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my brother dragged his poulan pro 8.5 hp flathead engine snowblower over the other day with what the repair shop said was low compression. i put a gage on it and it has 30 psi using the rope. he was complaining of it not having the power it used to have and he said it sounds like the engine is slowing down when it gets into a snow load.
so i first hooked up the tester and did a dry test 30psi then i pumped 5 pumps of oil and pulled the rope a few times to get the oil around the cylinder and i had 35psi then i put oil on the valves and the same 35psi
so i went to my 9hp tecumseh flathead and i got about 40psi and no change with oil
so i went to my ohv tecumseh and did the same and got about 50 psi
so i'm thinking this is due the the decompression causing the low compression for cranking with the rope and the electric start.
he thinks he wants me to rebuild the engine which is rings and i may grind and lap the valves, but i wonder if i should be looking at the decompression on the cam? i looked thru the plug hole at the valves and the exhaust looks a bit dark around the seat and on my 9 hp flathead it had a bit of a ring that tells me that valve is seating.

today i will tear it apart and take a closer look but i'm leaning on valves and not rings. but because i have it apart i will do rings also being they are cheap and it is apart

but dos this sound more like the valves and maybe the cam decompression?

thanks

Snow throwers are not used a lot in most cases, but that engine is probably old enough to have issues with the valves clearances closing up and could be floating the valves. Take the head off and then push down on the valves and see if you can turn them with thumb pressure with them in the closed position.

the head is loose or the valves need adjustment, or both. I went thru the same thing on a flat head pressure washer about six months ago. Compression went from 30 PSi to 70 PSI cold. Factory spec on my old pressure washer new is 70 - 80 PSI cold. Even with worn valve guides it runs much better now. If it has a choke, make sure it is off when you test again and the throttle on full open if it has multiple positions.

no the head was not lose. the gasket was sealing perfect all around and i had to scrape it off and there is no valve adjustment on this engine. it is just a horizontal lawn mower type engine. although the exhaust valve guide is wobbly but in the parts listing i do not see valve guides. the cam exhaust decomp looks to be intact and the little pin that holds the valve open during cranking is loose enough for the lifter to push it back down out of the way

i'm leaning on the exhaust valve being wobbly to not be seating real good. and i checked the carb and it is clean on the inside, he said he drains the tank and runs it out of gas every spring.

the rings have top ring .020 center ring .024 oil ring .035 piston is 3.09 dia bore is 3.12 so that all looks good. i did notice the coil to be rusted a bit so it is possible it may have prr spark. anyway he wants new rings and if i can figure out how to get the valves out so i can grind them and lap them i will do that. so far i can't do the exhaust guide because i ahve not found the part. if someone know of these being replaceable let me know the exhaust valve wobbles maybe 1/16" or a bit more

You are wrong, you adjust the valve to lifter clearance by grinding the valve stem. Valve clearance should be .008“-.012”. This manual may be of some help. https://www.mymowerparts.com/pdf/Te...L840-HXL850-TVS840-TVXL840-ENGINES-694988.pdf. I hope you didn’t remove the magneto assembly, because if you did, you will have to retime the engine. Procedure is in the manual and I hate to say it, not easy unless you are an experienced mechanic.

ILENGINE said:

Snow throwers are not used a lot in most cases, but that engine is probably old enough to have issues with the valves clearances closing up and could be floating the valves. Take the head off and then push down on the valves and see if you can turn them with thumb pressure with them in the closed position.

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yes i can turn the valves by hand, the exhaust has maybe 1/16" side wobble the piston is 3.009 dia the bore is 3.12 dia the top ring has the end gap at .020 thecenter at .024 the oil ring is at .034 i have not measure the valve stem dia yet but they do not look worn or scratched up the intake wobbles a bit but that most likely is normal for when the engine heats up. but the exhaust i believe is just to much. if it were my corvair with that much i would be replacing it. both air cooled.

i see the intake has a 1/16" ring around the head of the valve where it has been seating but that is at the bottom of the seat. and the exhaust has something that looks like a tiny shiny ring around the most bottom of the seat. if it turns out i have to leave the guide alone and just regrind the valves i will be putting the seal at the top of the valve for a better interference. the ring gap looks to met to be serviceable. but i will put in new rings because my brother wants new rings.

Rivets said:

You are wrong, you adjust the valve to lifter clearance by grinding the valve stem. Valve clearance should be .008“-.012”. This manual may be of some help. https://www.mymowerparts.com/pdf/Te...L840-HXL850-TVS840-TVXL840-ENGINES-694988.pdf. I hope you didn’t remove the magneto assembly, because if you did, you will have to retime the engine. Procedure is in the manual and I hate to say it, not easy unless you are an experienced mechanic.

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yes i know that what i'm telling you is i have to grind the valve faces and seats because they are not making good contact the intake has .309 and the exhaust has .306 for stem dia. and then i may have to adjust the clearance after i grind them.
. yes i did and i know how to time them thanks there not much to that as the mag fits one way and i have to set clearance. i have brass gages for that or may just use a business card as most are the correct thickness.

Are you saying that you have an external coil assembly? If so then you are correct, but if your coil is mounted under the flywheel, then setting the point gap will not time the engine. If you look in the manual you will find a timing procedure, which involves using a dial indicator and either a buzz box or VOM. Most Tecumseh SnowKing engines used internal mounted coils. If you would supply us with the model and spec numbers we would know exactly which engine you have.

sounds like the engine is already apart. Normally the head comes off, the valve spring gets compressed with your own tool or an inexpensive one you can buy, then the keeper comes off. The valve to tappet clearance gets measured, usually at a specific piston height past TDC then the tip end gets evenly ground on a fine cool grinder wheel until the clearance is in spec. If you gently rock the valve when it is about 1" high off the deck you can feel the guide play. These flat head engines are not worth the PITA to replace guides unless you already have the tool set to ream them out and press in new guides. It is not a car that you will drive 100.000 miles more. All you need is it to run well when blowing snow or whatever. If you want to rebuild it, do it because it is hobby, not to save money. You can buy a new engine for less than to properly re-manufacturer the old one. If you just do a new head gasket and valve adjustment your compression should be fine, unless the cylinder is scored.

sgkent said:

sounds like the engine is already apart. Normally the head comes off, the valve spring gets compressed with your own tool or an inexpensive one you can buy, then the keeper comes off. The valve to tappet clearance gets measured, usually at a specific piston height past TDC then the tip end gets evenly ground on a fine cool grinder wheel until the clearance is in spec. If you gently rock the valve when it is about 1" high off the deck you can feel the guide play. These flat head engines are not worth the PITA to replace guides unless you already have the tool set to ream them out and press in new guides. It is not a car that you will drive 100.000 miles more. All you need is it to run well when blowing snow or whatever. If you want to rebuild it, do it because it is hobby, not to save money. You can buy a new engine for less than to properly re-manufacturer the old one. If you just do a new head gasket and valve adjustment your compression should be fine, unless the cylinder is scored.

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Some of those older Tecumseh engines didn't have replaceable valves guides. You reamed the guide out to a larger size and then replace them with oversize stem valves.

i have both but the one under the flywheel is for the generator. and it works the light the mag is on the outside.

tell me it seems that the loss of power he is having may be do to the valves.the intake is seating completely around the seat but the exhaust is only a hisr think shinny ring that is maybe half way around the seat. and the exhaust valve is all crusty looking like it has not seated in years and the guides are real sloppy as per some YTs so it seems tecumseh does not make new guides and i do not know if b&s has any that may work. so to fis this does tecumseh have over sized valve stems and then you ream the guides to fit the new oversize valve stems? and then i guess maybe new to spring guides that have to seal in them, but the oversized valve stem amy just work if these are made. the current valve stems are .309 intake and .306 exhaust. so if i can get over sized stems and ream the guides that would be about the same thanks

ILENGINE said:

Some of those older Tecumseh engines didn't have replaceable valves guides. You reamed the guide out to a larger size and then replace them with oversize stem valves.

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thanks i found out they are not replaceable. i wonder if the guides were put in the diecast mould before it closed for the shot so the guides were moulded into the casting? anyway i found out they make an oversized stem for this so if anyone has one i sure would like to get one. outside of that i'm now getting some car guys on a fourum to see if they have any car valves that have these numbers the i can make fit

sgkent said:

sounds like the engine is already apart. Normally the head comes off, the valve spring gets compressed with your own tool or an inexpensive one you can buy, then the keeper comes off. The valve to tappet clearance gets measured, usually at a specific piston height past TDC then the tip end gets evenly ground on a fine cool grinder wheel until the clearance is in spec. If you gently rock the valve when it is about 1" high off the deck you can feel the guide play. These flat head engines are not worth the PITA to replace guides unless you already have the tool set to ream them out and press in new guides. It is not a car that you will drive 100.000 miles more. All you need is it to run well when blowing snow or whatever. If you want to rebuild it, do it because it is hobby, not to save money. You can buy a new engine for less than to properly re-manufacturer the old one. If you just do a new head gasket and valve adjustment your compression should be fine, unless the cylinder is scored.

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yes i know but the guy that need this has no money to pay for a new or rebuilt engine. so i will get this going one way or the other. i measured the guides and the intake is good but the exhause is 5/16 so now i'm looking for a car valve that is the same or close for the head size and the stem is 5/16 .312 and the stem is 4" with the retainer ledge at 3.66" from the top of the head. i can grind the keeper to fit and regrind the valve thanks

On these type engines i don't rely on compression tests. I use a leakdown tester. One of the benefits is that you can tell immediately if it is rings or valves.
The worn exhaust valve guide is a common problem Briggs and Tecumseh L head engines. Unless the guide and valve are badly worn if you just lap them in the engine will run fine but with some occasional popping in the exhaust. If the valve stem is worn you can fit a new OEM valve to help. Unless you have a reamer that matches a larger diameter stem i doubt if a different valve will work as the guide is not worn round or straight top to bottom.

ok i found out from my former son in law that has a repair shop that i can't get even the case for this engine. so he found me a nos oversize valve and so i will just rebuild this engine. i posted the dia gram just in case some here know of other valves that are similar. but for now i'm ordering rings a gasket set and seals and will work on this until i find a workable valve or at that time just get a nos valve. thanks

Hammermechanicman said:

On these type engines i don't rely on compression tests. I use a leakdown tester. One of the benefits is that you can tell immediately if it is rings or valves.
The worn exhaust valve guide is a common problem Briggs and Tecumseh L head engines. Unless the guide and valve are badly worn if you just lap them in the engine will run fine but with some occasional popping in the exhaust. If the valve stem is worn you can fit a new OEM valve to help. Unless you have a reamer that matches a larger diameter stem i doubt if a different valve will work as the guide is not worn round or straight top to bottom.

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thanks i can't tell if the guide is worn out equally all around but if i get a ne oversize valve i may be able to ream it out if not it will be better than the wobble i now have. thanks

Hope you get it running. The main reason for the exhaust guide to wear is because the engine is not run hard enough. The engine needs to get hot enough to create an oil mist inside the engine which lubricates the valves. Since no oil pump and the oil slinger doesn't sling oil into the valve chamber the engine on snow blowers need to be run at full throttle and run hard to get the temp up to where it needs to be. Worn valve guides is a common problem on old snow blowers because it is hard to get them up to temp. Newer OHV engines do better on snow blowers.

if you look close at these valves you see the intake has a brighter ring on the face that is the seal but the exhaust is all full of crud that is not sealing. i could re grind it and lap it in but because of the wobble i believe it would become this way again real fast.

Hammermechanicman said:

Hope you get it running. The main reason for the exhaust guide to wear is because the engine is not run hard enough. The engine needs to get hot enough to create an oil mist inside the engine which lubricates the valves. Since no oil pump and the oil slinger doesn't sling oil into the valve chamber the engine on snow blowers need to be run at full throttle and run hard to get the temp up to where it needs to be. Worn valve guides is a common problem on old snow blowers because it is hard to get them up to temp. Newer OHV engines do better on snow blowers.

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your correct but what you going to do they run in the winter. but tecumseh might have made the guide hard and the valve to be the wear point so that you replace the valve and your done. it is far easier to change out a valve than to punch out the seat. but it is what it is. at this time i have a handle on a oversize valve but also still looking for a car type valve. i have an old corvair valve that i could regrind the stem and head and redo the keeper but the seal surface has a divit that is just to deep to make it work. if i could find a alve that was 4" long and had the 5/16" stem and the1 1/8 or a bit bigger head i would make that work. thanks

the valves stretch. Once that happens the clearance goes away and they never shut. I glass beaded my valves with high quality fine beads like I used to do in the machine shop, or you can wire brush them. Use a little lapping compound and a hand lapping tool after you adjust them. Then check the adjustment again. I had to grind quite a bit more than I thought I might on mine to get the spec clearance. They the compression came right back up to normal. It is a lawn mower engine. They aren't made to be fully re-manufactured. The cost of a new engine makes re-manufacturing one uneconomic. The valve guides are crappy. Some engines you can get replacements that you bore the guide hole, then ream it then press in a false guide. Others as stated the guide simply gets reamed then an oversize stemed valve is used. These engines are old so parts are getting scarce, and in some cases expensive. Many times a replacement engine or snow blower is less expensive. And in states like California they want you to use an electric or battery powered one.

corvairbob said:

if you look close at these valves you see the intake has a brighter ring on the face that is the seal but the exhaust is all full of crud that is not sealing. i could re grind it and lap it in but because of the wobble i believe it would become this way again real fast.

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If you can get a replacement exhaust valve do so. If you have a real valve grinding machine put a lite resurface on it, then tip it to get the correct clearance, then hand lap it. It is a lawn mower engine and not worth buying the tooling to screw with the guides. If you decide to go that route then next you will want to bore the engine, go to an oversized piston, replace the rod and maybe crankshaft and when done the cost will be 3X what a new engine might have cost you. How many years old is the snow blower now? My pressure washer, was slightly better, I hand lapped the valve and it cleaned up enough to seal well although the guide was really worn, its power came back. It is 25 years old. I won't live that long for a new one.

sgkent said:

the valves stretch. Once that happens the clearance goes away and they never shut. I glass beaded my valves with high quality fine beads like I used to do in the machine shop, or you can wire brush them. Use a little lapping compound and a hand lapping tool after you adjust them. Then check the adjustment again. I had to grind quite a bit more than I thought I might on mine to get the spec clearance. They the compression came right back up to normal. It is a lawn mower engine. They aren't made to be fully re-manufactured. The cost of a new engine makes re-manufacturing one uneconomic. The valve guides are crappy. Some engines you can get replacements that you bore the guide hole, then ream it then press in a false guide. Others as stated the guide simply gets reamed then an oversize stemed valve is used. These engines are old so parts are getting scarce, and in some cases expensive. Many times a replacement engine or snow blower is less expensive. And in states like California they want you to use an electric or battery powered one.

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yep i know but i did have proper clearance on them so they did now stretch to much this time. but is you saw the seat there is a hairline area about halfway around the block seat that is there this valve was hitting. and because of the wobble it had i do not think the valve had time to completely seat before it had to open again plus if you notice the divit in the seat? but that might be just dirt i have to recheck it today to make sure. but notice the hailline sealing this did and it is only about halfway around the seat. there is not enough there to do a seal at all. plus i now theya re cheap for some folks but some people just can't afford new engines when they take a dump. this is for my brother and he just has no money to spend on engines. thanks

We don't control the economics. If you want to buy the tools to go to oversized valves and guides, or you have them already then go for it. Otherwise, why flame the messenger? I spent a good 5 years working in a very well known automotive machine shop in the racing and service fleet world in the late 1970's and early 80's so I understand clearly what is involved with loose valve guides and seating. The guides in these engines are not designed to be serviceable but they can be. The engines were designed to be throw away's when the mower, snow blower, log splitter, pump etc., wore out. The seat and valve on your engine was damaged by a carbon build up. The valve probably never fully closed and exhaust gases did their erosion. The other option is to find another 8hp engine in better shape and swap it. No home brew tool is going to fix what you are trying to do. To surface the seat beyond a hand lap you need a tight guide and the right tools. Just finding the right stone or cutter for that seat may be an expensive pain itself if you do have access to valve grinding tools.

thanks i got the intake done and will do the exhaust when the part gets here. the cylinder honed out good the rod is in good shape the crank is in good shape. so i do not want to take a chance on a used engine as that may be in the same condition. so based on what i have in front of me i got rings an oversized exhaust valve and seals and a gasket set. that will do what i need it to do. yes i might get lucky with another junkyard engine but i will not take that chance. if my brother could afford a new engine i would be locating him one but he can't and i'm not paying for it. i will rebuild this one and it should be good to go. i have done my share of car engines so this is just a real small car engine if it was my engine i would have re ground the valves and put it back together but he does not want ust the valves so he wants it rebuilt. thanks lots for the ideas. what i was looking for was the guide help but it seems these are not really replaceable so now to use the oversize exhaust valve and just use it.
thanks