The Jack's Small Engines Forum - Join Our Online Community
Reply to post

Hot!21HP single cylinder 331777 internal damage

Author
4cycle
Starting Member
  • Total Posts : 13
  • Scores: 0
  • Reward points: 0
  • Joined: 2017/11/27 10:09:31
  • Status: offline
2018/07/02 21:17:08 (permalink)
0

21HP single cylinder 331777 internal damage

I have acquired two 21HP B&S 331777 engines with internal damage.One had the decompression lever come off cam and was pushed out side of case behind starter,the other had the counterweight come off crank from broken counterweight links.I am starting to put the one with the broken links back together after parts arriving.I noticed when taking it apart,bottom of case had broken pieces of the old links and I think the cause was top crank bushing was worn.I could move the crank side to side when holding engine case.I have installed new top bushing and seal and now have no noticeable slop of crank.I wonder how top bushing was worn.Must not have been getting oil?
I will have about $250 (hopefully) into these engines total,so I will be lucky to make $10 an hour if I sell both for $500 when fixed.Or I can look for a Craftsman lawn tractor that needs a motor,seems like many of them use this engine.
Just seeing if anyone has any tips to help get these put back together and running.

12 Replies Related Threads

    4cycle
    Starting Member
    • Total Posts : 13
    • Scores: 0
    • Reward points: 0
    • Joined: 2017/11/27 10:09:31
    • Status: offline
    Re: 21HP single cylinder 331777 internal damage 2018/07/03 23:42:27 (permalink)
    0
    I started assembly of the engine that had the broken counterweight links.I installed the crank and flywheel in the upper casing half,torqued the connecting rod screws,installed the cam.That part went well,when I tried to install the lower case half (sump),I could not get the two halves to come together all the way.Even after removing the oil pump rod and governor assemble I still had about a 2 mm gap between the two,good thing I did not have the gasket installed,ready to make it oil tight.
    After trying it a few more times I think I found the problem.The only thing stopping the two halves from coming together is the counterweight.It has a groove that the bottom case fits into,flush with the top of the bottom case,same as the rest of it that seals the two halves.
    After using a micrometer I found the slot in the counterweight at .245in and the part of the bottom case that it fits into it at .250,so the two pieces will not quite fit into one another.That is why the top and bottom cases will not come together all the way.It also would explain that if you forced the two halves together with the case bolts,it would put force on the crank on one side from the counterweight links,causing the top case bushing to wear out and eventually break the counterweight links.Just like when I first tore the engine down.
    I checked my other engine and the bottom case is also at .250 where the counterweight is to fit.It would be a job for a machinist to machine it down to .245 or less,the counterweight is cast iron and even harder to machine.
    AVB
    Super Member
    • Total Posts : 703
    • Scores: 31
    • Reward points: 0
    • Joined: 2017/06/21 16:35:48
    • Location: Elora, TN
    • Status: offline
    Re: 21HP single cylinder 331777 internal damage 2018/07/04 14:48:56 (permalink)
    0
    I know this might sound like dumb question and it is because I can't the counter weight I got put up. But is it possible that you have the weight upside down?
    4cycle
    Starting Member
    • Total Posts : 13
    • Scores: 0
    • Reward points: 0
    • Joined: 2017/11/27 10:09:31
    • Status: offline
    Re: 21HP single cylinder 331777 internal damage 2018/07/04 15:25:42 (permalink)
    0
    Thanks for the post AVB,that is a good question,I do not think so though,I have the crank from the other engine all intact to go by.

    Attached Image(s)

    AVB
    Super Member
    • Total Posts : 703
    • Scores: 31
    • Reward points: 0
    • Joined: 2017/06/21 16:35:48
    • Location: Elora, TN
    • Status: offline
    Re: 21HP single cylinder 331777 internal damage 2018/07/04 17:33:08 (permalink)
    0
    Never mind I found an image of the counter weight not possible to install upside down.
     
    I don't see how it ever worked if there is .005 too tight of fit as it had to pressed in place which have locked up the engine.
     
    Now it easier to machine the counter weight than the sump though a good machinist with the right cutters can do either one.
    4cycle
    Starting Member
    • Total Posts : 13
    • Scores: 0
    • Reward points: 0
    • Joined: 2017/11/27 10:09:31
    • Status: offline
    Re: 21HP single cylinder 331777 internal damage 2018/07/04 18:56:22 (permalink)
    0
    Thanks,AVB,good thing a machinist will not be necessary,I am lucky there is an engine machinist in my area,finding one without an attitude is usually the hard part,(BTW my dad was a machinist).
    After watching more than one Youtube videos where they were able to get the cases to close up no problem,I decided to take another look.With better light during the day I found I could get the case to close up if the counterweight was all the way to the bottom of the case.I seen the counter weight needs a slot because it moves opposite the piston.
    I got the case closed and turned the flywheel,the case separated again when the weight moved up toward top of engine.Removed bottom sump again and could see were the cast weight left marks in the aluminum sump.Found that the sump was bent were the weight connects with it.I did not see any old wear marks so I do not think this engine did not have this problem when new.The counterweight only rides on the sump about a 1/2" depth of it's groove.
    I was able to hit the sump with a soft faced hammer to straighten were the weight rides.Now I can get the cases closed,turn the flywheel by hand,and the cases do not open up.I should be ready to install new gasket and sump bolts,after installing governor assembly and oil pump rod.
    I did see on Youtube that taking off the oil pump cover and removing oil pump would be an easier way to go than trying to get the oil pump rod to line up with the slot on the cam when putting the sump back on.
    AVB
    Super Member
    • Total Posts : 703
    • Scores: 31
    • Reward points: 0
    • Joined: 2017/06/21 16:35:48
    • Location: Elora, TN
    • Status: offline
    Re: 21HP single cylinder 331777 internal damage 2018/07/05 07:31:32 (permalink)
    0
    Hmmm, I wonder how the sump got bent. Now have seen on one engine where the counter weight busted the crankcase from striking it after the connecting link broke.
     
    As for the bent sump that is very unusual as most of these engines are on riders and are fairly protected from direct strikes.
     
    So far I haven't any problems getting the oil pump drive rod aligned. I just turn the crankshaft after get cover mostly on and the two points align and the cover drops into place. I do see where it is easier to see the alignment with the Gerotor cover off
    4cycle
    Starting Member
    • Total Posts : 13
    • Scores: 0
    • Reward points: 0
    • Joined: 2017/11/27 10:09:31
    • Status: offline
    Re: 21HP single cylinder 331777 internal damage 2018/07/10 09:08:18 (permalink)
    0
    Good tip for aligning the pump drive rod AVB,sometimes it will drop out of the sump when fitting it over crank when dropping in place onto crankcase.I got lucky with mine after prepping case for new gasket and dropping the sump onto crankcase,it lined up and did not fall into crankcase.
    After sump and case were together I turned crank and everything turned easy and felt smooth,I used assembly lube on crank and cam.The next day I mounted it on a Lawn tractor,put oil in it,turned it over without starting to get the oil pump primed.Then went to start it and it stared instantly,a good sign!It runs great,everything sounded really good,I installed new top and bottom oil seals when I had it apart,so now it should be a good engine until the decompression lever falls off cam.I found many video's of that situation on Youtube.
    That is the problem with the next one I have to put back together.
    4cycle
    Starting Member
    • Total Posts : 13
    • Scores: 0
    • Reward points: 0
    • Joined: 2017/11/27 10:09:31
    • Status: offline
    Re: 21HP single cylinder 331777 internal damage 2018/07/16 11:17:38 (permalink)
    0
    The parts arrived for the other motor that had the decompression lever fall off the cam and go thru side of case.I had a local welder TIG weld the hole in case,I found a video of how to do it on Youtube.You have to put it in a gas BBQ on high to get it up to temp when trying to use alumiweld,but it can be done.
    The replacement cam went in no problem after torquing the piston rod bolts.The sump went on with no problems after turning motor over by hand to get the oil pump rod to line up.There were a couple problems after that.
    I adjusted valve clearance at the rocker arms,.003-.005 at top dead center,I did this with the sump off so I could see the cam lobe location.When I adjusted them,the lobes were at the all the way closed position,there was clearance at the rocker arm and valve stem.
    When trying to start engine for the first time it did not want to start,ran really rough and could see fuel vapor coming out of intake.I figured the valves were not closing enough.I checked procedure for adjusting valve clearance on these motors,manuals say rotate engine 1/4 turn past TDC.Another said check TDC by inserting tool into cylinder at spark plug hole,rotate cylinder past TDC to point were piston drops 1/4" inch.The Youtube videos of adjusting valves on these is a joke,they just kind of wing it.
    I used the piston 1/4" down from TDC method,they are both close to the same cam positon.After re-adjusting valves the motor started instantly and seemed to run normal,accept for surging really bad at anything but wide open throttle.So I am thinking I did have .003" valve clearance at the very bottom of the cam lobe,but that is not how B&S wants you to adjust them.They want the cam to be at somewhat at the ramp up position of opening the valve,anyway it works.
    The surging problem turned out to be a problem with the carburetor.There is one good video on Youtube that shows motor like mine surging the same way before cleaning carb,and running smooth after.Mine has the Nikki carb and the problem was in the intermediate jet,it would smooth out if you partially choked it.I had to take the carb apart,it did not look like it needed cleaning so the problem could have been leaking welch plug or fuel stem o-ring or noodle gasket was not in position.
    After putting carb back on,motor is running smooth,I did have to adjust mixture screw to get the surging out of low throttle.
     
    Roy
    Moderator
    • Total Posts : 528
    • Scores: 13
    • Reward points: 1
    • Joined: 2016/07/27 22:51:23
    • Location: British Columbia
    • Status: offline
    Re: 21HP single cylinder 331777 internal damage 2018/07/16 11:39:45 (permalink)
    0
    Good that you got it running satisfactorily. You say you adjusted the valves with the sump off. You probably found the clearance disappeared when the engine was reassembled and the cam was supported in the proper position.
    AVB
    Super Member
    • Total Posts : 703
    • Scores: 31
    • Reward points: 0
    • Joined: 2017/06/21 16:35:48
    • Location: Elora, TN
    • Status: offline
    Re: 21HP single cylinder 331777 internal damage 2018/07/16 12:15:03 (permalink)
    0
    As Roy said you must have the engine assemblrd as the camshaft must be supported on both ends or your adjustments are no good.
     
    The reason for the 1/4" pass TDC compression stroke is because the ACR (Automatic Compression Release) interference at TDC. Doing it this way allows you to adjust valves at the same time. An alternate method to rotate the crankshaft until one of valve fully opens and adjust the opposite valve. Then rotate until the adjusted valve is fully open and adjust the opposite valve. Takes longer but achieves the same results. This way there is no ACR interference.
    4cycle
    Starting Member
    • Total Posts : 13
    • Scores: 0
    • Reward points: 0
    • Joined: 2017/11/27 10:09:31
    • Status: offline
    Re: 21HP single cylinder 331777 internal damage 2018/07/24 10:57:17 (permalink)
    0
    Thanks for your reply's about the valve lash adjustment.That makes sense that my adjustment was not accurate with the sump cover off not supporting the cam.Also I could see rotating crankshaft 1/4 past TDC to not be adjusting valve lash while touching the decompression lever.The manual that said adjust valve lash with piston 1/4" down from TDC could have been for engines without decompression lever on cam.
    AVB
    Super Member
    • Total Posts : 703
    • Scores: 31
    • Reward points: 0
    • Joined: 2017/06/21 16:35:48
    • Location: Elora, TN
    • Status: offline
    Re: 21HP single cylinder 331777 internal damage 2018/07/24 11:34:02 (permalink)
    0
    Actually it is for all ACRs, ramped and bump styles as valve lifter can still be sitting on the decompression area of the camshaft lobe. Many older L-heads actually had a permanent bump or ramp ground on the camshaft lobe so there was always a small amount of decompression even at full throttle.
     
    With conversion to swing arm ACR this went away and increased fuel economy and hp/torque. This one reason the increase power specs even the same CC engines. There are also other improvements affected the new engines ratings.
    Jump to:
    Copyright © 1994 - 2016 Jacks Small Engine & Generator Service, LLC