What went wrong here on this crankshaft ?

I have built a crankshaft like this before for the Bengs flame eater and I did not have any problems. But when I attempted to build a second one with the supplied crank plates I found that the small and large cranks are out of alignment ie. not in the same plane when looking from the top. What went wrong here ?

The holes are already predrilled (about 5.9mm). I only had to ream them out to 6mm on my drill press as I did before.

Edited By Brian John on 23/07/2016 08:08:35

Edited By Brian John on 23/07/2016 08:08:55

Did you have the two crank webs glued/soldered/clamped firmly together when you reamed them? Are the two webs in the same position relative to each other as when they were reamed?

If so, they must have not been sitting dead square to the reamer when you reamed it. Perhaps the drill press table is has moved and is not square to the Z axis? Or a bit of swarf got between the crank web and the drill table during the reaming of one hole?

Could also have been the jaw lifting on you drill vice which would tilt the web and make it ream crooked.

Did you hold anything against the two webs when glueing? if there was a bit of play or tightness in the fit they may not self align. I don't use loctite often but if building this crank would do it in two stages. first being teh pin into the two webs with teh main shaft left loose, laid on it side to keep the two webs parallel. When that has set I would stick the shaft with it hanging as you have in the photo.

Heat it up to break the loctite joints, clean well and try to find the fault before loctiting again.

1. No, I did not join the two crank plates together. I should have, but I managed without doing that the first time...probably a fluke !

2. The drill press table cannot be moved as the nut is on too tight. I did try when I first bought it but it will not budge so I decided to leave it like that...good thing too.

3. The instructions say not to hard solder these parts due to the risk of distortion. What do you think ?

Edited By Brian John on 23/07/2016 10:38:47

It might be worth trying the effect of turning one of the crank plates over, so that the face on the outside becomes the inside. It is possible that the two parts were reamed together but slightly out of true, and then they were assembled with one plate inverted.

If the crankpin is indeed cock-eyed as described, the effect will be to move the little end from side to side in the piston* and to twist the piston* in its bore, as the engine rotates.
*Or the cross head, in a double-acting engine, of course.

Cheers, Tim

I think Loctite is more than up to handling the massive power of the flame licker.

Having a breaker bar around and a set of sockets can be useful at times Brian. You may already have a socket set. If you buy a breaker bar look for a very long one.

Parts like these really need making together. Having the holes pre drilled makes things more difficult but does set the centre distance for you.

Given that the holes are there personally I would turn something up that was a close fit in them. Use that in one pair of holes to align them and probably make it long enough to allow it to be held in the drill chuck to align them to that as well. Remove and then ream that hole. Fit a short piece of the final shaft in that hole and then ream the other.

If the drilled holes could be enlarged a touch I would drill before reaming as it will help the reamer produce a more accurate hole. Even when set up like this there will probably still be some miss alignment relative to the holes and drill spindle.

There are all sorts of problems though.

Vice jaws may not be square - the ones you have aren't suitable but it looks like you could make some plain ones for it. Aluminium would be ok. In my view anyway or use steel.

The drill table is probably not square to the drill.

Other than the jaw shape these aren't a problem providing that the shaft holes are parallel to each other which they will be of done in the same setting. They may cause a problem if the little end is a very close fit width wise.

I don't think I would try sticking them together so you could use the ledge on your vice jaws. Feel free to try it though.

Rather than make new vice jaws you could keep your eye open for vices like this

**LINK**

They generally are dead square all round if used and dated. Some have small V's on one jaw for round work but they are not positioned or sized so that they can't be used for square stuff. I usually drill onto MDF or a bit of scrap aluminium or what ever I can find when drilling straight through in a vice like this. MDF is generally rather flat and parallel over short distances anyway.

As loctite will gap fill a bit you could try aligning the main shaft holes as described and re reaming the little end. Then loctite up while they are both held correctly in a vice.

John

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Tim : I have tried every variation of putting them together but nothing corrects the problem. I was surprised as I thought it would just be a matter of switching them around to get it all lined up.

Hopper :I was thinking more in terms of future projects which might use something similar rather than this particular flame licker

Ajohnw : I am not keen on moving the drill table. It is square now and moving it will only cause problems when trying to get it square again. I am glad that I could not undo the nut when I first tried ! If I need to drill on an angle for flywheel grubscrews then I put a piece of timber under the vice.

I am looking at new vices now ; I just have not decided on anything yet.

What puzzles me is that I did not have any problem making the first crankshaft using this vice, this drill press and this method ? Of course, it could be that the holes on this set were not drilled square when I got it but I admit that is very unlikely. But I will check next time before I start drilling or reaming !

Edited By Brian John on 23/07/2016 13:22:06