Sparey Diesel Crankshaft

[Clive Brown 1Participant @clivebrown1]

I’m making the 5cc Sparey Diesel to Hemingway’s plans. The crankshaft is specified as from 1.25″ dia steel bar. In particular, the overhung crank-pin looks to be an awkward machining operation. I’m wondering if a press-fit or loctite assembly might be OK. Perhaps also even for the crank web onto the shaft itself.

Any thoughts or experience of such construction?

[JasonBModerator @jasonb]

machining is not too hard, you can either use  a keats type angle plate or bore  a block of aluminium to clamp the shaft in then the block can be held in the 4 Jaw. If going for an integral pin then you can mill a lot of the waste away to leave a small square that can be easily turned and a clean up facing cut to the web.

I have also done pressed in silver steel pins, a hand reamer not run all the way through will leave a taper that grips the pin more the further it is pressed in.

[Clive Brown 1Participant @clivebrown1]

Thanks for such a quick response JasonB. How do you manage such relevant pictures at a moments notice? My Keats angle plate is a fairly big thing and doesn’t really appeal for this job. The aluminium block looks better to me, but the shaft will need tight clamping. i think that might be the way to go though.

[bernard towersParticipant @bernardtowers37738]

When I made mine as all my others I do them all in one as it is imperative that the pin is perfectly in line with the crank

[larry phelan 1Participant @larryphelan1]

Clive,

You wonder how Jason manages to respond so quickly ?

I suspect he must have done these things before !!

[Neil WyattModerator @neilwyatt]

Jason beat me to it.

It’s so easy to do it with the offset clamp, even I managed to do it!

Unfortunately, it’s still 50% unfinished since this photo taken in 2003. Oh heck, that’s 21 years ago…

😧

Neil

[JasonBModerator @jasonb]

That photo looks 100% unfinished too me😊

[Neil LickfoldParticipant @neillickfold44316]

When I was making crankshafts for K&B .21 3.5cc engines, I used a 3/16 needle roller, and used 0.04mm diameter interference fit. When assembled, I used castor oil to help prevent shearing as it was pressed together. I made a guide block to align the pin to the hole and was at the same time, the limiting setting for the amount of the pin from the fly wheel. This is for a competition engine running at 24k in the air. Not high revving to todays  engines. I used a fixture block to offset turn the crank relief and drill bore the pin hole. The needle roller was a better option than the 4340 steel pin turned and polished as a crank and pin. Hindsight I should have made them EN36A and heat treat etc.

The needle roller was turned with a carbide insert and left a very small amount of the radius on the needle roller side that entered the bored hole. I used 4340 for the crank and web. I did not have a mill in those days, so hacksawed and filed the flywheel and filed/dremel the induction port. They worked very well.

Now days, the crank pins on the competition engines have a slight taper of about 0.01mm to 0.02mm on diameter and are smaller at the flywheel side. This aides in keeping the conrod on the pin and reduces/ prevents the rod from rubbing on the backplate. Some taper the conrod bush to match, while others leave the rod bush parallel. They both work well.

[JasonB]

On JasonB Said:

That photo looks 100% unfinished too me😊

“since”

[JasonB]

On JasonB Said:

machining is not too hard, you can either use  a keats type angle plate or bore  a block of aluminium to clamp the shaft in then the block can be held in the 4 Jaw. If going for an integral pin then you can mill a lot of the waste away to leave a small square that can be easily turned and a clean up facing cut to the web.

I have also done pressed in silver steel pins, a hand reamer not run all the way through will leave a taper that grips the pin more the further it is pressed in.

I like the method of using a block of aluminium to machine the crank pin.

Just a couple of questions though, how did you clamp or hold the crankshaft in the block?, and I assume you bored out or drilled and reamed a hole for the crankshaft, but how did you then set up the block and crankshaft to centre the crank pin to get the required offset?

Regards

Derek

[JasonBModerator @jasonb]

The block is drilled and tapped for two grub screws, M5 from memory. I  put a small piece of soft aluminium wire into the hole before the screw and this saves the screw damaging the shaft.

Held the shaft vertical in the mill, located ctr and then moved the axis by the crank throw and spotted the pins position.

It is then just a case of using te h4-jaw to position th eblock so the spot runs true, similar to this setup for a crankcase.

[JasonB]

On JasonB Said:

The block is drilled and tapped for two grub screws, M5 from memory. I  put a small piece of soft aluminium wire into the hole before the screw and this saves the screw damaging the shaft.

Held the shaft vertical in the mill, located ctr and then moved the axis by the crank throw and spotted the pins position.

It is then just a case of using te h4-jaw to position th eblock so the spot runs true, similar to this setup for a crankcase.

Thanks Jason for a very clear and fast response !

All the best

Derek

[Clive Brown 1Participant @clivebrown1]

As a follow-up; after anguishing about a loctited crank pin, I finally decided to use my Keats angle plate after making a modified clamp for it. I had been concerned about the job shifting under the interrupted cut, but the set-up proved as solid as a rock.

[KEITH BEAUMONTParticipant @keithbeaumont45476]

Although I have used pressed in crank pins  for the last 4 of the engines I have made, when I do machine it from solid I have found using a Stevensons square collet block in the 4 jaw chuck,a simple way of setting it up. Just centre it in your favourite way, then offset it using one direction. When you are happy with the position, it is a good idea to drill a small centre point before any interupted cutting. This acts as a visual check that nothing has moved and if it has ,makes it easy to re position.

I am,in fact ,making a crankshaft by this method at the moment ,for a 1cc Diesel, but have not got to the crank pin yet.

Keith.

[PaulGParticipant @paulg46657]

I have been putting off pressing in a 0.25 inch crank pin myself for too long now! I think I’ve been worrying too much about the fit required and getting the pin square. Can you guys advise:

How much interference should I aim for? I was assuming Loctite could also be used (and I do have a press!). Or even shrink fit?

Do you use a guide (eg a block?) to somehow keep the pin square while pressing in?

Or maybe I’m overthinking again.

Paul

[KEITH BEAUMONTParticipant @keithbeaumont45476]

The method I use is, using a hand reamer in the mill,I gently ream using the taper part only until the pin will just start to enter. I use two pieces of ALI angle in 4 inch vice jaws. Take the leading edge off the pin so that it does not scrape. Put some Loctite in the hole to act as a lube. Line pin up into hole. Place between jaws evenly. Squeeze in about a third of the way. Check for square, At this point if not happy with squareness you can still tap it to correct it. Squeeze slowly until the pin hits the back Ali. Job done!   Good Luck!

Keith.

[PaulGParticipant @paulg46657]

Many thanks Keith. That has given me confidence to get on with it. No way I’ll match your skills though!

Paul

 

[KEITH BEAUMONTParticipant @keithbeaumont45476]

Glad to help,Paul. I should have stressed the importance of taking the leading edge off the Pin. The first two times I tried this method I had trouble getting it exactly 90 degrees. I then realised the sharp leading edge was scraping and able to dig in,causing it to go off square.

Keith.

[PaulGParticipant @paulg46657]

Yes that’s what I was worried about so worth mentioning. I suspect that having a dummy conrod handy might be useful to gauge the alignment. Oddly it’s reassuring to hear that something went wrong for you but that you cracked it in the end!

Paul

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