I never thought of making my own for my cc 122. I hope it works good.
A T

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since the new gasket is thinner.. I would check the spark plug to see if it will not get hit by the piston or the valves or the block if it protrudes the head too much..

 

I'm not so sure aluminum wont melt...if not,it'll be a high compression engine now!..
I have made a few head gaskets from copper roof flashing,for antique engines no one had new head gaskets for locally...worked OK,but they were a pain to make!..

 

if the aluminum gasket melts.. so would the head.. they r touchin each other & the same material.. now if the head is warped he may get a leak & this could cause a burn thro area..

copper gaskets r used on some brake systems on cars & trucks.. they take pressures a lot higher than a gas engine..

 

I'm not expecting the sheet aluminum to melt...yanno because the head & block are also aluminum, but this sheet aluminum may have a lower melting point than the head & block material, only a working test will determine if this is practical or not.

I double checked the RJ19LM spark plug (because whirly said to, and because it is located just above the IN valve) and with each of the valves fully opened by the cam lobe, I was able to raise each of the valves a full 1/4" more before contacting the head (with homemade gasket in place). So even if a different spark plug were used, it would have to reach nearly a 1/4" more than the stock spark plug, to touch the IN valve.

Hi atlas ten, aluminum is soft, tin would probably work well, copper a little stiffer, and steel is probably a little too hard for my 399cc application.

I may have to break down an buy a new gasket, but not if I don't have too!! hahaha

wwxx

 

I've made a few head gaskets out of really soft copper and soft aluminum. An old time machinist taught me this trick when I was a kid. These were on the old low compression, 6 to 1 and under, engines of the time. Used aluminum paint as a sealer, put on wet and allowed to dry before starting the engine. These gaskets could be used time and again if you did not damage them. Made one of soft copper that I used on a Model A Ford I had in high school. It was still holding when I sold the car several years later.

If the aluminum you are using is too hard I'd suspect you will have some leakage and possible burn thru.

I'm looking forward to what you learn.

Mike

 

Hi Tencubed & tractorholic, if I remember correctly I'm pretty sure Briggs engines are generally around 6:1, and the way their cam is ground with [easy-spin starting TM], the IN valve never really closes completely on the whole of their compression stroke, the cam holds the valve open just a small amount maybe .005", and the IN valve doesn't actually close down until about 10 degrees BTDC of the compression stroke. It is rare to find a briggs with compression over 60 psi, and it kind of needs to stay low, because their electric starters are kind of gutless anyway/plastic pinion gears & such.

I am having thoughts of metallic painting the gasket.

wwxx

 

the intake valve will fully close once the engine turns over at about 400 RPM.. under that the compression release is active till a counter weight on the cam releases it.. it only takes 30-35 PSI to make the engine fire up.. when it does the RPM will increase greatly & the compression will hit as high as 125 PSI..

now the oppisin twins of B & S have a special cam grind that gives it a release.. there is no mechanical release on these engines..

the intake valve on all their engines do close fully..

 

Valves always close, they need to in order to run. You're thinking of the compression release which only matters during the initial start-up. On most engines its a centrifical piece of metal that bumps the exhaust valve so you're not breaking your arm (or starter motor) fighting full compression. Once the engine is running the compression release moves out of the way and the cam lobe takes over.

 

Hi Skin & Whirly, this engine has the Easy Spin type camshaft, which has been used on B&S engines since about 1961-1997. There is no centrifugal mechanism to release compression on these cams, that is the cam lobe profile's job, to be made in such a way, as to not allow the IN valve to fully close during all of the compression stroke, except at the very last, about 15 degrees BTDC, then the IN valve begins to close, and is finally closed at about 5 degrees BTDC of the compression stroke. And bytheway the IN cam lobe profile, compression release is not really affected by speed.

This is commonly referred to as a 'bump', but it is actually an extension of the IN cam lobe profile. Compared to the EX lobe profile, there is no extension/bump... it simply opens & closes.

The IN cam lobe profile does not simply open and close on the Easy-Spin cam lobe profile. The IN cam opens at about 13 degrees BTDC of the EX stroke. The IN valve opens normally to it's full open height during the IN stroke. The IN valve remains open to the bottom of the IN stroke, and well into the bottom of compression stoke, but is still clearly open well into compression stroke.

The IN valve nearly closes at the bottom of the compression stroke, but because of the Easy-Spin cam lobe profile, the IN valve never completely closes during the compression stroke. The IN valve remains slightly open during nearly all of the compression stroke (slightly open, approx. .004-.008" valve lift). At about 13 degrees BTDC of the compression stroke the IN cam lobe profile begins to change, and by about 5-10 degrees BTDC of the compression stroke the IN valve finally closes. [This allows the compression stroke to never build over about 60 psi, as the excess pressure is blown out the slightly open IN valve]

The actual power stroke from TDC and further, reveals the true baseline of the IN cam lobe profile. This is why B&S valve lash is generally adjusted with the piston 1/4" down in the bore of the power stroke, which at that time and not before, has allowed the Easy-Spin profile completely finish. Normally we adjust the IN valve lash, by inserting a .005" feeler gauge (lash of the IN valve cold) at the 1/4" ATDC of the power stroke, the lash will remain .005" for the whole of the power stroke, and most of the EX stroke, until about 13 degrees BTDC of the EX stroke, where the IN valve begins to open again.

You can verify this by simply removing the head & breather of any B&S with Easy-Spin starting, and use a feeler gauge on the IN valve lash area...rotate the engine and you will find what I have described.

wwxx

 

OK.. at the first u speak of a 12 HP model 28.. then u say a 399 cc engine.. just which r u makin the gasket for.. the 'easy spin' models were used on push mowers & tillers.. that 12 hp I don't think was an easy spin unit..

 

Oh I'm sorry, I mis-stated the cc's...from the owners manual page 2, the cc's are 465 for the 28 cubic inch flat heat. (model #28V707 1113-E1) http://bsintek.basco.com/BriggsDocumentDisplay/mssAIQ-K_ny7tH217FzoPu.pdf

I guess I had the cc's mixed up with the old 11 hp model 25 cubic inch flat head, which I think was 399 cc's.

As for believing if it is Easy-Spin or not...what else can I say, except if it wasn't Easy-Spin, the electric starter would not be able to start it, and I suppose there are some of these same 12hp engines [like on a snapper RERider] that have a manual rope start, it would be very difficult to start if it was not for the Easy-Spin feature of the camshaft.

I made a little picture of the IN cam lobe general profile.

wwxx

 

Ah yes, easy spin. Basically just a ramp. Believe it or not but the valve does close completely most of the time when the engine is running. Its so fast that the compression loss from the ramp is practically non-existent.

 

Hi Skin & Whirly,

Well I'm not trying to be argumentative but...the IN valve cannot magically close at some point because of an increase in speed [during the compression stroke], speed has nothing to do with it. A real example of that is, change your IN valve clearance from the recommended .005" lash, to about .015-.020" lash, completely obfuscating the Easy-Spin feature, and the result will become obvious.

The engine will pull up on full compression, and just about jerk your arm off trying to start it, an electric starter will just stop, buzz, & smoke. But lets say you get it started, yes with the engine running, you will have full compression on the compression stroke, and you should even realize a bit more power, because the valve actually closed completely on the whole of the compression stroke.[by changing the lash from .005" to .018"] You will probably have a noticeable change in IN manifold pressures/vacuum pulses, and probably less sooting in the IN manifold itself.

The Easy-Spin is the only reason you can start the engine, it has been used on all of B&S stuff for a long time now, this engine I made the gasket for was built in the year 2000, and still is to this day on anything B&S makes that doesn't have the centrifugal compression release.[twin cylinders come to mind] It is only the centrifugal type compression release that magically gets out of the way once the engine is up to running speed, the Easy-Spin is consistently allowing a small lift & release of pressure all thru the various speeds, true there is only a slight loss of compression at running speed, hardly noticeable I would agree, but the valve cannot close completely if the recommended valve lash is used.

Which brings us back to my original statement in this thread, "...generally around 6:1, and the way their cam is ground with [easy-spin starting TM], the IN valve never really closes completely on the whole of their compression stroke, the cam holds the valve open just a small amount maybe .005", and the IN valve doesn't actually close down until about 10 degrees BTDC of the compression stroke."

Now this is why I like posting stuff at MTF, you can't get in depth explanation [with pictures] of this thing from wikipedia, nor even briggs & stratton.com about something as important as Easy-Spin.

wwxx

 

The simple proof of the pudding of what wwxx is saying is to try to insert a feeler gauge into the IN valvetrain. Find the thinnest you can, and see if it will fit during the compression stroke.
One could find TDC of the compression stroke, and rotate the crankshaft up to 180degrees in the opposite direction, and find where there is clearance. Note the position of the crank in its throw, and then rotate in normal rotation and find where the clearance disappeared.
My impression for all this time is that there was a miniscule bump in the intake cam lobe 'ramp' area, such that a bit of gas was allowed to be released, but the valve itself was closed prior to and after the 'bump'.
I do not have one to perform any measurements upon. A piece of chalk to mark the flywheel screen and the shroud should make this a simple test.
tom

 

That's about right tomwO, except I recommend removing the head [on these flat heads at least] while your using your feeler gauge to take up the slack [lash], in this way you can easily decide the exact moment the valve lifts off the seat.

Because as you know, the valve will not turn with your fingers when it is closed but when the cam profile rises, it will lift the valve, and immediately the valve will spin if your twisting on the valve head with your fingers. [this is with or without springs installed, and as accurate as most dial indicators]

The way we use to do it a hundred years ago, on OHV engines, was to use your feeler gauge for clearance and twist the push rod with your fingers, to notice exactly when the cam profile changes...[while adjusting valve & injector lash, this is an commonly used, old trick] [the other old trick on solid lifter OHV engines was to use your feeler gauge while the thing is running, use 'hot' specifications, adjust rocker nut till the cylinder misses]

I got my engine running...and no head gasket leak, yet.

wwxx

 

wwxx:The way we use to do it a hundred years ago, on OHV engines, was to use your feeler gauge for clearance and twist the push rod with your fingers, to notice exactly when the cam profile changes...

Back a half century, I worked on my dads 390. The pushrods would spin and stop, spin and stop. You had to run at a real slooooooow idle to see it, but as the lifter ramp took up the .00xxx clearance a hydraulic lifter allowed, it would stop spinning on the edge of the cam lobe. (cam lobes being ground at a very slight angle from being 90 to the tappet) Same information, but being done by the machine itself.
Some pushrods didn't spin. (sad face) They were on the cam lobes that were worn too much. The only solution was to keep driving, or replace the cam.
Back earlier, SAE made hard-bound manuals of their proceedings, from the early 1950's, which I read, not totally cover-to-cover, but a lot. The Packard and Cadillac 'new' OHV engines, with 'Hi-Compression", (maybe 8:1) had problems with the base of the lifter wearing the cam lobe edges and putting a hollow into the bottom of the lifter. From very old memory, the addition of Zn to the oil allowed for good service life.
Yeah, off topic, but not to this post, I think.
tom