T head engine by Brian

[brian Rupnow]

No joy today. Very, very close, but no engine running on it's own. I'm having some kind of compression issue, and I think it is in the valves. Tomorrow I will reset the valve timing with my degree wheel, but my gut is saying it's a valve sealing issue.

[brian Rupnow]

No work on the engine today. Too busy playing with new bandsaw.

[brian Rupnow]

The valve timing was initially set using measurements from the top of the cylinder down to the top of the piston, taken from my 3D model when the crankshaft was positioned at the correct number of degrees before top or bottom dead center. I will certainly check the valve timing again with a degree wheel just to be absolutely sure of it.

[Sparky_NY]

To add to my previous response questioning the stated 20 degrees BTDC ignition timing, I looked up your typical Chevy V8 and they are spec'd at around 5 degrees depending on the engine. That 20 degrees the new engine is set at seems wildly advanced, I would expect it to be hard to start IF it would start at all.

https://itstillruns.com/timing-specs...k-7785189.html

[brian Rupnow]

Sparky--I arrived at 20 degrees before tdc by googling "Ignition Timing for 4 Cycle engines". Two or three different sites called for 20 degrees. I have some good tech manuals upstairs and I will take a closer look at them tonight.

[Sparky_NY]

Sparky--I arrived at 20 degrees before tdc by googling "Ignition Timing for 4 Cycle engines". Two or three different sites called for 20 degrees. I have some good tech manuals upstairs and I will take a closer look at them tonight.

I bet that number is at full advance (for engines with a advance mechanism) and for engines that rev quite a bit higher than yours do. Static timing would be much lower to provide good starting and low rpm performance (ie the chevy specs I linked). In your case, somewhere around 2-4 degrees should provide good starting but might hinder reving up well, I would guess something in the area of 5-8 would be a good compromise and starting point.

I am sure you remember some of the antique cars that had ignition timing right on the steering column, you backed it way down to start then raised it a bit after it was running. Good starting requires very little advance, sometimes none (right at TDC)

It would be a pretty simple test to back it down to 3-5 degrees and see if that beast will fire up.

[Jim Stewart]

I think Sparky has the answer. I've messed with lots of smallish engines (bikes) and lots of small displacement sports cars.

Starting advance was usually around 5 btdc and higher revs were around 20.

-js

[aostling]

Sparky--I arrived at 20 degrees before tdc by googling "Ignition Timing for 4 Cycle engines". Two or three different sites called for 20 degrees. I have some good tech manuals upstairs and I will take a closer look at them tonight.

Brian, you have a manual spark advance which you built for Thumper. Can you see if that works on T Head?

https://bbs.homeshopmachinist.net/fo...ore-i-c-engine

[J Tiers]

I think Sparky has the answer. I've messed with lots of smallish engines (bikes) and lots of small displacement sports cars.

Starting advance was usually around 5 btdc and higher revs were around 20.

-js

Yep. With old engines, it was common to retard the spark for starting, mostly to be as sure as possible that it would not kick back, but instead would start properly in the direction it is cranked.

[brian Rupnow]

I searched thru all of my tech books last night regarding "ignition timing" and they all hedge their bets, none giving an actual number but suggesting 0 to 30 degree range. Makes me crazy. Today I will reset it to 10 degrees before top dead center. Thanks guys.----Brian

[Richard P Wilson]

i used to work a lot with old low speed. single cylinder engines, and around 10 degrees would be about average, maybe less for starting

[brian Rupnow]

Okay Kiddies---It's showtime. Yesterday I had worked my way right into a snit trying to get this engine to run. I was almost at the point of making a new piston with a viton ring to get more compression. I decided that before changing anything, I would bring the engine in from my big garage and use a degree wheel to set the valve timing exactly "on spec" and to reset the ignition timing to about 12 degrees before top dead center.--I discovered that the grub screws in the gear which drives the exhaust valve had backed off and the exhaust valve timing was way out of whack. So, in the end, I really didn't change anything. The engine runs very well, and after playing with it a bit as "final tuning" I will reinstall the gear covers and clean everything up. If you would like to build this engine, I sell a complete plan set of engineering drawings, including detail drawings and assembly drawings for $25 Canadian funds, paid to Paypal to [email protected] Thank you to everybody who followed the build, and thank you for your posts and the information you have given me.---Brian Rupnow
https://www.youtube.com/watch?v=O_kE2aVUvWc

[Sparky_NY]

Brain, watch your video, something is going on at the base of the spark plug, either a bit of leakage or arcing, hard to tell but you can definitely see something happening there.

[mickeyf]

Definitely arcing, but hard to say exactly from where without a close up.

[brian Rupnow]

No, it isn't arcing. It is bubbling. It's leaking a bit of compression around the sparkplug. I have to put a better copper gasket under the plug.