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Engine Building Advice


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#1 28hodge

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Posted 07 April 2020 - 10:42 AM

As I am on furlough and bored I dragged the spare engine I got out of storage. I've rebuilt 2 strokes and 4stroke heads on motocross bikes but not bottom ends, as I have a engine that's basically in bits I thought I might as well learn now.

This engine owes me nothing as I was kind of given it (not strictly true, a lad owned me £100 and said I could have this instead)

It’s kind of complete but missing bits, it’s a a series block on original bore with pistons and crank installed though with a boat load of end float so I am assuming it's been put together for safe keeping without the correct thrust washers.

I’ve had a quick glance over it and first thing I notice is that the nose of the crank is very tarnished, it’s rough though not deeply pitted and marked. Given the current situation what’s the best way to get this cleaned up? Can I do it myself at home or do I need a engine shop to polish it (not an option currently due to the lockdown etc)

I also have a full remote gearbox, my current mini has a rod change box, if I can get hold of a rod change case can I swap the innards of the remote box into the rod change box?

I'm not after spending loads of money on this, it's basically something to do, that said I don't mind spending on tools as they are always useful, what I'm getting at is if it needs a new crank etc then I'll leave it alone

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Edited by 28hodge, 07 April 2020 - 01:12 PM.


#2 GraemeC

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Posted 07 April 2020 - 11:38 AM

That crank tail might clean up - some long strips of medium emery would be the way I'd go.



#3 DeadSquare

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Posted 07 April 2020 - 02:15 PM

That crank tail might clean up - some long strips of medium emery would be the way I'd go.

 

A brass wire brush, followed by wire wool and Brasso would be better, but start by washing the diva gear in solvent and than soaking it in clean engine oil until you assemble the engine, then wipe it and fit it.


Edited by DeadSquare, 12 April 2020 - 06:43 PM.


#4 28hodge

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Posted 08 April 2020 - 08:17 PM

Thanks for the pointers, I spent 5 mins with some 600grit wet and dry and it came too a lot, I'll get some metal polish and carry on, it's smooth to touch so no pitting.

I've pulled all the rods off the crank and they are all 1.720 so 30 grind and then removed the crank and the mains are 1.980 so 20 grind and ordered the required bearings, the block has been decked it's like someone started a rebuild on it and dry built it with Pistons to deck the block then stopped, the shells in it are the correct size but have been run but again the oil pump is unmarked, it's got oil (black used oil) in it so again has been run but it's spotless.

So far I have ordered some std thrust bearings to figure out end foot, though I think from measuring I'll need a 30thou oversize to linish to get the end float correct and then all the correct shells, journals look good.

I have 2 12g940 heads but both need rebuilding and I'll get a vernier duplex cam and sw5-7 cam and build it up so far I think, I kinda just want it as a complete engine that I can use if the current one plays silly buggers. The pistons are he polite 20142 on std bore so it's never going to be a monster

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#5 28hodge

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Posted 09 April 2020 - 03:39 PM

the gearbox is an ad016 I think as the mount plate is for bolts from the side and not the face, however the laygear is the close ratio from what I can tell, it's not stamped 22G1040 but is stampe M.E which I think some were, however the first motion gear is 18 teeth which from reading on calver website identifies it as a C/R box.

I am right in thinking this can be built into a standard rod change case?

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#6 28hodge

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Posted 12 April 2020 - 05:58 PM

Std thrusts put in and still got 0.040 float if I get a set of 0.030 thrusts and and set of 0.005 (seen some on eBay, thought they only came in 0.003 over or 0.006) then I can get it back to tolerance. I’ve got a dial gauge on order to check a bit more accurate as use my digital verniers at the minute but I can feel the movement and see it so it’s too much.

Calculated C/R today which came back to 9.5 with the head that I have which has had a very minor skim, will check the other head tomorrow as would like something between 9.75 and 10. To be honest it will be fine with 9.5,it needs to be driveable not chasing bhp.

Gearbox I’ll try to swap into a DAM5626 or a 22g1382 I think as my other engine and box are A+ it makes more sense to build this up onto an A+ box so that I can swap the blocks and gearboxes around if I ever need too.

I really need to get the block cleaned as it’s grubby inside and not really able to clean it well enough by hand with what I have (brake cleaner and torq roll) but nowhere is open to get it cleaned as I also want some fresh can bearings pressing into the block so I might build it to a point then park it till normality returns.

#7 Ado1379

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Posted 10 May 2020 - 05:58 PM

Hi mate, how far did you get with this? I managed to clean my box and block with a couple of wire wool drill attachments and lots of beer (for me ?). As for cam bearing I made my own out of some washer and a long bolt. (Used a digital vernier to get exact measurements). I’m basically at the point of getting the block and cylinder head faced and I can start rebuild. My question is, you stated you have 0.040 play on end float. I have just under this about 0.036. I thought that would be ok but I’m now guessing no?

#8 28hodge

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Posted 10 May 2020 - 07:28 PM

I kinda parked this and took the current engine out to clean up the engine bay and investigate a odd rattle I had which looks like it may have been coming from the end float on the primary gear being too much, then I decided to check the mains and found some unexpected wear, so I’m rebuilding that engine first.

End float should be 0.003-0.007 I think but check that in Haynes/forum I think I was aiming at 0.005.

I by no means know what I’m doing, I’ve not rebuild an a series before but they are pretty simple things

Edited by 28hodge, 10 May 2020 - 10:10 PM.





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