Intek engine hard to turn over after new rings

[Captn Cliffy]

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.

 

[Tinkerer200]

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

 

[motoman]

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.

 

[Captn Cliffy]

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?

 

[Tinkerer200]

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

 

[mechanic mark]

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.

 

[bertsmobile1]

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.

 

[Tinkerer200]

"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

 

[mhavanti]

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.

 

[motoman]

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'