24HP V-Twin B&S - Fault driving me CRAZY!

[Neo7]

Bert thanks so much for all your additional thoughts. Here's my run down on those...

I will still go with a cam defect.
The figures quoted with the tape test definitely show one cylinder lagging behind the other.
As the cams are pressed onto the shaft on a spline I am guessing , and this is a wild guess yours are out of time.

Yes but in hindsight the test really didn't compensate for human (me!) error and the minute differences between the adjustments on each rocker. I don't believe we can beat a high accuracy (digital vernier calipers) measurement directly on the cam lobes and the relative positions of the peaks of each lobe. The order of individual cams positioned on the shaft are Exhaust 1, Exhaust 2 then Inlet 1, Inlet 2. So I've just measured the straight line distance between the peaks Exhaust 1 to Exhaust 2 as 14mm and Peaks Inlet 1 to Inlet 2 as 14mm.... I also checked each cam for play on the shaft and the main gear play on the shaft ...there's no play on either. If you could see the cam you'd see it's in excellent condition .... Remember the fault has been there for quite a few months now so if the cams lobes are rotating on the shaft the damage/wear would be easy to see by now.

If the local B & S dealer is a nice guy take your cam and ask him to compare it to a new one.

My closest B&S stockist (that would stock a cam) is 50 miles away and they are really an online store and not so helpful.

Check all of the pushrods for length & straitness.
Also check that the alloy ones do not have a worn ring & are hanging on the shoulder of the worn area.
Also double check the valve spring length and spring rate.

Checked the rods once again. The two Ali ones are identical in length and the two Steel ones are identical in length. Both Ali ones are 0.5mm longer than both Steel ones. I rolled them all on a sheet of glass checked the ends and they are all in excellent condition.

Also double check the valve spring length and spring rate.
Cheap & nasty way is to put a bathroom scale on the deck of a bench drill ( a press is better ) then compress till the spring is 10mm shorter.
Read the "weight" shown on the scales. They all should be within 10% of each other or better.

This was a great test and here's the results from my Digital Bathroom Scales in my Drill Press ....
Spring 1 - 10mm Compression = 12.5Kgs - 20mm Compression = 23Kgs
Spring 2 - 10mm Compression = 12.5Kgs - 20mm Compression = 22.6Kgs
Spring 3 - 10mm Compression = 12.7Kgs - 20mm Compression = 22.5Kgs
Spring 4 - 10mm Compression = 12.3Kgs - 20mm Compression = 22.9Kgs
I should minus the weight of the 2 block I used on the scales (maybe 1 Kgs) but the resultant is the same.

Height were all within 1mm of each other and max compression was 22mm for all 4 springs

This kinda the Faultless Engine with Problem! :laughing: ... But please don't give up on me guys ... someone is gonna crack this for sure :thumbsup:

We've hit Page Seven ... and Seven's my lucky number

 

[Boudreaux In Eunice La.]

I sure wish that mower was in the front me..... I am going to read the whole thread again tomorrow.....

 

[Neo7]

I sure wish that mower was in the front me..... I am going to read the whole thread again tomorrow.....

Should I post you an Airline ticket :laughing: .... Thanks Boudreaux :smile:

 

[Neo7]

Tape Test....Left-InlCloses compared to Right-InlCloses - Right Closes Later 13mm

Measured height of rod ...
Left-InlOpen - 18.2mm
Right-InlOpen - 16.8mm

Hmmm.... am I missing something??? ... If I remember correctly the Right Inlet is closest to the top...What if the top cam bush, built into the inside of the case, has worn elliptically?... need to triple check things tomorrow.:confused2:

 

[Neo7]

Alas NOoooo! .... Cam bush seat is in great condition. I even tried pushing in the Tappet for the Left (1) Inlet (The 1st/Top Tappet) Tappet but the cam and bush stood firm.
I also position each lobe at its high point and measured the Tappet ball seat to the flat (gasket) edge of the cylinder. All 4 measures +/- 0.3mm within each other.

I can feel my head starting to spin :confused2: :laughing:

 

[Ronno6]

Without taking the time to review the thread in its entirety,
have you tried new spark plugs??

Plugs can cause some weird situations.........

 

[Neo7]

Agreed and yes plugs have been replaced. :smile:

 

[bertsmobile1]

Bert thanks so much for all your additional thoughts. Here's my run down on those...

Checked the rods once again. The two Ali ones are identical in length and the two Steel ones are identical in length. Both Ali ones are 0.5mm longer than both Steel ones. I rolled them all on a sheet of glass checked the ends and they are all in excellent condition.


This was a great test and here's the results from my Digital Bathroom Scales in my Drill Press ....
Spring 1 - 10mm Compression = 12.5Kgs - 20mm Compression = 23Kgs
Spring 2 - 10mm Compression = 12.5Kgs - 20mm Compression = 22.6Kgs
Spring 3 - 10mm Compression = 12.7Kgs - 20mm Compression = 22.5Kgs
Spring 4 - 10mm Compression = 12.3Kgs - 20mm Compression = 22.9Kgs
I should minus the weight of the 2 block I used on the scales (maybe 1 Kgs) but the resultant is the same.

Height were all within 1mm of each other and max compression was 22mm for all 4 springs

This kinda the Faultless Engine with Problem! :laughing: ... But please don't give up on me guys ... someone is gonna crack this for sure :thumbsup:

We've hit Page Seven ... and Seven's my lucky number

Actual numbers are no help to me cause I don't have access to the Briggs dealer portal & I ain't about to stock $ 20,000 worth of B & S parts just to get access.
What is important is they are all the same , well close enough to being the same.
Spring rates on mower engines are not that important as they are slow reving but if one was way out it would explain the bad running.

 

[Boudreaux In Eunice La.]

I have read and reread all the post's and I am still trying to figure this out ......I would like to see the heads in some pics without the springs on them..... Both sides ...........Check the heads for flat by putting 200 grit sandpaper or finer on a dead flat surface then mark the gasket area with a Sharpie and rub the head in a figure 8 motion for a few minutes,,, Look at the surface and check for flat......

A bad intake intake manifold will do this also ...... They do warp and get out of shape....... Causing an air leak that you will never find...... In some cases ....... That will act like a bad carb......

In post #21 you said you had a huge backfire...........That is cause for a partially and I mean a very small sheared Flywheel key.... It don't take much for a key just a few thousands off to make a engine run bad ........ I know first hand on that SCHITT..... What I thought was a good key was A BAD key.....

Let us know Mon Ami ~!~!

 

[Neo7]

Thanks for staying with me on this Boudreaux :thumbsup:

I would like to see the heads in some pics without the springs on them..... Both sides.

Ok will post up some photos soon.

Check the heads for flat by putting 200 grit sandpaper or finer on a dead flat surface then mark the gasket area with a Sharpie and rub the head in a figure 8 motion for a few minutes,,, Look at the surface and check for flat.

Ok will do this. Just need to buy a 200 Grit Sanding (sticky) pad ... is 120 Grit far too coarse?

A bad intake intake manifold will do this also ...... They do warp and get out of shape....... Causing an air leak that you will never find...... In some cases ....... That will act like a bad carb.

Thanks for reminding me about the manifold .... A trick I've used with motorbikes is to spray an aerosol (like degreaser) at the gaskets while the engines running. If the manifolds not sealing it would suck in the degreaser causing the engine to half stall for a second. When I replaced the carb I used a gasket seal on all the gaskets (head ports to filtered air intake shoot) and the next day I did my test with the degreaser all over and around the manifold... It passed with flying colours! .... I'm not saying it can't be the manifold but I really want to prove this before purchasing a new one. So when I have the engine assembled and running again I'll definitely reevaluate this.

In post #21 you said you had a huge backfire...........That is cause for a partially and I mean a very small sheared Flywheel key.... It don't take much for a key just a few thousands off to make a engine run bad ........ I know first hand on that SCHITT..... What I thought was a good key was A BAD key.....

I'm curious about this one .... My Key was not marked or damaged when a checked a few weeks back. So are you saying a key can be thinner than it should be? ... Worn so gradually that it looks polished on the sides?.... How tight should a key be in either keyway (flywheel or shaft)?


All the very best.
Neo