HS50-62023 - Compression question

#1
Any one know the proper compression reading for a HS50-67023. Just rebuilt one with new rings(measured proper gaps and gaps spaced properly), cyclinder honed, valves lapped, valve guides w/in specs, valve gap w/in spec. Im only getting about 60 psi. Shouldnt it be more than that?
 

cfh

Well-Known Member
#3
with the bump compression release it's hard to get a reading, but that does seem low. i've heard if you spin the motor in reverse you can get a good compression test. personally i grind off the bump on the cam. but that's me.
 
#4
with the bump compression release it's hard to get a reading, but that does seem low. i've heard if you spin the motor in reverse you can get a good compression test. personally i grind off the bump on the cam. but that's me.
I had no idea there was a compression release. Do you have a pic of the bump you grind off for the compresson release?
 
#6
Interesting...always wondered why that was there. I havent actually run the engine since the rebuild...just noticed that compared to a Briggs 5HP I just rebuilt eariler..there was no need to search for the compression stroke before pulling the cord...seemed too easy. Thats why I did a compression check before giving it fuel. We'll see what happens
 
#8
I used a bench grinder remove the "bump". a Dremel Tool or a bastard file would work ass well. The steel is the cam is not very hard and was very easy to remove.
Using a sanding tape might work but you really need to be aware to keep the cam surface as round as possible.
 
#9
Dremel with a grindstone. If you remove it you will have to limit how you start it. You have to slowly pull it over till top of compression then yank it otherwise it will eventually break the shroud or rope.
 

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#10
3m makes some hard wheels that can grind/polish that little bump right off and not damage the cam at all.
just make sure you run little zinc in your oil.
 
#11
I used a bench grinder remove the "bump". a Dremel Tool or a bastard file would work ass well. The steel is the cam is not very hard and was very easy to remove.
Using a sanding tape might work but you really need to be aware to keep the cam surface as round as possible.
Thanks man...big difference...95psi now! Now what’s this about running some zinc in the oil?
 
#13
3m makes some hard wheels that can grind/polish that little bump right off and not damage the cam at all.
just make sure you run little zinc in your oil.
Hey Delray - after grinding off the bump...I used a fine grit emery cloth to smooth it. Should that be sufficient...or should I still use some zinc in the oil...and where do I get zinc?
 
#14
long as you got the grind marks polish out you should be ok. some oils still have the zinc in it. for example diesel oils. for me i like to run a 5w-30 oil and then add little lucas zinc additive(4oz) and the rest oil. lucas stuff comes in a 16oz bottle. for example on a tecumseh small block takes 21oz. so 17oz of oil and 4oz of zinc product. personally never add over 20oz after the engine been ran and then drain(oil) you will always have a good 1 oz still in the motor and if you plan on running higher rpm's then stock? then keep it closer to 19 oz. 21oz will pump it right out the breather vent when reving it in the high rpm's.
and yes zinc we help protect the cam. engines are always fun to play with when making mods to them......:scooter:
 
#15
Why wod you need to change the oil? You ground down the compression bump on the base circle, that is when the lash is open and thereos zero spring pressure there.
 
#16
If you referring to adding the zinc oil. Not so much to do with the repaired area. More for over all protection. With more oil companys now taking this out. It never hurts to have this in your old flathead engines..:scooter:
 
#17
In my photo of the bump being ground off, it took very little effort to do it as the cast iron is soft. Emery cloth or a fine grit sand paper will polish the surface with ease.
If need be use a Mobil-1 type oil if you think it is necessary.
In 55 years of running small engines on my mini bikes I have never had a part fail due to an oil problem.
I run 30 weight in the hot summer and 10W-30 in the winter months.
With most engines using a quart or less of engine lube oil and no filter being used, I change it every time after a hard run of 25 miles or ten hours of run time. My engines last.
 
#18
If need be use a Mobil-1 type oil if you think it is necessary.
In 55 years of running small engines on my mini bikes I have never had a part fail due to an oil problem.
I run 30 weight in the hot summer and 10W-30 in the winter months.
With most engines using a quart or less of engine lube oil and no filter being used, I change it every time after a hard run of 25 miles or ten hours of run time. My engines last.
and you shouldn't had any problems in years pass with a small engine. back in the day when flatheads where new, oil had zinc in it and help save this little components when first fire up(break in). now when you start to modify them with heavier springs and more rpm's it becomes a different story and with the engines you have played with in the pass all had soft springs and where governor. making it less hard on the components to fail.
Now with guys hot rodding a flathead and even worst a clone motor you should run a zinc in your oil.
mobile-1 (high mileage) synthetic oil has zinc in it and is a good alternative racing oil for the gokart guys that really can't spend money for racing oils or just want to buy something ready and available over the counter any parts store. for me i run 5w-30 only on my engines that turn good amount of rpm's.(performance engines) thinner oil works better in tight clearance areas over heavier/thick oils do.
stock governor motors you can run anything in them they don't know difference...lol
 
#19
His is a stock motor. even new oil has zinc just less of it. His question on oil seemed to be related to the fact that the cam was soft there. My point was there is zero lifter pressure there.
 

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