The International Cessna 170 Association

The rear view mirror was a sure tip-off for me, that was no ordinary Vespa.

Dang, you guys just made my day!

Some motor porn along with a BL story!

More engine porn, so long ago I rebuilt this guy twice. A real education in patience and precision, it only comes into time (because of odd number of teeth on lay and vertical shaft gears) once every 16 revolutions and each combustion chamber volume is set using a graduated burette.

johneeb wrote:... each combustion chamber volume is set using a graduated burette.

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John, Forgive my ignorance. How was this volume changed? I assume the goal was to match each chamber volume with the others but why would one be different than the next?

OK, now it makes sense why we haven't heard from the 27% Scale 170 project for a long time.

Well, it's good to know you won't be getting bored anytime soon!

n2582d wrote:

johneeb wrote:... each combustion chamber volume is set using a graduated burette.

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John, Forgive my ignorance. How was this volume changed? I assume the goal was to match each chamber volume with the others but why would one be different than the next?

Gary,
The variable in volume are due to casting differences in both the heads and the pistons and also very hard to cut valve pockets exactly the same from one piston to the next. We did do Cosworth cylinder heads as Arish mentioned and still checked the volume with the engine assembled. On the Porsche the initial volume is adjusted by metal spacer rings below the cylinder skirt base and then fine adjustment by removing metal from the head.

Picture the (sad) day the car returned to Germany with its new owner!

Very interesting! I’m astounded by the technical talent so many of the members here have.

So if you’re milling the pistons to match valve pockets where do you remove metal to match piston weight? I imagine at the rpm these engines turn everything moving internally is matched weight-wise down to a fraction of a gram.

Aryana wrote:John that Porsche is beautiful. Must have been hard parting with it.

I still regret selling my humble little 912, and now the prices have skyrocketed.

Very hard, however it did allow me to build my 170. Wish I could have figured out a way to do both.

n2582d wrote:Very interesting! I’m astounded by the technical talent so many of the members here have.

So if you’re milling the pistons to match valve pockets where do you remove metal to match piston weight? I imagine at the rpm these engines turn everything moving internally is matched weight-wise down to a fraction of a gram.

Gary, with your experience you must have seen the inside of an engine that has been balanced, there will be belt sander impressions on both ends of the connecting rods and crankshaft counter weights and the under side of piston dome will have very shallow drill marks. All very important, especially when you want to turn up the RPM like the engines in Arash's bikes.

I wonder what the dynamic balance on this is?

Probably measured in ft-lb!

hilltop170 wrote:I wonder what the dynamic balance on this is?

Probably measured in ft-lb!

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At the typical 1800-2000 RPM it hardly makes a difference (especially when compared to the steel prop some of them twisted)

hilltop170 wrote:I wonder what the dynamic balance on this is?

Probably measured in ft-lb!

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Richard, do you put lights on that at Christmas time?

Arish here is picture of a Stewart Warner Crank Shaft Balancer similar to the one the shop who did our balancing used. You can see the adjustments to the counter weights are made with a belt sander, I don't think any of our cranks were so far out that they had to take metal away by drilling. Our pistons did have metal removed from the underside using an end mill.

johneeb wrote:

hilltop170 wrote:I wonder what the dynamic balance on this is?

Probably measured in ft-lb!

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Richard, do you put lights on that at Christmas time?

Good idea John! It's in Del's shop in Mena, AR