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Cheap and cheerful motor - Spex - 23-09-2019
Friends,
I would like some advice as to clearances of bearings on a 1-5/16 crank . I have an engine 29-30, that broke a crank ( was1-1/8) but have a 1-5/16 crank that is round and within a thou or so of original size. I also have a nice looking set of rods that have been remetalled smaller and wider, which could be machined again to fit.
This is by way of a "practice" solo rebuild, as My Mechanic friend has left the building, and I have to sort out Two others, (but these are 1-1/2 Phoenix cranks) This car is used very little.
Also, for maching purposes, can someone please tell me the exact distance between centres- Gudgeon pin to Big end.
Any other comments or ideas- all wellcome.
Many thanks in advance.
Cheers, Peter (in OZ)
RE: Cheap and cheerful motor - Bob Culver - 23-09-2019
Blueprint of conrod published a few days ago with centres spacing.
It would be a pity to open good rods out to standard if life not to be long, as good rods precious and unless new any other crank to be used likely to be undersize. Crank life may not be long, especially if any cracks. The rear journal must show no sign of welding, brazing etc. All radii must be intact.
Rods were traditonally fitted to a snug clearance; soon increased as scraping high spots wore off. But good modern practice is a distinct small clearance, esp if crank truly round.
If reusing main bearings acceptable clearance is hard to assess. Almost any perceptible step on outer roller tracks is too much.
Angular contact races with unmarked tracks can be shimmed to restore nil clearance when back to back.
Main danger if unfamilair is breaking the crankcase lip and heavy handedness with threads generally.
There are a myriad pitfalls but anyone with an instinct for what is correct and good practice can spot many. A trawl thru the Forum helpful. Contact with someone Seven expereinced the ideal.
RE: Cheap and cheerful motor - "Slack Alice" Simon - 24-09-2019
If you can get some other rods to play with it is a great learning curve.
If it doesn't really matter - old bent rods or whatever - I have opened them out with abrasive paper stuck to a suitably sized socket, then practiced my scraping to get to the traditional 80% contact and "just falling under its own weight" criteria.
If you get it wrong, silver paper shims for fine adjustment.
Or filing the caps and ditto.
Go and play a bit first, then decide.
Sorry to go on, but I find it fun.
And if it is only a "cooking" engine it will tolerate imbalances and inaccuracies and get you around the countryside.
RE: Cheap and cheerful motor - Chris KC - 24-09-2019
If I had a car which is used very little and an original crank within 1 thou of standard I think I'd go ahead and fit it - if it passed a crack test.
RE: Cheap and cheerful motor - Robert Leigh - 24-09-2019
When I first built an improved engine for my Ulsteroid I fitted a Phoenix crank. I had a set of nicely matched rods but they were from a reground crank and were 10 thou undersize. None of the remetallers I found was prepared to take the big ends out to standard size without remetalling so I set to and hand-scraped the ends to fit using the back of a sharpened hacksaw blade. The engine did over 20,000 miles until one of the new little end bolts I had used lost its head. I got away with that, except that the rod cracked as a result.
Robert Leigh
RE: Cheap and cheerful motor - Spex - 24-09-2019
Thanks to all who replied. All comments and ideas noted .
The crank measures well. I have yet to crack test it.
The rods need a fair bit taken out. I have constructed a conrod jig and was going to do the bearing on a vertical mill. I needed the length between bearing centres for this.
I can now finish the jig.
I like to do crazy type things , and remetalling is on my bucket list.
I should learn more about these confusers, especially to do with photos.
Still open to any comments and ideas.
Cheers, Peter
RE: Cheap and cheerful motor - Bob Culver - 25-09-2019
Hi Peter
Ruairirdh regularly obliges with a photo of the v block based lathe jig he and reconditoners commonly used for boring rods. Search will reveal.
RE: Cheap and cheerful motor - Zetomagneto - 25-09-2019
Hi Spex, conrod centres are 6”. I can see no reason why you shouldn’t bore these rods to suit your crank as long as the white metal is in good condition.I know people remachine undersize rods to suit new cranks.I have had rods remachined in the past with good results.
It would be easier if you had a Conrod boring jig on a lathe, but careful setup and adequate holding on the mill should work.
Bearing clearance .0015” to 002”
Be interesting to see your jig/ holding device. Something like this https://www.google.co.uk/search?q=conrod+boring+jig&ie=UTF-8&oe=UTF-8&hl=en-gb&client=safari#imgrc=Ft_4cHARjzEQjM:
Best Wishes Zeto
RE: Cheap and cheerful motor - Ruairidh Dunford - 25-09-2019
The rod boring jig I have, mentioned by Bob above, is like the one below (photo credit to Tony Griifiths at lathes.co.uk) - made for a Myford but fitted to my Boxford via an adaptor plate my friend made.
![[Image: img46.jpg]](http://www.lathes.co.uk/myford/img46.jpg)
RE: Cheap and cheerful motor - Colin Reed - 25-09-2019
HI Spex,
As Zeto has said a jig on a lathe much easily used as you need access to both sides of rod for doing side clearance and radius,
as you need to be able to perform all operations with out having to move the rod once set up.
Cheers
Colin
NZ