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I recently rebuilt a 17hp Intek engine for a riding mower: 31G777-0290-E1. The connecting rod had broken, which also broke the camshaft & oil slinger/governor. I had purchased a new rod & ring set for another engine, and took the other damaged parts from other engines. I have rebuilt maybe 5 or 6 engines before (all "L-head"), so I feel comfortable with my abilities. After putting the engine back together with new rings, etc., the engine was hard to turn over on the compression stroke. Got it started, ran good for 3-4 minutes, shut it off. Tried to re-start, again hard to turn over on compression stroke. Tested starter (almost new starter) & electrical - all tested good. Looked at several posts (some by Walt) about valve adjustment & compression release. Adjusted valves to 003 intake/005 exhaust 1/4" past TDC per Briggs service manual. Compression release seemed to be working correctly. Since I couldn't figure out what was causing the hard starting, I decided to pull the engine apart again, and double-check internal engine parts. Before removing the engine from the mower, I found that the flywheel key had sheared, and the flywheel had turned about 90 degrees. Put a new key in, tried starting the engine again (I know a sheared key effects ignition timing, not valve timing/compression). After trying to crank a few times, I saw the new key was beginning to shear. After taking the engine back apart, I re-examined the camshaft. Miked the camshaft lobes - in specs. Miked the lobe on the compression release pin and just below it - pin sticks out about .015 inch. Cylinder bore looks smooth, doesn't seem to be any binding in the rotation of the crankshaft. If the compression release is not working, could that cause the flywheel key to shear, or is there another issue also? Any advice will be appreciated.

What is causing the flywheel key to shear is not properly torquing the flywheel nut/bolt or not making sure tapper of crankshaft and flywheel bore is clean and dry. There is naturally some tightness with new rings but not to the extent you indicate. Generally when a rod is thrown, there is some damage to the crankshaft. Did you reuse the crankshaft? IF so, are you sure it is clean, in spec? Do you have a Service Manual and or need detailed valve adjustment instructions?

Walt Conner
wconner5 at frontier dot com

Have you observed that you have the same TDC piston pop-up height with the "borrowed" rod etc? Is it possible you have built a hot rod high compression engine out of a sidevalve workhorse? Walt's idea of crank "truth" is good, but a little late now that the engine is assembled. Ideally you would check the crank journals with the crank set between a lathe like jig and compare micrometer readings. Finally, I am not that familiar with the L heads and realize it has a comp release, but on other engines many have relieved hard cranking with a valve adjustment. Perhaps go back over and mark exact TDC and be sure the adjustments are on the comp stroke. All comments with due respect and meant helpful.

Walt & Motoman, thank you for your replies. I did reuse the original crank. The rod journal on the crankshaft had a little aluminum build-up from the rod. I cleaned off the journal with muriatic acid, then buffed the journal so it was smooth and shiny (I learned this from another post on Lawnmower Forum, and did it once before with good results). The journal diameter was within specs per my factory service manual, and the new rod turned freely, so I thought is was okay. However, I did not check the crank for being "true" (not bent) except visual inspection. I have a friend with a lathe, and will try to check for run-out with a dial gauge with the crank in the lathe. I found a set of pdf Briggs factory service manuals online, and this is what I've been using. Single Cylinder OHV Air Cooled Engines, 2009 date. This manual gives the flywheel bolt torque as 100 lbs-ft, which is what I torqued it to. I remember reading other forums where there was disagreement over flywheel torque. I believe another member had posted a Briggs check chart that called for 60 lbs for 310000 engines. What's correct?

I remember that post of 60 inch lbs on the flywheel and it was incorrect. You have a manual and that is what you should go by. IF rod turned freely after you worked on the crankshaft I'd say there is 99% chance you are OK there. I have rebuilt many, many engines after throwing rod and never checked any crankshaft on a lathe though if you have the capability, (and I do have the capability) that certainly would relieve your mind. Did you check ring end gap when installing new ones? Most likely they are not too tight, at least .008". IF the ring set you used has a segmented oil ring, those generally put more pressure on cylinder wall but not enough to cause trouble if installed properly. I have seen posts where B&S has upped the torque to 120 inch lbs AND started using steel keys on these but I would not use steel key. I have changed to 120 inch lbs. Your key shearing problem is due to something wrong in tightening or with surfaces of crank or flywheel. There was an incident awhile back where there was a slight deformating along the crankshaft keyway which had to be cleaned up before flywheel would seat properly. The crankshaft tapper should hold the flywheel with key only being for positioning.

Walt Conner

http://faculty.missouri.edu/~schumacherl/276781SingleCylinderOHV.pdf see section 12 page 172 for specs., adjust intake .004 & exhaust .006 section 1 page 21 has procedure, since you have new internal parts. manual says .003-.005 intake & .005-.007 exhaust. flywheel nut 100 lb.-ft.

https://www.briggsandstratton.com/n...nemanuals.html?searchrequested=31G777-0290-E1

I know you have this information, just trying to help.

Try cranking the engine without the head on.
If it is hard to turn then you have a crank / cylinder problem.
The OHV cases are nowhere near as robust as the L Head engines and will warp a lot easier.
Check the bore for roundness.
If it turns over freely then you have a valve train / compression problem

The important question is why did the rod break in the first place ?
That will tell you where to start looking.

"The important question is why did the rod break in the first place ?"

Good point and we haven't heard anything about that.

Walt Conner

He mentioned removing aluminum build up from the crankshaft. Lack of oil caused that, the rod seized to the crankshaft under significant throttle and that was all she wrote.

Would be interesting to know the deck height, piston pin height, rod length differences if any of the two engines. Valves may not be opening due cam to crankshaft being out of time is probably going to come into play.

I guess you guys really mean 60 or 100 ?INCH POUNDS? My Intek 24 takes 100 FOOT POUNDS on the big flywheel nut. The taper discussion is relevant. A lot of machinery relies on proper taper for locking...such as mills , drill presses etc. If , somehow the tapers are mismatched , dirty or buggered up....problems. Just sayin'

You are absolutely right, FOOT LBS.

Walt Conner

Thanks for all the posts, sorry I haven't had time to respond. The friend I got the engine from has been a machinist, mechanic, and millwright, so he knows about engines. He's also old enough where hearing protection wasn't a big deal in his younger days. He thinks the engine seized up due to low oil. It was on a riding mower - he said that he used the mower, shut it off, then when he tried to use it the next time, the engine was seized. If it threw a rod when he was using it, he said he probably wouldn't hear it (see hearing protection earlier).

Bertsmobile1, I did pull the head off with the engine still mounted on the mower. It turner over easily with the head off.

After pulling the engine apart, here's what I noticed: Pulling the piston out, there was slight scoring the length of the cylinder wall. If you look at the cylinder with the magneto at the top, the scoring would be on each side, more pronounced on the side farthest from the camshaft. Ring end gap is 018 for middle ring; 010 for middle ring and oil ring - all within specs per factory manual. What the manual refers to as "ring land clearance" should be 002-005, but on this cylinder, it is less than 0015" for both compression rings (the thinnest feeler gauge I have wouldn't fit in the groove with the ring). I have a second piston from another engine (but same part number, same piston) where the rings are just as tight in the groove. When taking the engine apart originally, the old top ring was so tight, it would not come out in one piece, even using piston ring tool. Is it okay for the compression rings to be this tight?

"When taking the engine apart originally, the old top ring was so tight, it would not come out in one piece, even using piston ring tool. Is it okay for the compression rings to be this tight?"

No, the piston ring land is carboned up. They make a tool for cleaning them but I use a broken ring making multiple passes in both directions until the land is clean in all lands.

Walt Conner

As Walt says: clean the lands. Don't take any aluminum from the lands.

Remove the piston, remove the rings from the piston, put the rings in a padded vise, use a smooth file and file away one thousandth of material. Everything expands with heat and a mower engine is usually air / fuel cooled. This type of engine's rings expand more than a liquid cooled engine. An air / fuel cooled engine does carbon more so than fuel cooled meaning tolerance too close and you may experience ring abutment which will score the cylinder(s).

File your rings. Check them for gap tolerance inside the cylinder at the top of their travel. Use an old piston with a ring on it, turn the piston upside down to press the ring down into the cylinder until the ring on the piston hits the deck. The ring you're using will be sitting at the exact spot it will live at (TDC) Top Dead Center. This is where you want to check your ring gap. Piston isn't in your feeler gauge territory and you can see if the ring ends are straight and true.

Good luck.

Max

Walt, the teacher for the small engine classes I took also used an old ring to clean out the land. I did this, and removed the carbon build-up (a friend who's a mechanic also looked at the piston and the lands looked clean to him. He has a ring groove cleaner, but the smallest blade was too large for this piston). My question is, when you install new rings in an existing piston where the lands have been cleaned out, is it normal to have basically no land clearance, or should there be the .002-.005 clearance per the Briggs service manual?

I never check them other than make sure the rings move freely in the piston ring groove. The engines I worked on (I am mostly retired now) were bound to be out of spec somewhere but fortunately B&S engines are very forgiving. For example, I hardly ever used standard rings when doing a ring job. After inspecting and measuring the cylinder to my satisfaction, I used +.010 rings and hand fitted them to the end gap I wanted. Now I don't want to hear a bunch of - - - - about this from people here as I have been thru that multiple times over many years and I have the service experience to back up what I do. I am also equipped to and do resize the cylinder bore if I feel it is needed.

Walt Conner

As a machine shop owner, I recommend always checking ring end clearance as I described above. If there isn't enough clearance after starting the engine, the rings will grow in length and "may" experience abutment. If this takes place and tightens to the point of seizure, you'll have more problems that you do at this point. Always and I mean always check ring gap.

Always check to see if a ring compressor can collapse the ring entirely into the ring land. If the ring can't fit all the way into a new piston, either the ring land is too shallow, which very seldom is ever experienced, or the ring is the incorrect ring for the piston.

A replacement ring may have too much ring gap in mid stroke and at the bottom of the bore, however at the top dead center, it may look perfect. Check the ring gap at the bottom dead center, mid bore and top. If there the ring has cut into the cylinder, remove the material at the top of the bore until it is the same size bore diameter as the worn area of the cylinder bore. Then hone very lightly. You do NOT need a rough bore.

The reason you hone a cylinder is to hold the oil on the side of the bore for lubrication during break in.

Good luck.

mhavanti said:

As a machine shop owner, I recommend always checking ring end clearance as I described above. If there isn't enough clearance after starting the engine, the rings will grow in length and "may" experience abutment. If this takes place and tightens to the point of seizure, you'll have more problems that you do at this point. Always and I mean always check ring gap.

Always check to see if a ring compressor can collapse the ring entirely into the ring land. If the ring can't fit all the way into a new piston, either the ring land is too shallow, which very seldom is ever experienced, or the ring is the incorrect ring for the piston.

A replacement ring may have too much ring gap in mid stroke and at the bottom of the bore, however at the top dead center, it may look perfect. Check the ring gap at the bottom dead center, mid bore and top. If there the ring has cut into the cylinder, remove the material at the top of the bore until it is the same size bore diameter as the worn area of the cylinder bore. Then hone very lightly. You do NOT need a rough bore.

The reason you hone a cylinder is to hold the oil on the side of the bore for lubrication during break in.

Good luck.

Click to expand...

Well I partly agree. Actually the maximum end gap clearance will be at top of the stroke and minimum will be at the bottom. You want to be sure you have at least the min. end gap clearance at the bottom of the stroke, learned the hard way. Of course the ridge at the top of the cylinder will be smallest and should be removed first and the taper of the bore reasonably close to spec. min.

Walt Conner

Yes Sir Walt, that's what I said. lol

Except for the gap changing in the bore. If the bore is smaller at the bottom than the top, somebody going to need some training on setting up their boring bars and or honing machines. The bore should ideally be the same thru the entire length.

The ridge does need to be removed before a new ring is deployed. Otherwise, the radius made by the old ring as the cylinder wore in will not match the minute radius of the new ring. Therefore, major problems can come about and nobody going to like it. lol

Thanks for bringing to my attention I was unclear. Certainly not my intention.

Hope between Walt, Bert, Tinker, Tom and so many others we've helped this gentleman out.

All good stuff but re-reading I am not all that sure his tightness is in the bore as with out the head on the engine spins freely.
He specifically mentioned it was hard on compression and he has reasonable end gaps at the top of the bore.
Insufficient side clearence usually causes a lack of compression as the charge can not force the ring to seal against the bore.
It would have been good to see what it spun like head on & plug out .
I am leaning towards a bent cam or damage to the cam bush ( hole actually )
Possible spring bind although that should not happen at tdc as we all know.

"Use an old piston with a ring on it, turn the piston upside down to press the ring down into the cylinder until the ring on the piston hits the deck. The ring you're using will be sitting at the exact spot it will live at (TDC) Top Dead Center."

"A replacement ring may have too much ring gap in mid stroke and at the bottom of the bore, however at the top dead center, it may look perfect."

"Yes Sir Walt, that's what I said. lol"

I'm not sure what you said.

"I am not all that sure his tightness is in the bore as with out the head on the engine spins freely."

"I am leaning towards a bent cam or damage to the cam bush"

??

Walt Conner