new sbh engine build.
- Thread starter anthonyg9819
- Start date
They are like a ball park hot dog "They plump when you cook them" 
And yes, today I actually took a propane torch to a used small frame Tec Exhaust valve to see what would happen (its going in the garbage anyway)., expanded it by .002 just heating the stem right in the port area.
And yes, today I actually took a propane torch to a used small frame Tec Exhaust valve to see what would happen (its going in the garbage anyway)., expanded it by .002 just heating the stem right in the port area.
Yea its normal slop, I will say however that if you are really getting and honest .251 out of the guide, it is measuring larger than normal by .001-.002. An no I am not just throwing mythical numbers out there, I actually pulled some blocks out and did some measuring:
Far left engine is an NOS HS50 from 1994 (with the small taper BB crank though, built to replace 1972-1980 engines0. The three HS40s next to it are extremely low run time blocks, I think 2 of them may have been training engines from Belsaw. the far right one is the one I mentioned earlier that had been stored in a wet environment, I did some hone work as it had some spotting on the cylinder wall from it. I also did check a whipped HS50 block (needs bored oversize) not shown
with that said, all those exhaust valves, and there are 3 different versions form mid 70's-mid 90's all came in at .244 even the batch of NOS ones at the bottom left measured out the same. Tecumseh DID NOT MAKE a .248 sized exhaust valve with that style keeper. The real early pinned valves I think may have been thicker, but that's not gonna help. there are some .246 but I'll get to those at the end.
The guides measure in on the new/next to new blocks at .249-.2495 range, there is a used but clean HS40 (top right in photo) that comes in at an honest .250 and the whipped HS50 block (not seen) came in at .250.5/.251. I used the standard Neway 1/4 pilot and a briggs .250 finish reamer as guides as well as 2 different dial calipers. the briggs reamer comes in at .250 exact on the cutter end so it would not go into the any of the 4 blocks in the front measuring under the .250, that HS40 top right It would go but have to twist to get it through and the whipped HS50 would go with light twist (no force though and could feel very slight movement. when it was all the way through.
with all that said, common spec is .004/.05 for the Tecumseh EX side, this is also the same on the small frame H engines as they shared the same exhaust valve.
Regarding the .246 size, I found a used one here; Its fresh out of a 1967 H35 I started to rebuild and its the original. It is a 29313 (the same part number used through 1996/97. The only time I can remember finding that sized valve was in the late 60's engines. I think they shrunk them down to the .244 size into the 70's, that kinda goes along with them going to aluminum bore only for the most part on the small frames and the introduction of the HS50 but I don't know if size reduction is connected to that or not. That part number did get revised a few times (29313b/ 29313c) Best chance to maybe find one new would be to look for the old style scripted box and probably the 29313 number only on it, I put an early box (its an intake valve actually in that one) on the table just to the right of the loose valves so you can get an idea of the style, the boxes for the loose valves on the left are the 1970's into 80's era parts boxes-those are 29313c. And I am taking a stab that you will get a .246 valve as I do not know for sure so don't blame me if its not that size I think one of the revisions or alphabet letters just indicates it comes with the keepers for both H/HS40 and HS50 as they are different (so those are post 1972 made)
Oh yea, that crusty valve on the burnt block of wood on the table was my "Heat test" valve In my late teens me and my buddies bought a bunch of yard/fun karts, we would do midnight runs during full moons on paved golf course trails and dirt roads out in the boonies. I just followed the glowing red dot that was the exhaust coming out of the pipe of my buddies 5hp B&S when we would hit the straights and he would start to walk away with his big tire kart......they do get pretty warm, made for a good tail light!
Far left engine is an NOS HS50 from 1994 (with the small taper BB crank though, built to replace 1972-1980 engines0. The three HS40s next to it are extremely low run time blocks, I think 2 of them may have been training engines from Belsaw. the far right one is the one I mentioned earlier that had been stored in a wet environment, I did some hone work as it had some spotting on the cylinder wall from it. I also did check a whipped HS50 block (needs bored oversize) not shown
with that said, all those exhaust valves, and there are 3 different versions form mid 70's-mid 90's all came in at .244 even the batch of NOS ones at the bottom left measured out the same. Tecumseh DID NOT MAKE a .248 sized exhaust valve with that style keeper. The real early pinned valves I think may have been thicker, but that's not gonna help. there are some .246 but I'll get to those at the end.
The guides measure in on the new/next to new blocks at .249-.2495 range, there is a used but clean HS40 (top right in photo) that comes in at an honest .250 and the whipped HS50 block (not seen) came in at .250.5/.251. I used the standard Neway 1/4 pilot and a briggs .250 finish reamer as guides as well as 2 different dial calipers. the briggs reamer comes in at .250 exact on the cutter end so it would not go into the any of the 4 blocks in the front measuring under the .250, that HS40 top right It would go but have to twist to get it through and the whipped HS50 would go with light twist (no force though and could feel very slight movement. when it was all the way through.
with all that said, common spec is .004/.05 for the Tecumseh EX side, this is also the same on the small frame H engines as they shared the same exhaust valve.
Regarding the .246 size, I found a used one here; Its fresh out of a 1967 H35 I started to rebuild and its the original. It is a 29313 (the same part number used through 1996/97. The only time I can remember finding that sized valve was in the late 60's engines. I think they shrunk them down to the .244 size into the 70's, that kinda goes along with them going to aluminum bore only for the most part on the small frames and the introduction of the HS50 but I don't know if size reduction is connected to that or not. That part number did get revised a few times (29313b/ 29313c) Best chance to maybe find one new would be to look for the old style scripted box and probably the 29313 number only on it, I put an early box (its an intake valve actually in that one) on the table just to the right of the loose valves so you can get an idea of the style, the boxes for the loose valves on the left are the 1970's into 80's era parts boxes-those are 29313c. And I am taking a stab that you will get a .246 valve as I do not know for sure so don't blame me if its not that size
I think one of the revisions or alphabet letters just indicates it comes with the keepers for both H/HS40 and HS50 as they are different (so those are post 1972 made)Oh yea, that crusty valve on the burnt block of wood on the table was my "Heat test" valve
In my late teens me and my buddies bought a bunch of yard/fun karts, we would do midnight runs during full moons on paved golf course trails and dirt roads out in the boonies. I just followed the glowing red dot that was the exhaust coming out of the pipe of my buddies 5hp B&S when we would hit the straights and he would start to walk away with his big tire kart......they do get pretty warm, made for a good tail light!markus. well executed. my problem really put you to work. must have spent quite a bit of time on that, i did not know they had so many valve stem changes. i thought there were two. early 70s and the newer style i have now plus the 1/32 over. yes my guide is an honest .251. i put the 1/4 plus 1 pilot in and there was a slight movement. i carefully cut a piece of 0.0015 feeler gauge and slid the pilot in the guide with it. i measured were the taper on the pilot turned to the full with and marked it with a sharpy. i did not force it. it slid in nice and snugged up the pilot. so my original estaminet of 0.007 was wrong is like 0.0085. i bought 2 more quality reamers and a third pilot today. also a 1/32 over ex valve. i don't like the fat stem but can't replace the guide. im gonna go for 0.004 if it hangs up i will take it to 0.005. thanks for all the measuring. anthony.
markus says they don't make a .248 then they don't. what was the over size valves that Tecumseh made for worn out guides? being your a machine at one time. if you could get to a lathe you could machine a briggs valve like ole4 did and stuff it in there. not sure if there big enough either. the ones I got are new ss flathead briggs valves and they only mic out at .247
When you get the 29315 OS valve I would like to know what the stem measures at to get an idea of what kind of clearance to expect. The 1st over brass guide inserts for Briggs gets reamed to the same size as the OS tec valves do. I had bought that size reamer and centering guide etc.. from Briggs and did some of those inserts in the last briggs 3hp's I did. I have not tried the reamer in the steel Tec guides though. An engine just came in and has a block thats not repairable, so I may try the reamer on it and see how it cuts it since the block is junk. I dont know if it would be acceptable to use the B&S brass insert pressed into the steel guide, but that would open up both options, Insert or the OS valve.
Below is the 29313 I purchased that was the .2450 stem for my H30. still has one left.
http://rover.ebay.com/rover/1/711-5...0001&campid=5335845805&icep_item=164013902992
http://rover.ebay.com/rover/1/711-5...0001&campid=5335845805&icep_item=164013902992
markus, i know you mention earlier that tecumseh didn't make a .248 exhaust stem. i had a old hs-50 points engine that had a .246 exhaust and a .248 intake. could that intake possibly be a replacement over size valve at one time or another for this hs-50 engine. also looks like it's been in there from day one or at least very long time.
markus, i know you mention earlier that tecumseh didn't make a .248 exhaust stem. i had a old hs-50 points engine that had a .246 exhaust and a .248 intake. could that intake possibly be a replacement over size valve at one time or another for this hs-50 engine. also looks like it's been in there from day one or at least very long time.
Your comparing apples and oranges. As I stated previously in the thread Tecumseh chose to use a smaller OD on the stem on the exhaust side than they did on the Intake for these engines, and as you can see they even reduced that size by .002 on the exhaust stem (while retaining the same part number btw). They also used (like just about every other engine manufacturer) different materials on intakes then they did on exhaust valves. On the HS series engines there's no question which valve goes where due to seat/port size. One big problem though is the H25-35 used equal sized seats and that size was the same as the exhaust on an HS series engine (and they share the same part numbered Exhaust valve). so If you have a bunch of valves laying around Its important to make sure you got the right valve going in the right hole. You could throw an H25-35 Intake valve in there with its .248 stem, but when that valve that's designed to run at much cooler temps and be constantly washed and cooled by fuel vapors fails due to the heat and getting pummeled by corrosive gases, make sure you post up the carnage!
gotta ask yourself, why would Tecumseh reduce that size, and even reduce it more as they years went on? Was there something happening like excessive wear, or sticking?
Maybe it was just the guy running the machine making the valves all those years, intentionally skimming .002 off. Maybe he wore pants that were too long, and folded them up at the bottom....all day he would brush off the extra shavings and they would fall off into the cuff of his pants and he could them out and nobody caught on since the weights of the swarf that the factory accumulated stayed the same....Meanwhile he Retired early (probably about 1997 when they reduced the port size of the exhaust valves on the small frame engines) and cashed out on recycling the material he smuggled out of the factory all those years, moved down here to FL, and bought a fishing boat. Isn't that how it always ends in the movies? boat drinks on the back of a Bertram.......Its the perfect crime!
This is from a Tecumseh repair manual, while it does not give an explanation why, Its goes along well with the subject of valves and something that needs to be done correctly.
I wasn't trying to compare anything, more of a question. as you know I don't really play with the stock stuff when building my flatheads. more into the mod's stuff. but still very interesting to know about the stock stuff too. hard to say why Tecumseh went smaller over the years. I also seen with my ohh stuff the stems are small. I know with working with the new clone stuff the valve stems are very small from 5.5 to 5 mm in size. it would of been interesting to see where Tecumseh would of been today if they where still around.
anthonyg9819, what every size valve you deside on using. for example a small .244 stem or a larger from a briggs. the dyno retainers/keepers you plan on using will still work for either one.
thanks. i hadn't thought about that. dyno cams is short handed on account of the epidemic. i talked to randy two days ago and ordered the springs keepers and locks. they said 5 day turnaround. they have had the cam since last friday and they haven't started it yet. looks like it will be more like three weeks than five days. Anthony.
anthonyg,spending all this money just to fix a loose valve you could of just bought a ss narrow stem briggs flathead valve that comes with a bigger stem and cut it shorter and machine a new keeper grove into it. being that your a machine and with a ss valve they are machine down on the stem area where the air flow's through and are made out of one piece material. not like the stock valves are made of two piece's and are fused together. so when your spinning almost 7000 rpm's and your valve is glowing red hot it won't come un glued like the ss briggs valve......lol
either way the stock valve will work and you will have fun at the end of the day...….
either way the stock valve will work and you will have fun at the end of the day...….
delray. i looked in to the briggs guides and stainless valves when i started my fist hs50 rebuild. i am in spring hill fl now. i have o access to machinery. the local lawnmower shops around hear couldn't even give me a price on reaming a stock valve guide. let alone cutting a briggs valve down machining new keeper grooves and pressing in a new guide. my only problem is i don't like the restrictive fat 1/32 os valve stem. i am thinking of building just ONE real hot hs50 completely opposite my stock appearing period correct look. it will have a square blower cover. non lighted. straight slide carb and header. if i build it i want the briggs ss valves in it and the next size up cam. speaking of cams i got an email last night. it said the cam and all the rest of the parts will be hear friday. anthony.
sounds like a lot of fun in the future. next came they make is a 255 lift and that one is good for another 500 rpm's
245 was rated at 6500 and 255 at 7000 base on a ohh motor setup. my opinion in small hs-40 little higher. now if you really deside to go with a lot of good tricks in your motor you could send a cam off to tim isky and make you a black mamba 275 lift and will pull hard up to 8000+.....maybe 8500 rpm's. big thing is making sure you can get a valve spring to work in the block when going to a higher lift.
245 was rated at 6500 and 255 at 7000 base on a ohh motor setup. my opinion in small hs-40 little higher. now if you really deside to go with a lot of good tricks in your motor you could send a cam off to tim isky and make you a black mamba 275 lift and will pull hard up to 8000+.....maybe 8500 rpm's. big thing is making sure you can get a valve spring to work in the block when going to a higher lift.