Troubleshooting 18.5 BS Intek v-twin

Hi. I have an 18.5hp, B/S Intek V-twin on a craftsman mower. Mower model is 917.270760. Engine # appears to be YBSXS.7242VF 274729.

It's been running a bit rough and showing some oil leakage around one of the valve covers.

While my daughter was mowing with it over the weekend, it quit on her. She said it got pretty loud and started smoking so she shut it down. I am able to start it, but it has hardly any power. It's doing a lot of popping. Spark plug on one side looks ok, but the other looks severely loaded up - dry with a lot of build up on it. I thought it might only be running on the one cylinder, so I disconnected the plug wire from the fouled plug - but the motor would not start - so I'm assuming it was actually running on both.

I think it definitely has major issues. My suspicion was a blown head gasket or broken rod. With it not wanting to start without both cylinders, I'm thinking more head gasket.

My question is - Is there any way I can determine if this is the case without going ahead and tearing it down? Any other ideas on what the problem might be? This is a fairly old mower, probably 11 or 12 years - so I'd probably not invest too much into it, but if it is something I can fix - I'd like to keep it going.

Thanks for any help you can offer....
Steve

 

You might try a compression test first. Did it knock at all before loosing power??

 

Was it out of oil? Sounds like it may have thrown a rod. Check for compression on each cylinder. If none on one, stick a drinking straw in the plug hole and turn the engine and see if you feel anything pushing the straw back out. If not, the piston isn't moving (it threw a rod).

 

Thanks for the replies.

No - it wasn't out of oil. Dipstick showed full after the ordeal.

Will a regular automotive compression tester work for this, or do I need to find one specifically for this type of engine?

If it has thrown a rod, is it practical to attempt a rebuild or scrap it?

Thanks again for your help,
Steve

 

@mowerdude -

I wouldn't say it had a real knock before any of this, but it definitely has one now.

It did have a tapping sound. I had intended to get in and adjust the valves. Hopefully not too late...

Thanks,
Steve

 

@ Hammer Time,,,yes a regular compression tester will work. If a rod has broken repair will be quite high. Depending on the damage. If block is not damaged and if crank has no damage, which I dought. If it was knocking the crank is propably junk!

 

You don't need a compression tester, just put your finger over the spark plug hole and see if compression blows past your finger.

 

Any amount of compression will blow your finger away, if the compression is below 60 lbs you have serious problems. If compression is in the 140 range all is well with rings and valves. But you are looking for a knock,,,,,,pull pan and inspect! It almost sounds like to me like the engine may have broken a ring or a piston, espically when you say one plug was or is loaded up,,,,OIL??? Where is it coming from,,,,pull that cylinder head and inspect, and inspect the cylinder wall for scoring! Gotta be a reason for the plug being loaded up.

 

@Mowerdude -
Sorry to have to ask, but what do you mean when you say to pull the pan & inspect?

I've not yet been able to get a compression test. I do feel pressure on each cylinder with just the "thumb test". Also - I've tested to verify that each piston is cycling - so apparently no broken connecting rods.

I was able to start the engine again last night, and it actually sounded healthier - good throttle response where before it was really sluggish to rev.

The knock (or popping) seems to be coming more from the left side. With the breather off, it really sounded like it was coming from the intake. Don't know if that means anything or not.

Hope to pick up a comp tester today. Can't find one to borrow, so it looks like I'm buying one. Always good to have a reason to buy a tool. Are we certain a standard tester will be sufficient? Is there a possibility I'll need to do a leak down test?

Thanks,
Steve

 

Also - Is there a good manual that anyone would recommend for this thing? Online would be great, or a book that's typically available?

 

You found out if it's blown or not, so I don't see a real need to go buy a compression tester. Since the popping is coming from the intake area, I'd be looking at the valves and clearances.

 

Just do what Cheese says ,,I don't know nothing!!

 

Okay - turns out I was able to get a compression tester on loan from my local AutoZone. Their website indicated they did loan them, but when I called the clerk said they didn't. Went in to buy one and the guy said they DID loan them. Guess it just depends on who you talk to.

Anyway - about 120 lbs on one cylinder, 165 on the other.

So - pulled the valve covers. First one - everything looks ok. Not so ok on the other side. the push rod on the upper valve looks to be pretty bowed. Supposed to be fairly straight, right? And I can't even find the rod for the lower one. Guessing this isn't good.

So what's my next step - tear it down and check for damage? Is there any good manuals (paper or online) available to guide me through a teardown & rebuild? Is there much chance that this can be salvaged? Like I said, I can't even find the lower rod so far.

Thanks for all your help. You've all been right on the $$ so far.

 

I've seen that happen. Take the engine off and open it up to get the push rod out of the oil pan. I think the valve guide came loose and made the valve stay closed, causing the push rod to bend or break (I think the last one I did actually collapsed within itself). Then it falls out of place and into the engine. It's not a hard job to fix. Check the head for damage (valve guide sticking up inside the spring more than the other one). If the head is damaged, you'll need a head, head gasket, and sump cover gasket. With an impact gun, parts in hand, and a manual, it is a fairly painless job that can be done in a few hours.

 

OK. Where is the best place to get a manual? Are these ever available online?

 

Yeah, I think briggs pretty much removed all the repair manuals that were online. The only thing you should need is the head bolt torque and sequence. I'll look it up if you want. I should remember, but I never can.

 

I was able to find a manual online at Scribd. So far pretty helpful.

I'm to the point of pulling the flywheel. Anyone have any tips on how to pull the flywheel without the official B&S holder and puller?

My immediate problem is getting the nut off. I'm not able to hold the flywheel tight enough to be able to break the nut loose with a breaker bar and socket. I have a 3/8" impact gun I intend to try, but I'm doubting it will have enough umph to break it loose.

Thanks for any ideas you can offer.

 

You don't need to pull the flywheel. Just remove the bolts holding the engine to the frame and the other wires and stuff that go to the engine.

 

I've finally gotten back to working on this. Got the engine off and pulled the oil pan off. The missing rod dropped out with the camshaft. It was fully intact, but had about a 45 degree bend in it about 3/4" from the end.

Everything appears to be ok, except for the 2 bent push rods.

Hoping to order parts tomorrow. Planning to just replace all 4 rods. Of course replacing all gaskets. (Head, oil pan, valve cover) I'm seeing nothing visibly wrong with the tappets. Should they be replaced anyway?

Also - I'm not seeing anything obviously wrong with the valves. all appear to operate. Nothing stuck or marred up. However, since I've got it all apart, would it be wise to replace the guides, seals, or do anything with the valves themselves?

Same thing on rings. Any point in re-ringing?

Again - thanks for your help!

 

No need to replace valve tappets, make sure there is nothing wrong with valve guides before putting that head back on,,or are you just going to replace it. If the valve guide is sticking out it has moved and the rocker arm will hit it and you will bend push rods again! You need to determine what bent the push rods,,what failed!!

 

If it wasn't smoking, no point in messing with the rings. If it ain't broke....
The push rods bent for a reason. I think it would pay to figure out what so that you don't put this thing all back together again, crank it up, and wind up having to do the job all over again. I'd take the valves out for sure and clean them and inspect the guides.

 

Have all my parts ordered. May see them tomorrow. Went ahead and ordered valve seals, spring retainers & keepers too.

I can't find anything wrong with the valves, so going to keep the old ones.

Can you tell me how best to clean them up for reassembly?

 

A bench mounted grinder with a wire wheel works well. Some coarse steel wool would be okay. The main thing you want is to clean and polish the stems.

 

So really no need for lapping the valves? Just knock the crud off the face & polish the stems as much as possible?

Also - for this engine, I'm seeing no valve guide other than what is machined into the head. Each intake valve has a rubber seal, which I'm replacing. Other than that - just valve, spring, retainer & washer. If this sounds bizarre I can post a pic of the exploded parts view so you can double check me.

Just got a call while writing this - parts are in. Too late for tonight, but will pick up tomorrow. Hope to start assembly tomorrow night.

Thanks again for the help,
Steve

 

I'm going ahead and attaching a shot of the head diagram for this. Am I missing an actual valve guide, or is it machined into the head itself?

 

Yes, you should lap in the valves if you have the tools. The valve guides should already be in the head if you bought new. If there is no guide the valve will slop around in the hole.

 

The guide is part of the head, not available separately. It won't show on the diagram because it's not serviceable. If it comes loose, you toss the head and get another. What happens is the aluminum head gets overheated because of lean running conditions (clogged carburetor) or debris in the cooling fins. The aluminum expands far more than the bronze valve guide that is pressed in. Then as the valve is moving, at some point in time, the guide moves with it and sticks (usually it moves out toward the valve cover side of the head when this happens, but sometimes it moves to the other side) and this holds the valve open or closed, depending on which way it moves. If the guide moves to the valve cover side (holding it closed), then when the camshaft pushes the pushrod back around to open the valve, it can't because the guide is stuck out, holding the valve closed by hitting the valve spring retainer. So, the push rod bends, falls out, and you lose power from that cylinder.

If both valve guides are correctly in place, another cause for a valve sticking open is varnish buildup on the valve stem. It is usually a tan, almost gold colored varnish over the silver steel valve stem. I usually see this on engines that have been running with old gas in them. This varnish can cause a valve to suddenly stick and bend the push rods. Sometimes it will cool off and allow the valve to work again, creating a mystery (bent pushrods for no apparent reason) as you've described here.

 

I've been working on this - slowly but surely. actually have gotten the block back together, heads re-assembled and put back on.

I just happened to check out a video that showed a similar engine with a valve guide that had slipped and done the very same thing this one did. Bent the intake push rod, chewed up the exhaust rod & dropped it in the pan.

Went back out and made ANOTHER final inspection. Sure enough, the exhaust valve on one one side doesn't travel nearly as far as any of the others.

Going to pull that side apart and re-examine. As I understand, if that valve guide has shifted outward, limiting valve travel - it's over - no fixing possible. Replace the head and go on. Is that correct? If so, I'll get it ordered today.

 

Correct, just replace the head if that's the case.

 

OK. Got this thing reassembled and back into the mower. Believe I have all electrics and fuel connections made. Carb is getting fuel but will not even try to start. Cranks & sounds fine. Tried an old spark tester I have, and it appears to be getting no spark on either cylinder.

Any ideas for what to check? Was very careful with aligning timing marks. Anything that I may have left undone that would allow it to crank but not fire?

 

Check the kill wire to the coils. If it is shorted, it will not fire. Look where it goes behind the starter as this is a common place for it to get pinched.

 

Well. We have it running. Last night I pulled the kill wires off the armatures. Still got nothing. Tried it one more time this morning & it cranked right up. I am having to jump directly to the starter. Bad solenoid?
Didn't have time to mess with it much, but was trying to run wide open when I took choke off. Hoping just linkage issue.

 

Still wrestling with the carb & governor linkages. Can anyone describe to me how the springs are attached in this setup? The parts diagram shows them, but not where they're hooked. There's one large spring and one small.

 

This shows the location of both springs. The other end of the big spring connects to the long governor arm in the slotted hole. The other end of the small spring connects to the hole in the little tab just under the left side of the big spring in the pic.

 

Cheese - Thanks for the pic & instructions. It couldn't be any clearer, but I'm still having problems. It seems like something has to be backwards, upside down, or inside out.

I can't get the linkage to adjust in any way that closes the carb down to a normal idle speed. What I'm seeing is the carb control ties directly to the eye on the end of the governor arm. And no matter how I adjust the governor - high or low, the arm is being pulled down by the springs between it & the throttle cable mount. I can put the arm up as far as it will go to start with, but the spring tension pulls the arm, and the carb valve nearly to wide open.

Does this sound right? Am I missing an adjustment detail? Or possibly missing a part? Should there be a 3rd spring pulling the governor arm up?

Sorry to be so dense. I'm really close....

Thanks for your help....

 

Did you get the governor installed correctly inside the engine? There are videos on youtube that cover governor adjustment on a briggs twin intek engine like yours. Basically, you loosen the governor arm clamp bolt, set the carb to wide open, turn the governor shaft to wide open, and while holding them both in the wide open positions, tighten the pinch bolt.

 

Yes sir. I think we probably saw the same video. Hold swivel and shaft wide open, then tighten the arm. Also tried it complete opposite. I believe the governor is correct inside. I've actually had it running and even mowed with it, but the knew throttle wasn't quite right. Almost seems like if the rod between the Carb and governor arm was 1/4" longer, it would have it near the correct idle position.

I should have some time to fiddle with it tonight & maybe reinstall the whole setup. Thanks again for your help.

 

I didn't watch the video, but if you set it exactly as described, it will be right. If it still doesn't run right, don't adjust the governor to compensate for it, it's another problem with something else.

 

Well - still dealing with the throttle/governor issue. The thing runs great, I've actually mowed my complete yard with it - but have to be adjusting the throttle almost continually. Just a hair too much throttle, and it just start racing. A little too little, and it won't keep up bog down under any load.

I can't help but wonder if I failed to get something set up correctly internally on the governor. The governor shaft itself has maybe a third of a revolution of actual range - lock to lock. Physically, it appears the governor arm is doing what it should.

Is there any way I can tell whether it's a carb or governor issue? I'm about to give up and take it in to the shop, but having successfully done such major work, I hate to not be able to resolve this. Would like to get it to the point where someone else can do the mowing though.

 

If you reach down and move the throttle wide open with the engine running, do you feel the governor try to pull it back? If not, something is wrong with the governor and it's either not set right or it's out of place in the engine.