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Tecumseh Degrees of Timing


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  #11  
Old 01-26-2018, 04:01:36 PM
Andrew Mackey Andrew Mackey is offline
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Exclamation Re: Tecumseh Degrees of Timing

Nice job relieving the steps on the valve passages. Did you leave the directional ramps in place? They help direct the gasses in and out. You might find a performance change with the alteration on the inlet side - changing the passage changes the swirl pattern, which changes the fuel air distribution. It may cause carburation issues. You might want to see if aftermarket valve spring retainers are available. The originals probably will not stand for the high pressure your new springs provide, nor the higher RPMs the engine will develop. If you have not already, you might check into titanium valves. Lighter, stronger, less prone to head/stem separation. Yes, I have seen Techumseh engines with valve heads that broke off - not a pretty sight when a valve head goes thru a piston or blows the head off the block! Did you re-deck the block? If so, be sure you have enough valve to head relief clearance, especially if you use a high rise cam. You should leave a minimum of .015" just in case! You don't want the piston head extending out of the cylinder either. One reason the ALF junior V-12 engine blocks cannot be decked - the heads of the pistons already come flush with the block at TDC, from the factory. Only piston head and valve head clearance to the heads - the width of the head gaskets (about .020")!
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  #12  
Old 01-27-2018, 03:19:36 AM
delray delray is offline
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Default Re: Tecumseh Degrees of Timing

yes andrew, not much porting you can do on this little motor unless in get into rewelding areas. the casting can be real thin on the back side of the bowls and the inlet of the intake is plenty big enough to flow air for this engine that is only turning 4500+ rpm's. so i did not touch that small area or the end of the exhaust port(threads). i do plan on in the future building a newer flathead that has electronic ignition and has dual bearings....YES factory dual bearings on the crankshaft. that engine with get the full treatment. reweld the ports,ss valves with the narrow valve stems....just ton of things i will change on it.
not sure if you read my posting right earlyer on retainers? i do have aftermarket retainers and keepers installed. i use the briggs animal racing retainers and keepers. same design has a automotive retainer.
there is couple different kinds a person can use.
first type are the briggs animal ones. i like these the best. bolt in and go and fit the factory 16 pound springs perfect. second kind you can get a set of dynocams retainers but you will need to machine the second step off little to clear the animal spring or the tecumseh motorsports retainers(heavy duty) ideal for something with a 26 pound or stronger spring.

you also mention about milling the block or head. that would be a big No on that. i might check the head when i get it from the owner and see how straight it is? not a real big fan on cutting down this area? from most info i have read on this area you could harm the flow and being it's only turning 4500+
the engine should still see a little difference in compression with a .080 larger bore. also going to use the stock type steel head gasket with just a lite coat of copper spray on it and i did notes the gasket will also need little trimming on the inside edge. maybe .030 to clear the oversize bore.
for the cam lift i am only seeing about .037 more lift over the factory vintage cam. nothing crazy like a racing cam could be. .070 or more+
the valve springs i am using would still be considered a soft or lite spring.
factory spring might be around 10 pounds and the spring i am using is 16 pound and i really don't want to get much stiffer then that. the cam is more then likely not heat-treated so i don't want to eat it up with a very stiff spring. and a 16 pound spring will not float at 4500+ rpm's.
i was not really planning on posting this project on this forum because it was being posted on another forum already and was just looking for any info on timing (advancement) for points ignition. i do appreciate guys on any info you have gave me on this and i new if i came to this forum i would here from guys that work on these hs-40's back in the day. i don't get that on any other forum. i will try to keep you guys up dated.
minibike forums are now on how can i get my harbor freight 212 engine in my baja minibike(china)...something wong.
here is a youtube link to my ohh-tecumseh motor i built last summer for one race that i drag race on 125ft clay track. i was so impressed with this engine. it was smoking honda's and 212 engines. my plan's this year to build a better one ... kept it kind of rat rod with the old paint job that the bike came with . besides nice paint jobs don't make it faster..
https://youtu.be/Ue-4HkKUTNE
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  #13  
Old 10-19-2018, 11:28:34 PM
delray delray is offline
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Default Re: Tecumseh Degrees of Timing

hey guys I don't get much on this forum a lot,but I though some of you Tecumseh guys would like to see what I built this summer...
https://www.oldminibikes.com/forum/t...-40-build.html
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  #14  
Old 11-14-2018, 03:40:22 PM
delray delray is offline
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Default Re: Tecumseh Degrees of Timing

new forum lay out.
maybe this will work better for now. wont be surprise if it changes again..
https://www.oldminibikes.com/forum/i...-build.161335/
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