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These are both 1275 cranks. The brass plug in the big end journal indicates this is a cross drilled crank and the plug is used to plug off that oil drilling.

justminis wrote:

These are both 1275 cranks. The brass plug in the big end journal indicates this is a cross drilled crank and the plug is used to plug off that oil drilling.

Can you explain this a bit further? I had my crank cross-drilled on the mains and was told by someone to watch out for loss of oil pressure? Mines an A+ crank.

I don`t like cross-drilling cranks,,, it weakens them considerably (IMO)

smiling_simon wrote:

justminis wrote:

Unfortunately, as the mains only have 1 drilling to the big ends, the big ends all get starved for 1/2 a revolution (from 9 o'clock to 3 o'clock, where the load is greatest..

Author:	knuts2au [ Mon Jun 28, 2010 10:59 pm ]
Post subject:	Crankshafts
Ok i seem to have two different types of crankshafts, one has (did have) small brass plugs in the oil holes but have been rubbing and one fell out when the bearing came apart. What should i do with them if we end up using this crank? This crank doesnt have them, looks better condition but haven't measured them yet. Do the part numbers stamped in the cranks tell you anything?

Author:	Convertible Mini [ Tue Jun 29, 2010 6:43 am ]
Post subject:	Crank
It is a 1098 (1100) Crank. Long stroke small bore. Speak to an engineer that "Knows Mini Cranks" (ie G. R.) and that Plug might be able to be re fitted back in the hole or a new one made up and fitted. Do not use without it.

Author:	justminis [ Tue Jun 29, 2010 7:28 am ]
Post subject:
These are both 1275 cranks. The brass plug in the big end journal indicates this is a cross drilled crank and the plug is used to plug off that oil drilling. A new plug could be made but best bet all round is to have the hole(s) tapped and have grub screws fitted. A 6mm grub screw does the job. Take it to an engine shop to have done, don't try it at home. All my race cranks are done that way and had to have it done to a 1100S crank (same as yours) recently as well.

Author:	smiling_simon [ Tue Jun 29, 2010 2:53 pm ]
Post subject:	crank
justminis wrote: These are both 1275 cranks. The brass plug in the big end journal indicates this is a cross drilled crank and the plug is used to plug off that oil drilling. Can you explain this a bit further? I had my crank cross-drilled on the mains and was told by someone to watch out for loss of oil pressure? Mines an A+ crank.

Author:	drmini in aust [ Tue Jun 29, 2010 7:23 pm ]
Post subject:	Re: crank
smiling_simon wrote: justminis wrote: These are both 1275 cranks. The brass plug in the big end journal indicates this is a cross drilled crank and the plug is used to plug off that oil drilling. Can you explain this a bit further? I had my crank cross-drilled on the mains and was told by someone to watch out for loss of oil pressure? Mines an A+ crank. Many small journal 1275 cranks (including Cooper S) had the big ends drilled as normal then cross drilled, and the original outer hole plugged with these brass plugs. The idea was not to get more oil up there, but to put the oil into the bearing at a lesser radius from the crank axis. This reduces oil throwoff due to centrifugal force. With A+ engines the designers thoughtfully(!!??) put a plain bearing into all 3 main bearing caps, with no oil groove. This was ostensibly to give greater load bearing capacity for turbo engines. Unfortunately, as the mains only have 1 drilling to the big ends, the big ends all get starved for 1/2 a revolution (from 9 o'clock to 3 o'clock, where the load is greatest.. There are 2 ways to fix this: 1. Use A series bearings (cheaper, too). You just need to provide an offset tang slot for the bearing shells. or, 2. Cross drill the mains so there are 2 oil pickup points to the bigends.

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Crankshafts https://www.ausmini.com/forums/viewtopic.php?f=2&t=64053	Page 1 of 1

Author:	TheMiniMan [ Tue Jun 29, 2010 8:02 pm ]
Post subject:
I don`t like cross-drilling cranks,,, it weakens them considerably (IMO)

Author:	drmini in aust [ Tue Jun 29, 2010 8:23 pm ]
Post subject:
TheMiniMan wrote: I don`t like cross-drilling cranks,,, it weakens them considerably (IMO) When I do A+ motors I fit A series bearings. The last 1293 A+ I did up, all 4 crankpins were worn oval and the big end shells stuffed.

Author:	knuts2au [ Tue Jun 29, 2010 9:40 pm ]
Post subject:
The crossed drilled crank is the one in best condition, the mains on the other have grooves worn in them. The brass plugs have a small hole drilled so they dont actually completly blank off. As you can see they have been rubbing and one was missing altogether. So which is the best to use, get new plugs fitted (assuming the journals all pass) or get the second crank's, journals ground done a size?

Author:	drmini in aust [ Tue Jun 29, 2010 10:13 pm ]
Post subject:
I'd put grubscrews in the crossdrilled one.

Author:	knuts2au [ Tue Jun 29, 2010 10:23 pm ]
Post subject:
The plugs still had small holes in them, drill holes in the grub screws as well?

Author:	drmini in aust [ Tue Jun 29, 2010 11:00 pm ]
Post subject:
If you want, doesn't matter really.

Author:	smiling_simon [ Wed Jul 07, 2010 9:18 am ]
Post subject:	Re: crank
drmini in aust wrote: smiling_simon wrote: justminis wrote: Unfortunately, as the mains only have 1 drilling to the big ends, the big ends all get starved for 1/2 a revolution (from 9 o'clock to 3 o'clock, where the load is greatest.. Yep I get you. So what do the G.R. mini cranks have? Are both big ends and mains cross-drilled or just the mains?

Author:	drmini in aust [ Wed Jul 07, 2010 4:54 pm ]
Post subject:
I'm not sure what drillings are in his smick 8 counterweighted race cranks from Melbourne.. But I know he prefers using A series bearings too in an A+ block. They eliminate the lube starvation problem without any crank drilling.

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