T head engine by Brian

[J Tiers]

I'd rather collect with a baseball bat, or maybe a hammer.

[brian Rupnow]

My second flywheel arrived today. As soon as it came, I grabbed it and ran down to my lathe and machined it. It's a beautiful thing!!!--Still needs a keyway and grub-screws, but maybe tomorrow-----

[The Artful Bodger]

That surely is the cherry on the top of the cake!😍

[Toolguy]

Looks really nice, Brian. Can't wait to see it run! That one ought to have some torque with 2 flywheels.

[aostling]

Looks really nice, Brian. Can't wait to see it run! That one ought to have some torque with 2 flywheels.

I agree it ought to have impressive torque, but not because of the flywheel inertia. Average (mean) torque is equal to the product of BMEP (brake mean effective pressure) and displacement. BMEP will vary with load and speed.

[nickel-city-fab]

I agree it ought to have impressive torque, but not because of the flywheel inertia. Average (mean) torque is equal to the product of BMEP (brake mean effective pressure) and displacement. BMEP will vary with load and speed.

I'm learning something here -- I thought it varied with the stroke length?? (which I suppose could also be called the mean piston speed). I dunno, I would have to look it up ??

[aostling]

I'm learning something here -- I thought it varied with the stroke length??

That was the "word on the street" growing up. A longer stroke gives a longer moment-arm (at 90 degrees) so the peak torque during one revolution may be higher. But average torque depends only on the BMEP (for an engine of fixed displacement). You will notice that the units come out right: multiplying lb/ft2 (pressure) by ft3 (displacement) gives ft-lb (torque).

What makes for a higher BMEP? More energy released by the combustion. This is affected by air-to-fuel ratio, compression ratio, and (I suppose) ring sealing. I don't pretend to know then all.

[J Tiers]

The missing element is rpm.

The point in the rpm range where it occurs can be different. If you have a long stroke engine, it will generally have it's torque lower in the rpm range than a short stroke engine.

I had an S10 and a Volvo 240. Similar "power" in each. But the Volvo was significantly longer stroke than the S10. The 240 would "lug out", but the S10 would not. The 240 simply had it's torque at a lower rpm than the S10. For max power, the S10 had to really "scream" at a high rpm. (and at that RPM, the actual torque could be considerably lower for the same power).

Note that at similar power, the torque numbers will be different... the peak and average torque for the same power MUST be larger for a lower rpm engine, if the power is similar.

You need to look at what is being held the same in the example. Is it TORQUE that is being held the same? Or is it POWER? You will get different results depending.... It can get confusing.

[Willy]

Torque is what does the work, power is how fast that work gets done.
You want more of either in a given displacement size engine, the answer is simple even if the execution is not, burn more fuel.

Brian has been burning the midnight oil and look how much he gets done!

[brian Rupnow]

This is the part where I never know what is going to happen next. The second flywheel has been keyseated, grub-screwed and installed. I have had some engines start right up at this point, amazing and delighting me. I have had engines that ran, but needed considerable tweaking before they ran well. And I have had engines that wouldn't run at all, because something was out of adjustment, the valves leaked, because I had machined something wrong, or perhaps the small engine Gods were just messing with me.---Wish me luck!!!---Brian

[Toolguy]

Good Luck, Brian! Fingers crossed.

[brian Rupnow]

Okay---this one isn't going to take right off and surprise me. Fuel is getting ignited, cylinder is getting warm from firing. I'm not feeling a lot of compression here. The old "oil down the sparkplug hole" trick isn't bringing the compression up any, so this infers that the rings are doing their sealing alright. I will check again to make sure that there is daylight between the valve stem and the lifter when the lifter isn't up on the cam. (this will hold the valve open and no compression will be developed.) Since it does seem to be firing more or less consistently when driven by my electric drill, I will now put an electric motor to driving it, and see if the valves will seal up from the pressure created by the engines firing. if it wasn't firing at all, I wouldn't do this.

[brian Rupnow]

It seems that I have a leaking exhaust valve. Rather than screw around with everything bolted to the engine, I have made a "dummy cylinder" to bolt the cylinder head to. It is an exact copy of the cylinder, but without the center hole for the piston. First thing to check is whether the valve can be rotated into a position that doesn't leak. That technically shouldn't happen, but it sometimes does. Without changing anything on this set up, I can seal the leaking exhaust with my thumb and thus check the intake valve for leaking. I know that I used this same piece of equipment with the "blow yer guts out" test to see if the valves were leaking or not. They didn't seem to be then, but everything gets handled a great deal between that test and when the engine is finished. Today I will test things at 40 psi.

[brian Rupnow]

Compression has improved. Engine is now firing regularly along with power drill as I attempt to get it to take off and run on it's own. Cylinder is getting hot from firing. I am now going to take my degree wheel and check the ignition timing. The common knowledge out there is that four cycle engines should fire about 20 degrees before top dead center. Lots of puffs and snorts from the engine but haven't found the sweet spot yet.

[Sparky_NY]

Compression has improved. Engine is now firing regularly along with power drill as I attempt to get it to take off and run on it's own. Cylinder is getting hot from firing. I am now going to take my degree wheel and check the ignition timing. The common knowledge out there is that four cycle engines should fire about 20 degrees before top dead center. Lots of puffs and snorts from the engine but haven't found the sweet spot yet.

20 degrees before top dead center sounds like a lot of advance for a low rpm engine like this. I would expect less than half that amount. For example, I looked up a old Ford 4cyl industrial engine, max torque is at 1600rpm, max HP at 2400 RPM, the cranking ignition timing spec is right at TDC, zero degrees !


What does the compression feel like spinning the engine over by hand with the flywheel?