Hello,
Have been doing alot of research on this topic.
From what I have gathered, the bores were not coated. The piston was, with a layer of hard chrome. Still trying to understand what rings were used. I am sure I'll get more detail when I drop off the parts next week.
This guy seems to know his stuff. And was highly recommended by a local performance shop. Will update when I drop the stuff off.
Regards
Have been doing alot of research on this topic.
From what I have gathered, the bores were not coated. The piston was, with a layer of hard chrome. Still trying to understand what rings were used. I am sure I'll get more detail when I drop off the parts next week.
This guy seems to know his stuff. And was highly recommended by a local performance shop. Will update when I drop the stuff off.
Regards
Here's the deal on the HS40. Standard bore is 2.6250. Std piston measures 2.6215 for .0035 piston to wall clearance. Tecumseh specs are .004-.0058 on a inspection. Of all of these that I have torn down they are either so close to the .0058 which might as well just be .006" which is what I go by, that they don't need resized and you can just use a 2 5/8" flex-hone with either trans fluid or honing oil and like 6 up/down strokes MAX.
IF the cylinder actually is like .008 big/tapered/scratched/whatever a +.010 piston WON'T fix it-you just can't get the issues fixed with that little material to work with. So the 35546 +.020 piston is what I always wind up with if you have to resize.
Tecumseh says to use a rigid hone (Like my Sunnen AN-112) to resize and 390 grit stones. Well 400's are what's available and they must be silicon carbide. The ONLY lubricant I have had sucess with other than what I use (Goodson Honing Oil) is automatic trans fluid.
Anyway here is where I see BORING your aluminum cylinder +.020" over maybe not a good idea. IF say the hole is just .008 big where the rings ride which is only where it is going to be worn than you have .012 to mess with which is .006 on any two sides. That is less than the thickness of a business card. AND you still need a honed cross hatch finish. In the end all that is going to matter is that the cylinder is ROUND and NOT tapered and has a good finish to hold oil and help seat the rings. PERIOD. ANY minute angle to not being exactly at 90 degrees to the crankshaft isn't ever going to be noticed and besides if it's that bad there just isn't enough material there to correct for some super oddity like that. I have went so far as to take a H30 and hone it .125" to take a HS40 piston with zero problems.
Also since I have gone this far other issues you are going to incounter is the cutting of the seats. I guarantee if this engine has any amount of run time on it that the exhaust guide is going to loose and will require reaming and using a OS stem exhaust valve. The seat needs to be cut at a 90 to the guide and if the guide is worn-which it is-than the seats will suck.
Setting the valve lash is a whole nother fiascio. The tappets are going to be worn on the valve stem end and will have like a crater pounder into them because the stems are smaller than the OD of the tappet. You need to grind the "ridge" off the tappets to get a flat surface restored to them or just replace them with new. Also the cam is going to have worn the bearing journals or saddles on the bottom so that is going to have to be compensated for. Basically all of this equals areas that all need to be addressed. The cam must be in it's normal operating position to accurately set the valve lash as well as the valve springs installed. How any shop can claim to do this without basically reassembling the engine is beyond my grasp.
BTW the cylinders are plain aluminum and the piston is TIN coated.
IF the cylinder actually is like .008 big/tapered/scratched/whatever a +.010 piston WON'T fix it-you just can't get the issues fixed with that little material to work with. So the 35546 +.020 piston is what I always wind up with if you have to resize.
Tecumseh says to use a rigid hone (Like my Sunnen AN-112) to resize and 390 grit stones. Well 400's are what's available and they must be silicon carbide. The ONLY lubricant I have had sucess with other than what I use (Goodson Honing Oil) is automatic trans fluid.
Anyway here is where I see BORING your aluminum cylinder +.020" over maybe not a good idea. IF say the hole is just .008 big where the rings ride which is only where it is going to be worn than you have .012 to mess with which is .006 on any two sides. That is less than the thickness of a business card. AND you still need a honed cross hatch finish. In the end all that is going to matter is that the cylinder is ROUND and NOT tapered and has a good finish to hold oil and help seat the rings. PERIOD. ANY minute angle to not being exactly at 90 degrees to the crankshaft isn't ever going to be noticed and besides if it's that bad there just isn't enough material there to correct for some super oddity like that. I have went so far as to take a H30 and hone it .125" to take a HS40 piston with zero problems.
Also since I have gone this far other issues you are going to incounter is the cutting of the seats. I guarantee if this engine has any amount of run time on it that the exhaust guide is going to loose and will require reaming and using a OS stem exhaust valve. The seat needs to be cut at a 90 to the guide and if the guide is worn-which it is-than the seats will suck.
Setting the valve lash is a whole nother fiascio. The tappets are going to be worn on the valve stem end and will have like a crater pounder into them because the stems are smaller than the OD of the tappet. You need to grind the "ridge" off the tappets to get a flat surface restored to them or just replace them with new. Also the cam is going to have worn the bearing journals or saddles on the bottom so that is going to have to be compensated for. Basically all of this equals areas that all need to be addressed. The cam must be in it's normal operating position to accurately set the valve lash as well as the valve springs installed. How any shop can claim to do this without basically reassembling the engine is beyond my grasp.
BTW the cylinders are plain aluminum and the piston is TIN coated.
Thanks for the detailed response. I will be provding the 35546 OS piston/ring set. NOS stock crank etc. Once I visit this guy I'll have a pretty good idea of the quality of work I will get. I am micing off and pin gaging the valves/guide clearence. If I need to get OS valves I have found them. They are on hold for me. One thing I am 99% sure of is that the pistons are not tin coated, rather hard chromed. I have access to this process and am told by them that the NOS piston I provided for review indeed is chromed. That's what they told me. Tin is soft. Not sure of its lubrication properties.I cannot see where this would be used in this type application. Hard chrome make more sense for wear resistence. I guess we will see.
Thanks again,
Joe
Thanks again,
Joe
The reason for my detailed response is that there is a LOT of misconception about any aluminum cylinder/aluminum piston engine-in all applications. I have been dealing with these things for some 40 years. The original pistons were just a different alloy than the block probably just a higher silica content. In reality the piston doesn't persay "wear" the cylinder-the rings do. The piston skirt does come into contact with the cylinder but only due to the rocking effect so a fuzz at the top and moreso at the bottom of the skirt and just gets worse as the ring wear area opens up so the piston rocks more. Yea there is expansion and rates of expansion and all that but that is taken into consideration with piston to wall clearance. It really doesn't matter what the piston is coated/plated with other than to keep the skirt from getting galled but that's why we put good clean oil in them-it's not a zero clearance fit. I guess I just figured this was as good of a place as any to set the record straight on this matter. As far as the valve guides-the best way is just to insert the tapered pilot for whatever seat cutter is going to be used and I will bet it bottoms and still moves around. I have YET to see an HS40 that the exhaust guide wasn't sloppy and didn't need the OS stem valve.
Here is what the cylinder should look like when done-you don't need any fancy machines to do this-at least I don't. This is an actual 1971 HS40 I am currently getting back in order with the +.020 as yours.
This should be the end result of the seats-notice the 3-angles and seat width of .050" all done by HAND and centered on the face-
Here is what the cylinder should look like when done-you don't need any fancy machines to do this-at least I don't. This is an actual 1971 HS40 I am currently getting back in order with the +.020 as yours.
This should be the end result of the seats-notice the 3-angles and seat width of .050" all done by HAND and centered on the face-
Oh and since KK brought it up-Rings. I deal with an artest in NM by the name of Frank C. Bowman. He is in my as well as many others opinion the guru when it comes to piston rings since he can and will make them for anything you can possibly think of and they will be actually better than factory. Low tension BUT ROUND as your cylinder should be. Pretty certain he makes them ALL of ductile iron but he can tell you more if you are truly interested. There is no need to have a hi tension "tight" ring in any engine unless you are just trying to compensate for wear-they do no more than cause more wear and produce friction. The purpose for a piston ring is to seal-period. If you need to contact him I will give you his email or you can probably find it by searching Ringmaster or his name. The work I have had him do for me was absolutely perfect and I am hard to please-also much cheaper than I expected for custom work.:thumbsup:
Chevy Vegas used a Hi silicon content in the casting...then the bore was etched to leave a silicon surface for the piston/rings...
http://yarchive.net/car/vega.html
http://yarchive.net/car/vega.html
Funny-they did just the opposite of Tecumseh. Now with GM as stated in the article their engine had a long stroke, a HS40 does not. The Vega engine was put into a daily driver-Tecumseh's was not. Yea we can argue/agree or just plain discuss this 7 ways to Sunday but in the end WE are trying to restore something that WAS put into production some 40 years ago wether the aluminum/aluminum engine is right/wrong or indifferent but in the end we are all just trying to salvage the past and I am hoping to shed some light on a lot of misconception and or false information. I KNOW what I have stated is the most accurate and detailed information I can offer to anyone wanting to restore a HS40. THESE engines were NOT notorious for failure-they just basically wear out, like anything else. BUT a buttload of them have withstood the test of time and I have seen what and where the problems arrise and I am confident that if properly rebuilt and maintained these engines can and will outlive most of us.:thumbsup: