??? In Regards To Quench & Compression

[GPH85]

I got bored today and decided since I've already stolen a coil off of it "to fix my C9", I would experiment on it The saw that this is in regards to is a Homelite C5 with C7/C9 crank. It already has 155 - 160 lbs compression. I was wondering what harm would there be in shaving the cylinder seat some. I measured the quench and discovered that even with the C5 piston "has .022 thousandths higher dome than the C7 piston", it still has .122" quench with no gasket, SO your looking at roughly .140" with a .020" gasket if you take into consideration the effect of gasket squish during tightening (I was figuring right around .002" with this thin of a gasket). Now I know the pro's on here say that you should have right around .020" - .030" quench, so I was wondering what everyone's thoughts on having right around .100" milled off was??? I know this is a whole whole lot considering it's 1/3 of the seat material or seat base of the cylinder, so any thoughts on a smaller milling amount to where I could still use regular pump gas??? This saw has already benefited quite a bit just by having the higher dome piston, so I was figuring why not up the compression a touch more...

I was also going to lower and slightly angle the exhaust port and do a very very minor change to the intake ports "not a whole lot you can do with this design". Any thoughts or comments on this?

I really don't see how these engines develop the 150 lbs compression that they do with this much quench, but I don't want to get over 200lbs compression either.

What kind of compression readings are some of you getting off of your modified saws and what type of fuel are you using?

Thanks for any helpful information you may have in regards to this matter.
Greg

(SIDE NOTE) For anyone who is waiting on the postings of my C9 with gear drive, it will be late Monday or maybe even late Tuesday before I can post them... The photo shop at Wally World is having printer issues, so I can't have my pics put on a cd, so I can upload them, until they get it fixed

 

[ol'homey]

What's the highest compression pressure that will allow you to pull start the engine without breaking your arm on an engine without a decompression valve?
I know the larger the cc's the lower the max. pressure will be before high cranking torque becomes a problem. I'd hate to spend $ modifying an old Homie only to find out I couldn't crank it without tearing my arm off. Can anybody shed more light on the subject?

 

[ShoerFast]

Cranking pressure and actual running cylinder volume are 2 different things, so how much compression, or correctly named compression ratio you can get away with will vary from saw to saw, and combustion chamber design.

In general, your adjusting the running pressure that you want to compact the air-fuel charge that will affect the running cylinder pressures and flame front, go too high and your needing higher octane to control the burn rate pressures. The old school trick was to raise the CR , run a shade cooler plug and back the timing off a little if you still wanted to run regular gas.

What ever you set the saw up to run at, remember that as it builds hours, the carbon that builds up in the combustion chamber will also raise your CR , we all have experience with how well something ran, just before it gave up the ghost.

Understand, my experience is with mostly 4-smokers, basic rules of combustion are the same, but there is a lot of difference in opinion on what makes a hot saw.

 

[GPH85]

After further inspection of my exhaust port and piston alignment "with no gasket", I think I'm just going to try a have .020" thousandths removed and see what it does after all .022" has already made a reasonably big difference... If I removed any more, I would have to either completely move the exhaust port up (don't have the time, a tig welder or just time to do this "did I mention time ", plus this would defeat what is trying to be gained) or modify the piston somehow to allow for a lower exhaust port position "compared to the piston position at bdc", which would further defeat what is trying to be gained and possibly ruin the flame propagation on top of all of this

The only reason I'm experimenting on this one is because it doesn't interfear with my collection at present time, but if it works, I may possibly do the same to my other C-Series saws before having all of the saws restored "to boost torque, power and combustion properties such as flame propagation a small bit".

I already knew about the arm thing, especially since 162lbs compression can be hard at times, which is why I stated nothing above 200lbs compression "if I had gone to extreme milling amounts". I'm really looking for something in the 170 - 180 range, but I know if I only shave it another .020", it may only up the compression another 5 or so lbs which would put it in the 160 "constant" - 165 lbs compression range, which hopefully would be right around perfect

I've never changed a spark plug heat range in an engine I've built to get around using one fuel to another... I've only done it to get the fuel burn "color" right where I wanted it (a nice dark to light golden brown) and to which ever plug did the best in the engine I had built (i.e. power / fuel mileage). I would also gap these plugs to acquire this "perfect" color. Example being my dodge V6 (3.9l magnum 99') switched to AP3923's (I know there are better plugs out there, but these are cheap for experimenting, right) gapped to .058" (using msd blaster coil - capable of going to .060", but my heat range wanted was right in the .056" - .059" gap range). .055" was too dark a brown and .060" was too hot or non existing brown color... With my modded engine and this plug setup, the best recorded fuel mileage was 27mpg at a constant 60mph through the mountains here "no downshifting on hill sides" for a roughly 50-60 mile drive. It would usually range in the 24-25 mpg range depending on my driving habits

Any thoughts on the .020" shave or the best way to work the ports, if any???
Thanks Again,
Greg

 

[ol'homey]

How about putting it together without a gasket and see what happens with the compression? I'm not saying to run it, just do a compression test and see what you get. Then you'll know what effect taking off the thickness of the squished gasket (.015?) has on the pressure. Let's say the pressure increases 10 lb without the gasket, and you want to increase it by 30 lb with the gasket on. You would have to take .045 off the cylinder base. Let us know the before and after pressures if you try it without a gasket.
Lee

 

[GPH85]

OOOPPPPss, I already machined down the surface .030"... I know depending on temp outside, it seams, that the compression before was 155lbs - 160lbs... I believe you know this for yourself after moddifying your saw with the C5 piston... As for after words compression, I'll have to get back with you on that one. I'm also in the process of altering both the intake and exhaust ports a small amount. If I can, I will try to get some pics posted in this weeks time span That is as long as no one has any more film processing problems. Called today and the CD I'm having made up, so I can post the pics of my C9 with gear drive, still hasn't been developed or made :bang: Said it should be tomorrow, but we all know how that goes :bang:

I went with the .030" because after further inspection the original place I was measuring gasket thickness at, was thinner for some reason. The rest of the gasket material seams to be .030" on average give or take a couple thous... I'll just make sure to cut out the thinner material and use the "consistently" thicker stuff

I'll be sure to let you know how it turns out "good and bad"...
Greg

 

[1953greg]

an alternative to complete gasket removal is cutting one out of a paper sack. bout .005" thick and probably squishes to 2-3thou. still use a small amount sealant rubbed on paper seal between fingers. works for me

 

[ol'homey]

Wish I had thought of that before I put my C72 back together. Do you use an ordinary brown paper grocery bag with a non hardening sealant like permatex 2B? Have you ever tried just sealant with no gasket?
If so what sealant did you use and how did it work?

 

[GPH85]

Verdict isn't completely in yet "I just did basic enough assembly to get a reading", but so far so good...

Afterwords Compression Reading = 182lbs compression :biggrinbounce2: (this is with reed / carb and rewind assembly on "basic" engine "no handle and everything else" - I used minor assembly lube, so as it wouldn't throw the reading off)

Now I just have to tear the carb and rewind ass. back off and assemble it right and stick her in some wood and see how she does... I got the pictures of the gear drive today and will try to load them LATE tonight, but I already tried loading one and it didn't want to load... Well see I guess Not guaranteeing anything though...

I just hope it runs really good and on regular gas

Greg

 

[GPH85]

WELL, I've come to a couple of conclusions...

First Off - The bar and chain combo I picked to use on the saw was a mistake... Kept wanting to cut every which way and was throwing out "little" saw dust type shavings. It was almost like it was in a bind, when it shouldn't have been.

2nd Off - Evidently this particular saw has a 3 shoe clutch on it and not a 6 shoe, like I've put on all of my other saws or at least I sure hope it's got a 3 shoe. I guess the fact that it was originally an experimental saw was the reason why I didn't put the 6 shoe setup on it (put the 6 shoe setups that I had on the saws I knew I would be using the most?). I should really right down what I've done to each saw, so I can keep track of them. At least I hope it doesn't have a 6 shoe, because if it does, I'm in trouble... The saw would only lug to about 7/8 to 3/4 percent of full throttle. If the chain hung or anything the saw wouldn't lug down, it would just "smoke" or slip the clutch. It seemed to stay revved up no matter what...

This thing is great Of course I didn't get to really try it out, because of the clutch and chain dilemma and the fact that it was just about dark when I finally got it back together and a minor carb tuning done, but I did get to see how it was going to perform in general. I was also surprised in how fast it started up. Only took 6 pulls with no fuel in carb or fuel line... I was even using regular grade gas "old at that" and it didn't seam to "ping" any... Revved up extremely nicely / I had the max rpms set WAY up there for these saws and as stated it didn't seam to want to lug down any much under load...

This thing could really benefit from a larger carb off of an XP or 1050 or some saw of this size...

I'm "so far" really happy with it...

I'll have to put my 30 inch bar on it, after I check the clutch out, and see how it handles it

 

[GPH85]

OL'Homey, if you would rather use a sealant, here is the best sealant I've ever used... Runs about $10 or $12 for a 100g bottle... HYLOMAR made by Valco Cincinnati... It has Never Hardens (this stuff unlike the other stuff that advertises the same thing, really never does harden - stays kinda like already chewed chewing gum) / Impervious To Most Fuels / Gasket Maker , Thread Sealant / Temp Range -60F - +600F / Superior as Gasket Dressing

I use the same stuff on any truck or auto engines I build. Never had any leaks even after years of use. It was suppose to be for or rather used on jet engines "advertisement when I bought it", but I don't know of anywhere on a jet engine that needs sealing like this???

I bought it through Hughesengines.com, but it has a phone number and address on the back (where it's made perhaps) - 411 Circle Freeway Dr / Cincinnati, Ohio 45246 / 513-874-6550 ... I'm sure you could buy it a whole lot cheaper through the company then through hughes engines...

I have yet to change out the clutch and bar, but will do shortly to let you know how the "overall" performance of the saw is
Greg

 

[GPH85]

This thing has more power and torque than my C9 or C91 (of course it should, if is has more than one, have more than both considering they have the same engine) I love this thing... I wound up putting the same size bar as I had just had on it "18 inch", back on it, but this time I used .404" pitch Full Chisel chain that had the guides filed down on (So as it would really bite in). This way I didn't have to worry about switching bars around so much - This saw may have more power, but I would rather use my C91 with the 30" bar to work with and save this one to play with

I set this thing down in some 18" popular and it just dropped right through... Set it in some 18" walnut, dropped right through... Started digging in the dogs (bumper spikes) and forcing the cut "would hang if bar was pinched on any - was kinda working in a wood pile mess", but still would really drop through it... Really throws out the chippings too with the guides filed down on the chain I cut so much with it, I actually ran it out of fuel... Not good I know, but I was having fun playing and it cut great even till the last drop, it seemed...

Oh the clutch it had on it was the 3 shoe, I put a nearly new 6 shoe on it, but it still stays at half to three quater throttle even under load

I'll try to get some pics posted of all the modifications I did to it, incase anyone out there is willing to try or just wants to copy them... That is if the pics turn out good - I really wish I had a digital camera

The only regret I have, after thinking about it, is that I retarded both intake and exhaust port timing. I didn't mind retarding the exhaust so much, but I would have liked to of raised or advanced the intake ports a little... NOT much granted, but just enough to smooth out the transitions into the cylinder :biggrinbounce2:

Greg

 

[ol'homey]

Ok, now your next project should you choose to accept it is to get an idea of how much HP this thing is putting out. Assuming you don't know somebody near by with a chain saw dyno I've got an idea:
We know HP= torque(ft-lb)(RPM)/5252
All you need is a tach to measure the rpm and a way to connect the sprocket to a cheap deflection beam torque wrench and you're in business. Maybe you could weld a big nut onto a worn out sprocket. The nut would have to have an id big enough so you can put the nut back on the crank to hold the sprocket on. It should also be as wide as possible so when you put a socket on it it won't fall off under load. Maybe put the torque wrench in a vise or jig so it can't move around and come off under load. Use a video camera to record the reading on the torque wrench as it would be too risky to have somebody's head that close to the wrench under load. What kind of torque are we talking about anyway? T= (HP)(5252)/RPM Let's say you put the 3 shoe clutch back on to allow the saw to get up closer to the rpm at which max HP occurs and your saw makes 6 HP at 7000 rpm. T= 6*5252/7000= 4.5 ft-lb
That's not much is it! Better switch to a wrench that reads in in-lbs. Wait I've got a better idea. Instead of welding a nut onto the sprocket weld say a 3' long piece of rebar. Since it will only have about 4.5 ft-lb of torque on it it doesn't have to be super strong. Then set the end of the bar on a postal scale and tare the scale so it reads zero. At 4.5 ft-lb the scale should read 1.5 lb. Let us know if you decide to try it. I'll probably give it a try myself!

 

[GPH85]

For some reason, that sounds extremely painful :sword: Really, you can't get an accurate torque reading without direct hookup to the engine "as in an engine dyno"... It is interesting though and I would try it, honestly just to see what came out, if I had a sliding "old fashion" torque wrench... WAIT, I do have a "dial type" torque wrench that reads in inlbs... What's the conversion of inlbs to ftlbs. Every 12inlbs = 1ftlb of torque??? It goes up to 75inlbs so what would that be / 6.25ftlbs??? You know what else, I've got a 6 tooth 1/2"pitch sprocket "brand new never used and don't guess it ever will be", that a 1&1/2" socket fits perfectly around or rather on... Sprocket has a nice hex spacing pattern BUT, I'm afraid I'm going to max out and break my $264 Snap-On torque wrench, but then again on the other hand the Snap-On torque wrench does have a lifetime warranty, right

As for the clutch shoe setup, with the way this thing stays in the high rpm band, even under max load, I don't think I will need to change back to the 3 shoe for this test It will more than likely have to wait until later this weekend sometime We started back to "work" today and will continue cutting down trees all through Saturday, more than likely... Then I have a saw that my cousin dropped off for me to fix that I will be working of either late Saturday, or early - not really sure as of now, and will more than likely still be working on till Sunday late Although, I only have to fix a kill switch issue and a plug boot issue, then probably do a minor tune up on "already fixed the broke rewind issue", so I may get it done Saturday... Who knows...

I'm still afraid it's going to max out and break my gauge, because I know it's more than likely got more torque than a measly 6.25ftlbs "like previously stated, this thing fell right through anything I would throw at it, even though it was mostly soft wood", but I'll see what happens...

Greg

 

[GPH85]

Oh, I don't have a tach BUT my mutimeter has an rpm read out on it :biggrinbounce2: SO as long as it's accurate, I guess I could still get the numbers, right? Only it would involve running the saw with the complete flywheel and rewind assembly removed "so as I could hook up the inductive hook up around the plug wire"... I don't have to worry about filming the readout, this torque wrench has a needle that will move and stay where the other needle maxes out

Well, we'll see what happens I guess...

 

[ol'homey]

Most small engine dynos are just a hydraulic pump coupled to the engine with a belt and pulley. You open or close the valve controlling the flow of fluid to vary the load. The pump body is mounted so it can rotate and the attached arm and spring scale is calibrated to give you the torque. All you are doing here is using your clutch to provide the load and attaching your load arm directly to it. You can then use a spring scale or postal scale etc. at the end of the arm to measure lbs and then multiply by the length of the arm to get ft-lbs. The only draw back to this method is that you can't vary the load and rpm like you can with the hydraulic pump. All you can do is measure the torque at whatever rpm your clutch allows the engine to rev to. IOW if the saw only makes it to 4k rpm with the 6 shoe clutch you will be reading less torque and less HP than with the 3 shoe clutch that might let it go to 6k.

 

[ol'homey]

The Stihl MS880 is rated at 8.5 HP at I think 9500 rpm.
T= HP*5252/rpm = 8.5*5252/9500= 4.7 ft-lb

Unless you believe your saw has a lot more torque than the largest saw Stihl makes you don't need to worry about your saw breaking your torque wrench. Notice that the higher the rpm that any given HP is made, the lower the torque.

 

[GPH85]

I know how a dyno works I ran both a chassis and engine dyno at the college I went to BUT an engine dyno does one thing that I learned very quickly that this does not... An engine dyno won't start loading the engine until you get it up in the rpm's...

This setup absolutely won't let you get the rpm's up to get an accurate reading... It doesn't matter whether your running a 6 shoe or a 3 shoe and the test I ran got 3 different numbers and I know when you make pulls that the numbers should be or rather will be different, but I know that these numbers are way off of what the saw actually has... I know this because the C9 should have 5 - 6hp, right, and this saw will run circles around it, but I was getting 4.8hp, 3hp and 3.4hp with torque readings of 4.6ftlbs, 3.75ftlbs and 4ftlbs...

I know the torque numbers are fairly correct (you can't go wrong with a turning torque measuring torque wrench, right) but the hp numbers are off... This is probably because I never could get a constant good rpm reading with the setup I was using. It would jump through 2000 rpm bands, all over the place and is more than likely my hp numbers are way, way off... After all, I used the general area that it was registering in for my rpm numbers...

I also noticed that my first two pulls were the best (I did 6 with all sorts of rpm numbers). They are the one's where I got around the 4.6ftlb readings... They were also the two pulls where I used the 6 shoe clutch, the other 4 were with the 3 shoe... All of the pulls after this weren't all that great... I think this is because I put the bad coil that was on my C9, on this saw, so the hotter it got, the weaker the output of the spark became = less efficiency... Plus as an engine gets hot the compression starts to drop off a little, which would again have some effect on it...

I don't know... What do you think. If I ever get a better tach of some sort, I'll do this again and see what I come up with. Until then, all I can get are the torque numbers on my saws, which is nice, but they won't be that accurate, because you can't get the rpm's up that much Might could put some oil on the clutch and see what happens, but I would rather find a small engine dyno and run it on it...

On the up side for anyone who ever just wants to get torque readings, this was one extremely easy test... Didn't have to clamp the saw down or anything, just tied the wrench on and ran it... This is, however, extremely hard on clutches

 

[GPH85]

The very, very first pull I got 65inlbs = 5.4ftlbs torque, but I figured I should post the least reading of the two or each group of two pulls... This way it would be more accurate, I figured... This was one of the first two pulls with the 6 shoe clutch...

If this helps any with numbers

 

[ol'homey]

I was looking at my clutch spider and noticed you can run it with just two shoes across from each other. That's what i would do to get the rpms up. If that's not enough put some grease on the shoes and drum. Still not enough, cut some grooves in the shoes to reduce the contact area with the drum. Of course you would only do this with shoes and sprocket out of your junk box. Get the saw up to operating temp before you put on the wrench. When you take the reading just snap the throttle open long enough to get a stable rpm reading and then shut it off. The clutch will be dissipating 746W/HP. So if your saw is making 6 HP the clutch will be dissipating 6*746= 4476W which will cause the clutch to quickly start smoking just like it would if the bar was pinched in a cut and you held the throttle wide open for longer than a second. The first thing you need to do though is find a tach that will give you an accurate reading. I use a Stihl tiny tach which is good to 100 rpm and takes maybe 1 sec for me to see a stable full throttle rpm reading. You can test your tach by just seeing what it's doing at idle and at full throttle with no load. If the reading is jumping all over the place it's not going to work.
If you do spend a bunch of $ on a dyno you're still going to need an accurate tach to get meaningful results, so you might as well get one now.