this because that's not what I was discussing but rather that because there are so many made, the percentage, even being small makes for a very large number of them.

This number is completely unacceptable in my opinion.

The fact that they didn't change it close to immediately is also unacceptable.

My opinion and comments on this are further supported by the fact that other manufacturers and other engines have not had similar problems repeatedly and for decades. Lol
You never hear of a Kohler camshaft ACR failure even though anything is possible.
So for me, even if it's only half of that 1% of industry acceptance (which I believe I used in one of my estimations) even being twice as good as the industry accepted standard in most things... It's still completely UNACCEPTABLE to me.

They're also is the extra consideration in my determination of these things whether it's something that's just annoying but quick and easy to fix versus something that's internal engine and requires extensive time, effort, labor to fix.
Completely unacceptable!
1% be damned...

 

[bertsmobile1]

Goes like this

Some mental giant with 15 university degrees decided that B & S could make more money if they old off all of their manufacturing plants and just assembled engines from bought in parts where they could screw down the price with each new delivery
Once having done they they lost the ability to make the small but significant changes that failures point out need to be done .
Having gone back to the "core business" they are now stuck and will vanish from the face of the earth in the near future .
I buy my cams direct from the factory in China that makes them and have never had a problem other than having to buy them in larger quantities than needed
Back in the good old days B & S had the capacity to check parts orders for quality.
Now like every other business the "check" is done by the customer and B & S gets discounts if the number of reported failures exceeds a specified value .

I no longer fit B & S engines as there is no point in doing so as B & S Australia are pathetic when it comes to stocks of spare parts so I fit either Kawasaki or Loncin .
Both are substantially better built engines and both have a more reliable parts supply .