diagnosing briggs ohv slow cranking

[38racing]

Many times it's just too much clearance on the intake but I've found bad grounding and worn starter bushing causing the same symptoms. I expect bad contacts in the starter solenoid might do it too. So I have a friend with the problem and I'm trying to convince him to go beyond the valves. So I just had a thought. Due to the compression release on briggs and other engines a compression test may not show the real compression . I know of a honda engine with release on exhaust valve and manual states to move rocker off the the exhaust valve to get real compression. So I was thinking of advising my friend to do a compression test. If he gets a high number like 100 or more then maybe it's a release issue but a number below 80? would eliminate compression as the cause of slow cranking?

[KE4AVB]

There is a difference between slow cranking and cranking problem caused by a fail ACR.

A disabled or failed ACR usually exhibits as too compression at near the top of the compression stroke by nearly stalling the starter or completely stalling it but starter spins fine until it hits this high compression. First you make sure the valves are correctly adjusted and then check for the decompression on appropriate valve. This can be either the exhaust or intake. On the 21, 28, 31, and 33 series with the 793880 and the cross flow heads this is the intake valve. Some other engines does this on the exhaust. If the bump is there then of course you look into cranking part of the engine and its electrical system.

This is why we are instructed to check for the ACR bump when adjusting the valves. This keeps us from doing unnecessary disassembly of the engine (it a non invasive check). This just like we should doing a leak down test on the 21, 28, 31, and 33 series when doing valve adjustments checking for a blow head gasket as we already have the valve cover off. It just another non invasive test that we can and should do everytime when we are checking the valve adjustments on these engines.

A slowing cranking engine would crank slower then normal though most the cranking cycle with the starter hanging up at the compression stroke. I just had one yesterday where the engine started cranking slower than normal and stall at the compression stroke. It was low voltage caused by a defective battery. Of course I checked the battery first using a meter. But anything can cause slow cranking. Things like worn bushing and brushes, shorted windings, and major voltage drops caused bad connections. I repaired a Craftsman last year that had problem cranking that turn out to a be internal problem with a battery cable terminal. Upon Visual inspection it looked fine but there was massive voltage across the connection. I just cut off the end and hydraulically crimped a new terminal on which resolved the problem. Doing voltage drop tests will find these bad electrical connections. BTW starter solenoids do develop burned contacts that you can't physically see without taking them part but it usually destroys the solenoid doing so. Again voltage drop testing finds these burned contacts.

Customers can evasive too when it comes to reporting problems. Example: Initially the customer wanted to know how much labor I would charge to install a PTO clutch. Which I gave a 1-2 labor estimate. Here I just received the CC mower with the fail PTO clutch. At first I was told it was just a clutch replacement but when mower arrives they also noted it needed a drive belt and put a $500 limit on repairs. Well I just completed the inspection late yesterday. What a mess. Yes the PTO is bad since the broken drive belt wrap around the engine pulley and pulled the wires out. Some idiot (I could type worst comments) found the engine pulley stuck on from rust. Instead of just unbolting the engine so they replace the drive belt (which I done many times) they proceeded to destroy the engine pulley. They even took die grinder with a cutoff wheel and sliced off one of the retainer ears leaving sharp edge that will destroy any new belt installed. As normal part of my check I found all the idlers needing replacing. Of course I need to pull the engine now so I can remove the engine using pullers and heat. And I will need to repair the frame replacing the retainer ear. The estimate stands at $650 so I just the old PTO back on and the deck until either I get approval and they pick the mower back after paying the estimate fee. Strange I got everything in stock except the engine pulley.

Of course I ran into one my pet peeves about customers and that is having voice mail accounts not setup so you can't even leave a message. Boy that is irritating.

[Arkie]

Many times it's just too much clearance on the intake but I've found bad grounding and worn starter bushing causing the same symptoms. I expect bad contacts in the starter solenoid might do it too. So I have a friend with the problem and I'm trying to convince him to go beyond the valves. So I just had a thought. Due to the compression release on briggs and other engines a compression test may not show the real compression . I know of a honda engine with release on exhaust valve and manual states to move rocker off the the exhaust valve to get real compression. So I was thinking of advising my friend to do a compression test. If he gets a high number like 100 or more then maybe it's a release issue but a number below 80? would eliminate compression as the cause of slow cranking?

Yes, slow cranking or engine crank stalling at the compression stroke is one of the more iffy ones to sort out. Trying to determine if it's mechanical or electrical (or both) and telling someone else how to test for such.

What is the Model number of his engine?

I've got a friend that sells starters and he sells several small engine starters and he gives me the trade-ins. He says he casually asks them if they have checked the valve lash when they insist on a new starter. He says they usually say no, why should I check the valve lash, it's runs good when it starts, I'll try that next maybe and they buy the starter.

About 80% of them starters are good starters that he gives me.

[38racing]

He messaged me last night about because his brand new high cca battery didn't solve the problem. He said intake was about .004 but before I told him about the 1/4 past tdc so don't know if that's accurate. If so it's in range. He sent sent a grainy video of his hand turning it and I think I see the bump. He feels that with the plug in its even too hard too turn by hand. Given that he says it turns real easy with plug out I ruled out pto clutch binding.

[KE4AVB]

Always hard to troubleshoot remotely.

[Arkie]

Some electrical tests. (Just few tips)
I've got all kinds of electrical testers and high amp DC clamp on ammeters so as to analyze cranking voltage and starter draw amps, but I sometimes just take a good set of Automotive jumper cables, and do the following connections in this exact sequence, Remove the neg battery terminal cable and leave it disconnected if using the machines bat, (I sometimes just use a stand alone battery or a portable battery pack) connect the automotive pos jumper cable to a known good bat pos terminal and then to the starter lug terminal, (make sure this connection is secure)
then connect the neg cable lead to the neg bat terminal and THEN make the last connection to the frame. REASON for the last connection to the metal frame is this is where sparks are going to occur and they will be away from the battery and also no sparking and arcing at the starter stud copper nut and it's threads.

This bypasses all the electrical connections, solenoid, frame ground cables. If I get a good crank then I know I have an electrical issue. To see if it's the machine ground cable connections use only the neg automotive jumper cable for connection to the engine block and the battery and crank test with the machines key switch. Using a good set of automotive jumper cables can save a lot of time at first instead of using electrical testers and especially if proper electrical testers are not readily available.

If I get a weak crank doing this I then look at mechanical issues such as valve lash, and if valve lash is ok I do a starter amps draw test and if amps are weak and bat voltage good I suspect starter brushes, if amps high I suspect bad bushing and or starter commutator (battery is capable of high amps but starter dragging) if engine compression is within reason. If battery amps are high when cranking do a unloaded starter amps draw test.

On a small engine if I can see the starter bendix drive end of the starter I do a wiggle test of the upper bushing. If any noticeable sideways slack the bushing is gone (needs another starter whether this fixes the total cranking issue or not) and the commutator may be rubbing against the field magnets or field coils.

Also bad electrical connections generate heat. A careful quick to the touch feel test can detect a bad crank connection. Be aware that a bad crank connection can fry meat. (very hot)

[KE4AVB]

Let's get out the BBQ sauce...

[Arkie]

Let's get out the BBQ sauce...

Yep, not a good thing when you grab on to a heated bad electrical connection and smell and feel your own skin burning fast and it will usually be your main default fingers every time that you need to hold wrenches. (thumb and pointing finger) AND others point and laugh at the electrical troubleshooting genius.
You will not forget this type of fingers burnt the next time you are carefully doing the feel for heat test.

[38racing]

Let's get out the BBQ sauce...

Yep, not a good thing when you grab on to a heated bad electrical connection and smell and feel your own skin burning fast and it will usually be your main default fingers every time that you need to hold wrenches. (thumb and pointing finger) AND others point and laugh at the electrical troubleshooting genius.
You will not forget this type of fingers burnt the next time you are carefully doing the feel for heat test.

I had a starter solenoid or keyswitch stick once and was trying to unhook the battery cable to stop the cranking. Hot for sure.

[KE4AVB]

Hey Arkie ever had one you finger to get a third degree from an electrical charge? It happen to me when working a homemade linear power supply. I drained the caps but didn't leave the jumpers in place. I had over 600 vdc to go through my finger. Of when a returned the linear the safeties resistors were in place so would not happen to another tech. A pain lesson to keep jumpers in place unless the safeties are present.

The burn was all the way to muscle and took several months to heal.

Now that is one way to fry a ham. (Amateur Radio Operator here)