ESE's works engine tuner

[F5 Dave]

Can't help you there but your gudgeon pin looks dreadful. Hope that's an old scrap one.

[TZ350]

Can't help you there but your gudgeon pin looks dreadful. Hope that's an old scrap one.

You are right. It is a re used one. looks much worse in the photo than real life. Camera picks up all the little discolorations.

[wobbly]

Dead correct , for a race engine 58% is proven technology.

[husaberg]

You are right. It is a re used one. looks much worse in the photo than real life. Camera picks up all the little discolorations.

Out of interest, What is the balance factor now in its current mondo vibrating form?

[F5 Dave]

You are right. It is a re used one. looks much worse in the photo than real life. Camera picks up all the little discolorations.

I think you are flattering your camera. Looks like it was taken with a Nokia flip phone.

[TZ350]

Out of interest, What is the balance factor now in its current mondo vibrating form?

I did not bother to work it out. All I know for sure is that it vibrates really really bad at 9-10,000 rpm. When I looked into it I found the reciprocating weight side was notably heavier than the counter weight side.

P.S. Thanks for the link, read up on the 10,000 rpm 250 single and that they dynamically balanced the crank. I have seen car cranks done that way but how to make something home made to test a single crank looks challenging.

Lots of interesting reading here on bikes and adventure:- https://www.oldbikemag.com.au/

[TZ350]

I think you are flattering your camera. Looks like it was taken with a Nokia flip phone.

Yep you are probably right. I should dig around in the old tea chest again and see if I can find a better piston pin. I suppose you would be horrified to know it's the same place I found the little end and cir-clips.......

A great deal of this engine came out of a Cowshed and old wooden Tea chest.

[Frits Overmars]

.
F81M balance factor post 1.
Reciprocating weight is 372g

50% balance factor would be 186g.

Where is your con rod in that second picture? The weight of its small end should be part of the 186 g.
186 g plus the small end weight will give a notably higher balance factor (which in practice may not be a bad thing).

[Gradella23]

Where is your con rod in that second picture? The weight of its small end should be part of the 186 g.
186 g plus the small end weight will give a notably higher balance factor (which in practice may not be a bad thing).

Hello Frits, it's been an honour to read your posts on the various forums during the years.
Regarding the balance factor, i'd like to ask you which is, in your opinion, the best route to follow when manufacturing a crankshaft from scratch: once I know the alternating mass, and designed the crank webs according to the engine case... how should I continue? simmetric holes on each big end side? a simulation?

my engine also has its oem balance shaft (pic below): if I, for example, use the 58% balance factor Wobbly suggested on the crankshaft, is there a way to properly adjust the balance shaft factor? (other than trying i guess, but just to have a starting point). Tbh I've also read Jan Thiel saying that you must just get rid of cagiva type balance shaft, but there's always time to throw it away after testing

thanks in advance.

[Frits Overmars]

Hello Frits, it's been an honour to read your posts on the various forums during the years.
Regarding the balance factor, i'd like to ask you which is, in your opinion, the best route to follow when manufacturing a crankshaft from scratch: once I know the alternating mass, and designed the crank webs according to the engine case... how should I continue? simmetric holes on each big end side? a simulation?

my engine also has its oem balance shaft (pic below): if I, for example, use the 58% balance factor Wobbly suggested on the crankshaft, is there a way to properly adjust the balance shaft factor? (other than trying i guess, but just to have a starting point). Tbh I've also read Jan Thiel saying that you must just get rid of cagiva type balance shaft, but there's always time to throw it away after testing
thanks in advance.

Grazie Gradella.
A full description of how to manufacture a crankshaft would take more time than I have available. But I would strive for symmetry as much as possible.
You can also take a look at an Aprilia RSA125 crankshaft; not at the RSA250 crankshaft, because that is asymmetrically balanced.

For an engine with a balance shaft I would give the crankshaft a 50% balance factor en let the balance shaft take care of the other 50%.

The Cagiva balance shaft in your photo evokes memories. In Calusco d'Adda, where Jan Thiel and I lived for a while, we knew a Sport Production rider with a Cagiva Mito. According to the regulations you were not allowed to do anything to the engine but when I saw that balance shaft, I saw possibilities. It rotated at the bottom of the crankcase, submerged in gearbox oil, like a cream whipper. That must have cost power, so a cylindrical sleeve was fitted around it, smoothing its circumference. This brought 2 hp and no one ever thought of checking not only the cylinder but also the balance shaft.

[Vannik]

.

Attachment 352576 And a picture of my F81M's rotary valve compared to a standard unit for anyone interested in such things.

I am surprised no-one commented on this yet!

[pete376403]

I am surprised no-one commented on this yet!

Wish I had known that 50 years ago. I had a 72 F9 (Bighorn) 350 that did that twice. Once with the standard rotary valve, and once with the disc I had trimmed a bit off. Wear on the port was the least of the damage, the stainless bits made a real mess of the piston.

[TZ350]

I am surprised no-one commented on this yet!

I had rounded the edge's of the disk so that the port was completely opened/closed at the same instance in the hope that would improve the induction pulse. Wondered why the port edge was wearing. Thanks for the heads up.

[TZ350]

Where is your con rod in that second picture? The weight of its small end should be part of the 186 g.
186 g plus the small end weight will give a notably higher balance factor (which in practice may not be a bad thing).

Thanks for the heads up. I thought weighing the reciprocating mass and then hanging a percentage of its mass off the end of the conrod was the way to go. I will have to re visit how I am doing this.

[wobbly]

The best disc shape to help wear is to angle cut the closing side as per this Aprilia pic.
I tested every shape possible doing Hines 250 Rotax Superkart , and nothing made any more power than that - with the added bonus of less wear on the case.