Oddball engines and prototypes

[Jannem]

Plugged the numbers in where?
You may also want to take another look here, regarding your mean area: https://www.kiwibiker.co.nz/forums/s...post1131055378

Come to think of it, maybe a more fundamental explanation may be in order:

Blowdown angle.area

Blowdown angle.area is not simply the total blowdown area multiplied by the total blowdown angle. It is the sum of a lot of small area steps, multiplied by the time during which each of these steps is open.

For example, let us assume that the exhaust port is a simple rectangle, 40 mm wide, that it opens 1 mm further for each degree of crankshaft rotation, and that the total blowdown angle from the point where the exhaust port is beginning to open till the point were the transfer ports are beginning to open, is 30°.
Then the first degree of exhaust opening will open an area of 40 mm x 1 mm = 40 mm², and this area will be open during the whole 30° of blowdown period. That first area thus has an angle.area of 30° x 40 mm² = 1200°mm².

When the crankshaft turns 1 degree further, an additional area of 40 mm² is opened. This second area will be open during 29°, so its angle.area is 29° x 40 mm² = 1160°mm².

Repeat this calculation for each crank degree until the end of the blowdown phase, and add all the angle.area values; that will give you the total blowdown angle.area.

In reality this calculation is complicated by the fact that not every degree of crank angle gives the same port height difference, and even more complicated by the fact that the exhaust port is not a simple rectangle. But you will understand the principle of angle.area.
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Transfer angle.area

Let us assume a transfer port with a timing of 130°.
When you turn the crank 1º past Transfer Open, a certain area of port, say A1, will be exposed. I don't know or care what that area is, that's for you to measure.
That area of port A1 will be open for 130º. The angle.area for this area A1 is = 130 x A1.
Turn the crank another 1º and an additional area of port, A2, will be opened.
This additional area A2 will be open for 128º. The angle.area for this area is = 128 x A2.
The next degree of crank rotation will open Area A3 which will be open for 126º and its angle.area will be 126 x A3.
Keep going like this until BDC, then add up all the angle.areas you have calculated.
The total is the angle.area for that transfer port.

Thank You Frits, this clears it up a lot.

As for your question where I'm plugging the values, I've built up a spreadsheet with measured port and cylinder values and I'm using it to test impact of different modifications in timings and areas. Getting this nailed down is the last step to be able to have a solid target to aim for (without investing to a simulator, which is not in the cards right now).

I appreciate all the help I've got from you very much. Actually, we do, as this is a joint project with my son.

-Janne

[WilDun]

Sorry, we are talking on two different subjects here, but I guess that's the way forums work!

Just to say that I found a good picture of the Midget "Offy" engine:-
Not a head stud in sight!

[Grumph]

Sorry, we are talking on two different subjects here, but I guess that's the way forums work!

Just to say that I found a good picture of the Midget "Offy" engine:-
Not a head stud in sight!

Yep, all top 1930's technology. Head and barrel in one casting, bearings for the crank on bolt-in diaphragms in the crankcase, hollow rods...

And it worked well too. Competitive right up to the 70's. And they sound bloody good on full noise too.

As an aside, a mate at Auto Restorations in ChCh was doing an Alfa P3 GP engine which is the same integral head layout last time I was in there. He showed me the OE valve guides which slipped in and were retained by the springs. Had to be like that to fit big valves up the bore and angled into the port...
He'd discovered that guides 1mm shorter would allow fitting the valves while the guides were in the head so had made up a set of shorter guides which were pressed in. Better heat transfer and valve life. He also built the Britten engines...

[Frits Overmars]

Thank You Frits, this clears it up a lot. As for your question where I'm plugging the values, I've built up a spreadsheet with measured port and cylinder values and I'm using it to test impact of different modifications in timings and areas. Getting this nailed down is the last step to be able to have a solid target to aim for (without investing to a simulator, which is not in the cards right now).
I appreciate all the help I've got from you very much. Actually, we do, as this is a joint project with my son.

My pleasure Janne

[guyhockley]

Yep, all top 1930's technology. Head and barrel in one casting, bearings for the crank on bolt-in diaphragms in the crankcase, hollow rods...

And it worked well too. Competitive right up to the 70's. And they sound bloody good on full noise too.

As an aside, a mate at Auto Restorations in ChCh was doing an Alfa P3 GP engine which is the same integral head layout last time I was in there. He showed me the OE valve guides which slipped in and were retained by the springs. Had to be like that to fit big valves up the bore and angled into the port...
He'd discovered that guides 1mm shorter would allow fitting the valves while the guides were in the head so had made up a set of shorter guides which were pressed in. Better heat transfer and valve life. He also built the Britten engines...

More modern iteration of the no head gasket.

[guyhockley]

Sorry, we are talking on two different subjects here, but I guess that's the way forums work!

Just to say that I found a good picture of the Midget "Offy" engine:-
Not a head stud in sight!

and the bolt on water jacket could be relevant to someone on here...

[WilDun]

More modern iteration of the no head gasket.

Plenty of modern "complete" head/barrel examples in the two stroke scene, especially in chainsaws and the like. Not great for buckets though to get the squish clearances right! but then knowing our "bucketeers" they would no doubt, get round that one with head inserts!

I'm surprised that this isn't used more in production competition engines today (both two and four stroke), considering the fact that head gaskets and high compression can cause countless problems which will spoil your day, also the re-machining of a head is no simple job! (can only be done so many times as well, then it's a new head!).
The accurate machine tools we have in factories today could easily put the squish clearance problems to bed.

Pretty sure that the Moto Guzzi V8 used the "one piece" head/barrel as well, it had screwed in liners too, (with threads up top and a taper seal above them).

I reckon the Offenhauser was a good solid design, still a very strong possibility today!
Grumph's (or whoever's) idea of simplifying valve maintenance could then become the standard way of doing the valves in situ.

[Grumph]

Can't see the modern 4T production engine going back to a one piece barrel and head sorry Will. The current thinking is that block/crankcase stiffness is paramount to keep it reliable at higher revs. Plus the sheer complexity of modern 4v head castings makes it bloody hard to do it all in one piece.
Yes, things like the Hart very high boost race engines may still appear. It's even possible that the F1 engines using HCCI are done like this but it's not common now. What is becoming more common in bikes is amalgamating the crankcase and barrel as is car practice. Weight reduction and improved stiffness again.

I can quote an extreme case - Delage straight eight GP engine, Auto Restorations again. They did a "better" stiffer crank for it. Around 3 feet long - just under a meter Frits - and within a half hours running, the separate block cracked. The OE copy crank they didn't like allowed things to flex and move around quite happily.

[WilDun]

Can't see the modern 4T production engine going back to a one piece barrel and head sorry Will.........

Yes, I do understand that there would be a very good reason for not doing it that way - otherwise they would be doing it - I just I didn't know the reason! - it almost always involves cold hard cash!
Pity to see some gems disappear just because of that.

It's even possible that the F1 engines using HCCI are done like this but it's not common now.

Is HCCI actually being used in F1 now?

I can quote an extreme case - Delage straight eight GP engine, Auto Restorations again. They did a "better" stiffer crank for it. Around 3 feet long - just under a meter Frits - and within a half hours running, the separate block cracked. The OE copy crank they didn't like allowed things to flex and move around quite happily.

I believe that when the first Matchless parallel twins (500cc models) came out there were some serious crankcase cracking problems (or was it just broken cranks?) with their super stiff 3 bearing setup (unlike the 2 bearing cranks in the Triumph, Norton and BSA twins ).
Then in the Norton Commando, the big 750/850 twins were just let loose to do whatever they wanted to do in just about every conceivable way (including the engine mounts!). - They obviously hadn't heard of Dr Lanchester's ideas on balance, or just ignored them!

[Pursang]

Sorry I haven't been around for the Offy stuff (a topic I really like too).

I had to send an old friend off this week, his family asked me to write and present his eulogy.

Don Newell was a pioneer of Bultaco in Australia, and a racer to his core.
He was still competing in Classic MX at 83+ years.

Pdf copy here, if you're interested.


Cheers, Daryl

[Pursang]

Don in Action, around 2 years ago, (Blue Bultaco) First to the first corner...again.

https://www.facebook.com/guy.westerm...7458104610988/

Cheers, Daryl

[WilDun]

A very nice Eulogy Daryl and very informative as well! - I feel now that I actually knew the guy!

[pete376403]

I believe that when the first Matchless parallel twins (500cc models) came out there were some serious crankcase cracking problems (or was it just broken cranks?) with their super stiff 3 bearing setup (unlike the 2 bearing cranks in the Triumph, Norton and BSA twins ).
Then in the Norton Commando, the big 750/850 twins were just let loose to do whatever they wanted to do in just about every conceivable way (including the engine mounts!). - They obviously hadn't heard of Dr Lanchester's ideas on balance, or just ignored them!

Commando cranks used to flex to the extent that the main bearing rollers were running on their end edges, rather than the whole width of the roller. "Superblend" rollers were used to mitigate this - the cranks still flexed, but the bearing lived (longer)

[Pursang]

A very nice Eulogy Daryl and very informative as well! - I feel now that I actually knew the guy!

Thanks for that. It's pretty hard to compress such a full life into a couple of minutes.

cheers, Daryl.

[WilDun]

Commando cranks used to flex to the extent that the main bearing rollers were running on their end edges, rather than the whole width of the roller. "Superblend" rollers were used to mitigate this - the cranks still flexed, but the bearing lived (longer)

"Superblend"? - Are they also called barrel rollers? - guess they were a bit of a compromise, but they did work.
Had a ride on a "Combat" many years ago - impressive amount of torque!