CSR speed problems

[Apachemax]

I understand everyone is at the nationals and the chances of me getting a quick response are fairly low, but nevertheless, heres the situation.
We built a sorenson roll up C runabout for Top O'. Bought a brand new 302, and installed a fuel pump. Unfortunately, the only prop that fits is our 20ssh prop, since my "302" prop has an unusual 5/8" hub.
So finally, heres the problem, while testing it only achieved a top speed of 53mph. Isnt that nearly 15mph slower than what a typical CSR runs? Even considering a small prop, shouldnt i see speeds of the high 50s? My 302 has been timed as instructed in the owners manual. Also, what fuel mixture is recomended for a Yamato?
Any and all info is greatly appreciated!
-Brandon
521w

[bh/]

my "302" prop has an unusual 5/8" hub.

I think if u measure it, it will be 16mm
5/8" is exactly 15.88mm
302s came with 16mm prop shafts, and props.
So not really unusual.

[Apachemax]

my "302" prop has an unusual 5/8" hub.

I think if u measure it, it will be 16mm
5/8" is exactly 15.88mm
302s came with 16mm prop shafts, and props.
So not really unusual.

I attempted to put my 16mm shaft through it, and the shaft is too big.
I have no experience with anything bigger than a yamato. Does D class engines use a 5/8" shaft?

[jeff55v]

D class uses 11/16" propshaft.

[Apachemax]

Its engraved with "dewald" along with the normal numbers on one of his props. Is anyone willing to PM me his number?
Thanks!

[bill van steenwyk]

if you have a prop that was not made specifically for a 302, it could be a PRO prop. Most of those are 15MM shaft size and Dewald makes a lot of PRO props, and some PRO props will run on a 302 depending on what class they were made for originally and the gear ratio of same.
, and the 302 shaft was turned to 15MM or the prop was shimmed to the right size from a larger size.

It is very hard to measure inside diameters correctly unless you have inside micrometers, especially if you are using a dial caliper. You may get one dimension one time and another the next time, one right after another.

As Brian said 15.88 MM is 5/8 but unless measured correctly/exactly with the right measuring tool, very close to 15MM also. Tape measures or even machinist rules are not the right tool to get the correct measurement with.

[Danny Pigott]

302

How is the fuel pump installed ? there are a couple of ways to do it. ck. float level in carb. it is in the book how to do it. It may still be the prop just a couple things to ck. Dewald can shim the prop for you.

[seanp3]

I understand everyone is at the nationals and the chances of me getting a quick response are fairly low, but nevertheless, heres the situation.
We built a sorenson roll up C runabout for Top O'. Bought a brand new 302, and installed a fuel pump. Unfortunately, the only prop that fits is our 20ssh prop, since my "302" prop has an unusual 5/8" hub.
So finally, heres the problem, while testing it only achieved a top speed of 53mph. Isnt that nearly 15mph slower than what a typical CSR runs? Even considering a small prop, shouldnt i see speeds of the high 50s? My 302 has been timed as instructed in the owners manual. Also, what fuel mixture is recomended for a Yamato?
Any and all info is greatly appreciated!
-Brandon
521w

A "brand new" 302 is going to come with rings when it was ran in Japan. I would guess your compression is going to be a bit low. A new set of rings should perk up the motor. If you want to perk it up a bit more have the head shaved to minimum cc's (25.5 if its has 14mm plugs). Also, a new 302 gear foot is pretty clubby and needs to be shaped. This will also help you pick up more speed and give you better handling. Has anything been done to the motor other than what you listed above?

[pat]

I doubt that you would expect to get 68 mph with a roll-up marathon CSR. It would take a very special hull, engine, prop and set-up combination to be in that speed range. I would say if you are running a CSH that would be an expectation. I would look for a bigger blade 20SSH prop since a CSR would have very similar pitch requirements but maybe a little more leading edge cup than a 20SSH would have and more blade area. You may want more advanced timing than what is spec and your high speed fuel mixture setting is also important. Get a Tiny Tach otherwise you are in the dark. You may find that 53 mph equates to low rpm as well.

[ZUL8TR]

302 speed

Do you have a tach? Need one to determine what rpm the engine is running with different props.

What piston depth is the engine timed at?

Any idea what the pitch is on the 20ss prop you tried?

Check compression as noted above by seanp3.

Creig's contact info posted on the APBA site, here:

http://www.apba.org/suppliers/dewald-racing-propellers

Carb high speed needle might need adjustment.

Fuel mix is 30:1 per manual. This varies as some run more oil.

http://www.yamatoracing.net/y302manual.pdf

What plugs are in the engine, 14mm or 18mm?

What is the prop shaft end depth below bottom and level, in or out?

[rumleyfips]

Mitch Myer brought three Yamatos into NY in 1979. I bought one and needed a wheel quickly. I ordered a 3 blade cleaver from Ron Hill and got great delivery time. Unfortunately it wasn't very fast: the engine bogged.

Everyone looked and commented. Leigh Furnal tried it on his CSH. Nope too big. Eric Wolfe tried it on his DSH. Nope too big. Must be a COH prop Leigh said. There must have been a misunderstanding about the class .

A guy took it to try on a C alky. I never saw him or the prop again. Oh well.

John

[Apachemax]

My 302 is internally stock besides the fuel pump, shaped gearcase, propshaft.
The prop will be reworked to fit. I suppose i need more C props, and more 20ssh props. As i only have one of each.
I will be doing more testing, so advance the timing a little and lean out the fuel mixture needle? Im not looking to bust any speed records but would like the extra 5mph.
Im also thinking over the winter, having the motor completly redone with new rings, shaved head, and then theres something many people do to the reeds?
All the insight you guys shared is greatly appreciated!

[Apachemax]

Got the prop shimmed, got gas and mixed it 30:1. Ready to head back to the river and test.
Although, i only have a tiny tach, and a water damaged tiny tach, both with 6 foot cords that are too short and wont work (conviently). Is there a way that i can combine the two? Has anyone done this and been successful? Otherwise, what other tach brands do people use on yamatos?

[ZUL8TR]

tach

Got the prop shimmed, got gas and mixed it 30:1. Ready to head back to the river and test.
Although, i only have a tiny tach, and a water damaged tiny tach, both with 6 foot cords that are too short and wont work (conviently). Is there a way that i can combine the two? Has anyone done this and been successful? Otherwise, what other tach brands do people use on yamatos?

Take the tiny tach that works and add X inches of solid core copper 18 ga coated wire. Just splice it into the existing red lead. Add wire needed for the ground. Did this to my Tiny Tach and worked fine. It always gave me erratic issues on the Y80 (point ignition) due to not a clean signal according to TT tech dept, but it works fine on my CD ignition 25ss. So your CD ignition 302 should not have a problem with the added length of wire.

[pav225]

My 302 is internally stock besides the fuel pump, shaped gearcase, propshaft.
The prop will be reworked to fit. I suppose i need more C props, and more 20ssh props. As i only have one of each.
I will be doing more testing, so advance the timing a little and lean out the fuel mixture needle? Im not looking to bust any speed records but would like the extra 5mph.
Im also thinking over the winter, having the motor completly redone with new rings, shaved head, and then theres something many people do to the reeds?
All the insight you guys shared is greatly appreciated!

We'd be happy to help. Call me next week, or we can talk at Neosho.

Mike