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

   The picture is of an older 5HP Tecumseh rebuild.   It does not have the power I think it should.  It does not throw far but part of that is due to the short chute and chute angle of an old Jacobson 526 Imperial Heavy Duty Giant.   At about 1/2 of the bucket full it starts to bog down.  The governor is kicked in and working but it can't keep up and starts to die if I don't give it some clutch slip to let it catch up.  The blades are very heavy and the impeller solid.  It's only a single belt system but I think it should be doing much better.

   The rebuild seemed to go well but I could not test as there was no snow around at the time.  It start agressivly, has a crisp report and seemed to run strong.  At the time I did not have a leakdown tester but thought the rebuild went well.  It got an hour of run time, three oil changes and sold.  The buyer was not so happy with it so I returned his money.   I've run it for about an hour testing and it is a weak tosser.   I went through the carb and governor and think they are ok - that it's not a lack or gas under load or a governor problem. 

   This was one of my first rebuids and I think at that time my honing of the bore was lite - not enough.  Tonight I went to re-hone the bore and the head bolts were not very tight.  On removing the head I found some brown tackie stuff on the head gasket and head rim like in the picture.  I think possibly the headbolts were enough to allow decent but not full compression and there is leaking. 

So - a few questions:

1. Does the brown stuff in the gasket area look like the result of a leak? 

2. For honing I have a stock 3 leg hone used in a drill.  The stones are flat.  I think engines build up lip in the bore towards the top.  If that's right then the hone at the top will have one edge on lip and the other toughing down a ways in the bore missing the mid section - no scoring.   Tonight I looked at the bore with a light and it seemed fairly smooth, not glossy and sort of dull or matt.  I ran the hone in there for a while and it seemed after looking in that the top got more scroing than below so I figured it may be due to a lip.  I went in with 320 and oil by hand to hone below more and it looked better than with just the hone.  The piston is still in so tough to get the bottom section.  If the lip a problem when honing?

3. Does the brown and black areas on the piston look normal for about 3-4 hours of run time?

4. If properly honed how long should it take for the rings to seat?

5. I've never worked in a shop or took a course so judging honing is a difficult.  Any way to judge just how much is enough? 

6. I'm almost beginning to think that sticking with medium stones is better than honing with medium then finishind with fine but not positive.  Any suggestions?

7. As is, I've rehoned the bore, plan to button it up, torque the heads to spec, and run it under load for an hour to see if it improves.  Any suggestions.

8. Could the not so tight head bolts be due to normal loosening?  I torqued them on buttoning up the head but never retorqued them after that. 

Edit: I should add this engine has a 1 inch crank and heavy so I expected it to have some decent torque.

David

http://www.kedawei.com/snowblower.htm

Borat,

    I’ve had a compression gauge for quite some time but because of compression release mechanisms done count on the readings if their low.  I’ve since picked up a leakdown tester. 

   For the proper compression to expect I’m not positive after lots of reading up about compression testing.  For a new or rebuild I’d expect 130-150 if a full reading could be had but it usually can’t be because of compression release.

   The head bolts were torqued to spec and proper pattern per Tecumseh.  I did not retorque which I now think is a big mistake.  You mentioned three heatings and that’s the first guideline I’ve ever known about. 

    I’ve got Tecumseh gap specs but was not so fussy on the first rebuilds.  I’ve since picked up a digital bore gauge and some T gauges but getting accurate readings is not so easy.  I did not have those tools when I did this engine.

   It was not re-bored so standard rings and no new piston. 

    Yep, re-honing with the piston in is not the best but I’m pretty busy so a short-cut.  If this does not work out I’ll probably set the motor aside until I get more time and check it out more thoroughly.

    The valves were water tested and no leaks but I’ll be switching to testing with gas in the future.

   I generally steam clean the engine before button up.  Cleaning up the re-honing should be fairly easy.

    OK, on the likely gasket leak.  I’ll clean it up tomorrow, retorque and see what happens.

 

Friiy,

 

   The piston was pretty clean on the rebuild so the guy may have run some crummy gas in there.

    Interesting on your using medium grit.  Most of the small engine hones I’ve seen are sold with medium grit and fine special order.  I’ve got fine but thinking of not using them anymore.

    The valves as I wrote above I think are ok.  I hope to do a leakdown test tomorrow after I get the thing together and run it for a while.

    Valve adjustment seem a big of a puzzle to me because in the Tecumseh L-heads there is no adjustment other than making the valve shorter.  It seems to me that the only problem there could be would be too short an opening because of wear.  You can't increase it by adjustment other than replacing the valve. 

   I try for 30 degrees and probably come close but honing with the piston in is a big difficult – well – a kluge.

   I did not hear any chirping.  The gasket looks ok but I’ll check it better tomorrow.  If it looks crushed or out of shape I think I have a spare. 

 

   Thanks for the input I’ve got a few things to correct in my process with the biggest being retorquing after running the engine.  What was a real puzzle is just how loose they were, very easy to unscrew.  I almost think the guy may have done something but he was not a mechanical type.  Regardless they were loose and a problem.

 

David

When we rebuild the top ends of our old two strokes, we usually use three heat cycles for re-torquing purposes.  We settle on three because usually by then, no more torquing is required. 

Hey Trouts,

Are all the head bolts the same?.... sometimes there are 3 longer ones that go around the exaust valve to wick away heat....

Friiy

PS... What Borat said, I agree with also.

Borat,

    OK on the two strokes.  Screamers for sure.  It was sort of interesting years ago pulling of the quad carbs of a Honda.   I forget if the head was included but remember that there were 46 bolts to unbutton to get the job done.  The metal in the 250 Yamaha was the same as the Honda so I think all the bolts needed to button down the flimsy metal. 

    The Tecumseh head is a good chunk of metal and I've give it some cycles tomorrow and retorque.  I should have know better but got lax.

Friiy,

   This engine is slightly unusual in that all the bolts are the same length. 

    It just so happens that over the last half hour a guy who has one of my other rebuilds checked the head bolts and found them all tight.  I've got a 10hp rebuild here I've used for the last three storms and is very powerful.  The leakdown on that one is 5% but tomorrow I'll check the headbolts. 

Ke  

Quote:  The metal in the 250 Yamaha was the same as the Honda so I think all the bolts needed to button down the flimsy metal. 

Don't know what you mean by "flimsy metal".  The Honda 750 engine is one of the very best motorcycle engines ever made.   The Yamaha two strokes are also famous for their durability and could take punishment better than anything. The RDs that I'm working on have only four sleeve bolts per head. 

 How many two cycle engines are you aware of that can be over-bored eight times?   How many engines do you know of that can be spun 4000 rpm past their red line, have horsepower increased by nearly 100%, raced all day and not blow up?  The fact that these engines are still around, running very strongly at 35 to 40 years old is a tribute to their durability.     These, as well as most Japanese are far from flimsy.         

   The early 250’s could only be bored out twice – at least for max speed racing.  I’ll stick with the crummy metal though which says nothing about the total design quality especially of the 650 and 750 quad carb 80’s machines.

 

   The Jacobson 5hp is much better.  The bore was re-honed.  The exhaust valve lash found way under and the intake .003 under.  With that and the loose head bolts it looks like I was paying too much attention to TV during the rebuild. 

   The machine is tossing very well and not bogging down like before – a big difference. 

 

   Unfortunately what I found is the throw distance was not like other machines.  It turns out the Jacobson has a fairly large crook in the back of the chute.  It was designed that way so does not throw high.  Also, the top hood does not open fully to allow the main chute to throw clear of the hood.  The hood always lowers the angle from the main chute.  With the hood cut back and inch the thing will probably gain 5 to 7 feet in distance.  As is the machine is throwing like it did when it came out of the showroom.  The through put is ok but it’s not a distance machine. 

    Unlike modern machines and even newer Jacobsons this early one had a great heavy bucket and good blades.  Today I ran it parallel to the sidewalk buildup which had a lot of iced up solid snow as it’s been plowed over a number of times and sitting for a week.  The 526 did very well cutting through the crud probably doing what newer snowblowers could not.