trouts2

Followup on the rebuilds.

   The 5hp with the cracked block is finished and running very well.  Currently there is PC-7 in the cracked area with about 20 minutes of run time with the glue holding under heat so far so good on that part.  The motor is running very smoothly.  This motor had broken governor which I missed during the initial buttoning up.  The rod or a piece of the rod hit the flyweight and teeth on the governor assemble breaking the plastic governor gear.  There were long delays getting the assembly off it's post and getting a new one.   So the 5hp is running very well and the glue holding so far.  If it fails I'll take it apart again, clean everything and re-glue with I think it's JB-Weld.  The big deal for me is the rebuild part went very well.

  During the delay a 7hp Toro that was pushing oil was rebuilt and that one went very well.  It got rings and a valve job.  All the internal tolerances were to spec with the Tecumseh L-Head manual except the cylinder bore which I can't measure. 

   Also finished after delays was a Tecumseh 8hp which got rings, rod and a valve job.  The governor arm was not moving and controlling high speed so I took it apart and inspected everything.   Everything was ok in there and on putting it back together the governor responded properly so a mystery.  I don’t see how that was possible because there’s no room in there for the governor gear to be anyplace but in it’s proper place and weight able to move.  ??  Anyway I put the cover back with just a slit of an open space and a flashlight shining in to verify the govern gear meshed properly and then buttoned it up. 

   This all has been a great experience for me and very enjoyable.  I’ve had a lot of questions on this thread and a couple of others with related questions and appreciate the all the helpful advice.  When I started out I never had a concept of rings (plural) and the function of the distinct ring types.  By the way, Friiy, I never got a paper with the ring sets until the third set of rings cam in which explained the ring types and groves which by that time I was aware of.  If that paper came with the first set it would have solved a lot of questions I had. 

   The rebuilding was enjoyable, done in the cellar on my spare time watching TV and will give a few snowblowers an extension on life.  I’ve got two more motors with problems and will be doing those in the cellar during the Olympics.   As a note Harbor Freight opened an outlet close by and offering a 6.5 hp OHV engine with a cast iron bore for $129.  These motors have fantastic reports  on the net and an alternative to rebuilding. 

Thanks for the help:

Trouts2

You can get the manuals here:

http://apache.ariens.com/cgibin/ctrg0005?SESSIONID=28702a3ad72bf4c0aa733c4cb825206b&site=arienss

   The 924001 is a 724 and a very nice snowblower.  The dash controls on those have all the refinements of earlier models

and great.  It's one of the better older Ariens classics.

   If the 9xxx number you gave was from the tag on the machine where the model number was then it's a 1977.

Niper99

   If you were reviewing the job done by someone in your shop then you’d probably be right.  You could count on the guy that did the lapping to have done the job right.  I think I did not do the lapping right.

    The valve face was grayish.  It seemed smooth and even and the seats similar.  I figured since I still had a leak I might not have done the lapping well enough.  I tested them with water in the ports and there was water at the valves.   So poor lapping job.

    There was enough margin and lash to do them again so I did and decided to stay at it for a while and do a better finish also.  I’m using Permatex which is a course and fine together mix.  When you grind the compound breaks down to a fine grit and you finish with the finer broken down particles. 

   I ground quite a bit and got the same gray even looking finish.  I then did not add more compound but let it break down and ground with that for a long time. After a while the face top and bottom part started to get polished and reflective.  The middle of the face was gray still.  That told me the face was somewhat concave and the seat somewhat convex.  I ground more but slowly and evenly and eventually the whole face got ground and I think flatter and smoother than previously.  The full face ended up shiny and smooth. 

   I checked the job with water in the ports and no water leaked out of the valves.  So I think the lapping was ok this time.   I put the thing back together and it would not start.  Gas and spark were fine.  I took off the carb and muffler and put air in through the plug again with the cylinder at TDC (and a board to hold it there).  There was a lot of air coming out of the breather port.  I drained the oil and there was a lot of air coming from the oil check hole.  There was no air felt on my thumbs at the intake and exhaust ports now.  I think the valves are ok but I have a ring problem.  It was there all the time.  I think the motor had both a ring and valve problem. 

    I’m seat of the pants guessing at the air flow through past the rings because I don’t have a proper leak down tester.  At 50psi in it seems like a bunch leaking through the rings.  When I block the oil input there’s a lot of air blowing out the breather. 

   I ordered rings this morning, they’ll be sent out Monday and few days later installed and I’ll see what happens.  I’m still fairly new at engine internals so I’m pretty sure got the diagnosis wrong and the lapping wrong.  Hopefully I’m no the right track.

   Since I'm confused about what's going on with the weak compressions and my thinking it's due to a compression problem I came up with a test which I think is valid.  I hooked up an air compressor through an adaptor to the spark plug hole.  I got the engine at TDC on the start of the power stroke.  Both valves should be fully closed.   40-50 psi of air was pumped in and there was leaking from the carb muffler area.  After taking off the carb and muffler, air was coming from the exhaust port.  On trying to block it off with my thumb there was significant pressure against my thumb. 

   After thinking about how that's possible I thought possibly the tappet might be lifting the valve.  There was 8 thousands clearance which is the max so ok.  There must be a poor seating between the valve face and seat.  I lapped the valves but did not pre-grind them.  I don't have the tools for that.  I figured a good lapping would be enough.  On inspecting the face and seat they looked ok with a magnifying glass.  ?? I guess not.  I think I've found the problem but if anyone has any comments about the test please let me know. 

  Will re-lapping be enough?

trouts

    1. New points and condenser and getting a nice spark with the spark tester.  When I test with the plug to ground it gets a nice spark.

    2. Removed the head and lapped the valves.

    3. Put the head on a plate that .0005 flat over 17 inches and notices a slight irregularity in the head.  I could not measure it but possibly it might have been up to .003 diagonally across the head.  I ground it on the plate with 600 wet and removed the wabble. 

    4. Put on a new head gasket, Tecumseh not aftermarket.

    5. Torqued the head to spec and to the Tecumseh pattern.

    6. Rebuilt the carb just in case and installed a new gas line and filter.  I normally put in gas through the plug bit as it's been mentioned above I just wanted to eliminate as much as possible. 

    7.  The timing was reset with 20 point gap and the opening of the points happeneing as close to TDC as the points case allows for with rotation.  I don't think it's mechanically possible to get it closer to TDC than how it's currently set without changing the gap to a smaller gap.

   8.  The compression has stayed the same 60 and a poor 60 at that.  Real good engines I've tested go to 60 on the first pull and 90 on the second.  This engine goes to 30, 45, then 60 on three pulls.  Since I can't run the engine that's a cold reading.  The cold wet is 80 which made me suspect valves.

   9. There is no compression release of any type that I can see by watching the valves with the head off and turning the crank by hand.  There is no MCR in the drawings.  There is no valve movement other than expected with the 4 strokes.

  10.  On trying to start the engine it is a bit worse than before.  It's sometimes gets a few very faint fires.  The plug ends up wet all the time if it I keep cranking.  If I just have gas going through the plug for better control adding small amounts it will just barely fire once or twice.  If I keep pulling and testing the plug eventually gets wet.  I"ve done this a bunch of times with 4 new plugs. 

   11.  I"ve got gas and spark.  The valves have been lapped and look good along with the seats.  I"ve got a high power magnifier eye piece and the seats and faces look ok so I think from a compression standpoint the valves are not the problem.

   12.  The valves are not the problem.  The head and gasket are I think ok.  There was an issue with the spark pulg hold but it's been helicoiled and tested with talcum power around the base and seems fine. 

   13. It rained and a wind blew off the tarp covering the head.  The piston was down an inch into the cylinder so water gathered in the top inch and stayed there.  I drained the oil thinking there would be water but no water leaked down past the rings into the crank case.  I removed the oil to check.  It seems odd as there are ring gaps and I would have expected water to run through - but no water in the oil. ??

  14.  All the above seem to make me think the cylinder wall is cracked or the rings are bad.  Given that the engine ran fine not so long ago I don't think it's the rings or a crack.  ???  What have I missed??