Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

I have here a piston connecting rod that has just a little too much play in the bearing/bushing that connects it to the shaft.  Is there a bearing/bushing that can be replaced or does the whole connecting rod/shaft assembly need to be replaced? This is off of a Honda 5hp horizontal shaft 4 stroke engine that belongs in a honda single stage snowblower (HS520). 

Have you put in new bearings?  Or is the slackness happening with the old bearings?  Chances are that if you put in a new set of plain bearings, it should be within tolerance. 

I have not loosened the bolts that hold the rod to the shaft (no new bearings or other parts).  Are there bearings inside of there?  Or does the piston's connecting rod just rotate on the bare metal of the shaft?  If a bearing existed I thought that I would have seen it in the "exploded view" of the part.  How would a new one get installed?  Do they clip on?

The drawing looks similar to Tecumseh snowblower engines - no bushings or bearings.

Aluminum rod, the two pieces bolted together, rides on the crankshaft journal without other parts, aluminum riding on steel. Wear is pretty easy to see. The crankshaft journal will have a thickness spec and the rod diameter will have a spec. Tecumseh provides these online. I think all Honda manuals are pay-for, not online.

I'm not certain if there are plain bearings in that particular engine nor if the small Honda engines use replaceable bearings in the connecting rod big ends.   I know that larger engines have babbitt type flat or plain bearings that can be popped out and replaced. Usually on one end their is small indentation to put a tool in to pry the old bearing out.  Some flat bearings are also removed by tapping the edge of the old bearing to cause it to rotate out of the semi circle of the the bearing seat.  Take the connecting rod bolts out and have a close look to see if there is a very fine cross section line between the outer surface of the bearing and the inner area.  If so, you might be in luck and just need a bearing change. 

Regarding the parts diagram, you're right.  Don't see a bearing there.  I'd look into it nonetheless.

trouts2 wrote:

Yes, honda manuals are "pay for"  so I don't have a thickness spec to go by.  Since the connecting rod is aluminum and the crank shaft is steel, is it fair to say that any wear would occur on the connecting rod (softer metal) and not the steel (hard) crank shaft?.  That being the case, would a new connecting rod solve the problem of too much slop in the fit?  This snowblower is only a few years old and was used on a 15 foot driveway as a "backup" to a larger 8hp 2 stage blower. It's just out of warrantee and the rest of it looks like its been sitting in a showroom (mint). That said, there's no reason to beat a dead horse.  I'll loosen the bolts holding the connecting rod and see what I find .

I found a good write-up on this subject online in a book entiltled "Repairing Your Outdoor Power Equipment" by Jay Webster:

http://books.google.com/books?id=-bEBXd7oUokC&pg=PA35&lpg=PA35&dq=honda+crankshaft+journal&source=web&ots=dj69iuA2Tl&sig=JR3tS3r-CSN5LiKTuzrCN5eMB7A&hl=en&sa=X&oi=book_result&resnum=8&ct=result#PPA36,M1

Don't you hate it when someone only gives you part of the story. So here goes: A small plastic cam pulley in the top of the engine broke.  The engine was serviced by a Honda tech and the plastic cam pulley and small timing belt replaced. When the repaired engine was started you could hear a knocking noise (the motor ran and the knock was most noticable during idle).  The tech made a call to the owner and said "looks like you're also going to need a new piston, connecting rod, and crankshaft."   The cost of all this new extra work (just out of warrantee) was enough for the owner to decide to just throw in the towel.  He decided to cut his losses.  He paid for the work that was done and brought the snowblower home unassembled in 5 boxes.  

Does everything about this story sound right? Tonight while I was looking at the engine I noticed a few things. First, when the engine was re-assembled gaskets were not used. Instead the tech used goopey stuff. And  the piston has indents on top from the valves.  I have sometimes heard that the gaskets act as spacers and dismissing them from the assembly can cause the valves to tap the piston. I don't know enough about honda engines to say that a gasket  should be considered a neccessity on a  small 4 stroke ohv .  But look carefully at the piston in the photo. You can see indentations if you look really hard (sorry for the bad photo).  Are these indentations supposed to be there? Maybe that's the way honda makes pistons on these small engines. Or maybe the broken plastic  timing wheel  caused the valves to slam into the piston.  Either way, now there's just a little too much play between the connecting rod and the crankshaft journal. 

What to do?  Are gaskets the way to go?  Will a new connecting rod be enough to solve the problem?  Does the piston need replaced?  Is this becoming a tangled mess?  no end in sight? Originally I assumed  that the honda tech knew what he was doing  (or at least more than me), so my plan was to follow the tech's  lead and pick up where he left off.  But those valve impressions in the piston have left doubt in my mind. Ussually my advice to others would be to trust your initial instinct.  So I guess I'll go with that for now and  assume that the piston is supposed to have indentations and the tech knew what he was doing. 

Any assistance at this juncture would be appreciated.  Has anyone left out gaskets (and used goopey stuff instead) when assembling honda ohv 4-stroke engines? Will a new connecting rod   (part # 13200-ZL8-000 $39.36) solve the problem with the worn bearing surface?

 

Did this engine knock before the mechanic worked on it ?  I doubt that replacing a timing belt
would result in knocking of any sort.

The depressions in the piston top is normal.  They allow the piston to move further upward without
hitting the valves.  You'd clearly see damage to the piston if the valves were hitting it.

Are you sure there is too much play between rod and crankshaft ?  What about the bearings on the
ends of the crankshaft ? There does seem to be a bit of wear there, how old is this engine ?  Are
the bearings loose internally or is it between the bearing and crankshaft ?

Sometimes knocking is from the piston being too loose (like Subaru's famous piston slap).  This
will show up as scuffing on the piston skirt.

I'd be a bit surprised if you needed a new crankshaft unless the ends are too worn.  It is certainly
the most expensive part in all this.  Replacing the rod, the crank end bearings, and probably the
piston and rings for good  measure, might be all you need and shouldn't be that expensive
(you'd want to rebore but you probably can't on a small engine like this).

Given Honda's prices for parts it may be cheaper to buy an new engine.  What's the condition of the
rest of the machine ?

Paul

pvrp wrote:

Thanks for clarifying the depressions on the piston.  There's no damage to the valves. I looked at the bearings on the end of the crankshaft and they seem perfect in every way. I have not removed the connecting rod from the crankshaft yet.  (is there a replaceable bearing there or does the connecting rod just spin directly on the crankshaft?)

The honda HS520AS was purchased new in 2005.  It was a second "lighter" snowblower for a 10-15 foot driveway in New England.  The owner purchased an extended warrantee and had it serviced every year.  There is almost no wear on the paddle set and the rest of the blower is mint. That's why I didn't want to toss it in the trash.   With electric start  I thought it would make a nice blower for my dad.  

I'm not sure how I would assess a "loose piston." The piston is certainly loose as it flops from side to side but I'm not sure what to guage it on. Same goes for the connecting rod I suppose.  How much is too much?  

As mentioned, the indents on the piston crown are normal.  Whether the piston is good or not is a different story.  If there are no obvious signs of excessive blow-by, it and the rings are probably good. 

What tests did you do to check for play between the crank and the con-rod end?  There should be absolutely no detectable lateral play there whatsoever.  Also, check the crank end play in the bearings.  It also should have no detectable lateral play.   The cases in these engines don't usually have gaskets.  They are metal to metal surfaces and must have a coating of bonding material in between them.  I usually use Yamabond.   All the major Japanese engine manufacturers have their own bonds.  Buy whatever is least expensive. 

Also as suggested, before you start to hemorrhage money on that engine, check the price of a  new replacement.  Check out Small Engine Warehouse.  They have a good selection at very good prices.   Heres a link:

http://www.smallenginewarehouse.com/default.asp  

So the engine is not very old at all.  Why would the timing wheel (whatever that is) break
in so young an engine ?

Personally, I would not go about rebuilding an engine without the service manual from
the manufacturer.  It will tell you (or should anyway) what the various clearances are so
you can tell if there's too much or not.  The manual can also be helpful when you
reassemble things like the timing belt (or chain or whatever) since you want the
valves to open and close at the right moments.  There are usually marks on the parts
to help you align things properly.  Also you'd want to adjust the valves and you need the
clearance values for this.

The piston clearance is measured by inserting a feeler gauge between the piston and
the cylinder wall, without the rings.  There has to be some clearance as the aluminum
expands when heated. Someone around here may be able to say what a normal amount
would be.  My days as a mechanic were decades ago and I can't remember off the top of
my head.  You can probably find the value somewhere on the Internet.

Connecting rod big end bearing clearances can be measured with a sort of putty that
you insert while reassembling things then measuring the thickness of the putty (if
I remember correctly, I've never done it myself).

From the drawing it doesn't look like there are any bearings.  Why don't you remove
the connecting rod so you can see what's going on down there ?  You'll be able
to see some signs of wear if there is any.  Again having the manual would be nice
to know what to torque those bolts to when you reassemble.  They're not something
you want to come undone with the engine running.

It would be nice to know what the condition of the engine was before the mechanic
worked on it.  What happened to break the timing wheel ?

Oh, and using a sealer instead of a gasket is common, but I wouldn't replace a
gasket with it if there was one originally.  The mating surfaces have to be perfect
for the sealer to work properly so you have to be really careful when you're cleaning
the surfaces not to scratch them.

I have trouble accepting that this engine knocked beforehand unless it ran out of
oil at some point.  Or the oil was never changed, and even then it's not really old
enough for that.

Paul

P.S.  Is it my imagination or are there nicks to the little teeth of the bigger gear on
the end crankshaft ?