Wedge the crank then linish the sharp edges, before you grind it.
Then get it dynamically balanced.
The standard 12G1505 big journal crank has very poor counterweighting, wedging it improves the balance factor.
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| 1275 stroker https://www.ausmini.com/forums/viewtopic.php?f=5&t=61096 |
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| Author: | Goldbrocade_62 [ Sun Feb 14, 2010 8:41 pm ] |
| Post subject: | 1275 stroker |
How much clearance should I aim for on the centre main thrust washers ,are standard head studs good enough and should I use a metro tubo head gasket car is for road use only |
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| Author: | 1018cc [ Sun Feb 14, 2010 8:52 pm ] |
| Post subject: | |
1) I'm looking to do the same thing soon (hopefully) I've read to aim for 0.006 - 0.008" for the thrust washers 2)Standard head studs should be ok if in good nick. Convert over to 11 studs if you are still running 9. No doubt you will be running higher compression than standard. 3)Use a BK450 H/G. |
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| Author: | drmini in aust [ Sun Feb 14, 2010 8:53 pm ] |
| Post subject: | |
I used .007" on the thrust washers of my 1412 stroker, on Graham Russell's recommendation. I now use the same in my 1360. I would say .006" is minimum. These cranks flex more with longer strokes. If they grab the washers due to insufficient clearance, it makes a mess of them, and the crank centre main. If oil cannot get out of the centre main due to lack of thrust clearance, the bearing overheats. I found this out with my 1360 as original build. Stock 1275 head studs are OK (not the current NEW stock ones) but if you can afford it, buy ARPs. Do not use thin flat washers, they are useless and soft. With stock studs either use 998 flanged nuts or the thick original washers. The Metro turbo gasket BK450 is hard to beat, for road or track. I use nothing else on 1275 builds I do. <edit> I agree, tap the block whilst it's out for 2 extra studs (or 1x 5/16 UNC bolt and 1x extra stud like an S) |
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| Author: | douglas42l2 [ Wed Feb 17, 2010 9:49 am ] |
| Post subject: | More tips ? |
Am also looking at 40 thou over bore and stroked crank to make it 1360. Any other tips/things to look out for on the build ? |
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| Author: | drmini in aust [ Wed Feb 17, 2010 3:03 pm ] |
| Post subject: | |
Wedge the crank then linish the sharp edges, before you grind it. Then get it dynamically balanced. The standard 12G1505 big journal crank has very poor counterweighting, wedging it improves the balance factor.
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| Author: | sgc [ Wed Feb 17, 2010 3:13 pm ] |
| Post subject: | |
drmini in aust wrote: Biggest. Centre. Main. Strap. EVER! 
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| Author: | drmini in aust [ Wed Feb 17, 2010 3:30 pm ] |
| Post subject: | |
... yer and it's EN25, verrrrrrrry tuff stuff! 
Look closer and you can see that I didn't machine the original cap flat all over, I just surface ground the top lightly to clean it up. I then made the strap preload the cap by .001" or so. There really is no need for this on a road car, but this motor was previously a 1310 with a Cooper S crank. I used to spin it over 8000rpm on track days. [edit] BTW the rod bolts & nuts shown are modified `ARP' BB Chevy. I normally use BB Ford ones but I've had these 8 sitting here in a box for 10 years, so I thought what the hell.. why not. I guess I can fit a bowtie badge to the rocker cover now. 
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| Author: | drmini in aust [ Fri Jul 09, 2010 10:06 pm ] |
| Post subject: | |
Well it's in my Mini now, spinning a remote box with new Mk2 S gears in and a 3.44 diff. Cam is an RE13 with Toyota Corolla rockers. I put smaller (36mm) chokes into the 45 Dellorto to help the midrange. Compared to the previous 1360 (with bigger, RE282 cam) it has lots more low and midrange torque, I've not had it over 6000 yet but it sure gets up there quick! It's nice and smooth too with the wedged + balanced crank. 
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| Author: | TheMiniMan [ Sat Jul 10, 2010 1:29 pm ] |
| Post subject: | |
I would allow 5-6 thou clearance on the upper thrusts,,, but i set the lower thrust clearance at 12-15 tho,,, lets the crank flex a little without grabbing the lower thrusts , helps stop the crank pushing on the cap, working on the bolts, flexing & fatiguing & eventually braking the bolts I`m not a big fan of main cap straps,,, long main bolts & such |
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| Author: | david rosenthal [ Sun Jul 11, 2010 5:40 pm ] |
| Post subject: | |
TheMiniMan wrote: I would allow 5-6 thou clearance on the upper thrusts,,, but i set the lower thrust clearance at 12-15 tho,,, lets the crank flex a little without grabbing the lower thrusts , helps stop the crank pushing on the cap, working on the bolts, flexing & fatiguing & eventually braking the bolts
I`m not a big fan of main cap straps,,, long main bolts & such I would agree with Matt. With many types of engines years ago I did straps with all sorts of mounting methods , I found that overall they did not help that much. The problem is the original material, cast iron is not a good material for this job and even with a strap when I had cap failure quite often the cap was cracked and although the strap stopped it from falling off the cap still moved and chewed the bearing out. Bolt strech was also a problem. If you need to beef up the center main then use a steel cap strong enough. One other mod I do with the thrusts beside what Matt does , is to drill a 3/64" hole thru the block each side to allow oil from the bearing gallery to flow out to the thrusts. Then drill a feed hole thru the thrusts. This way go get a good supply of oil to the thrust faces . I also fit a 1/16" roll pin to the block side thrusts to make sure that they held is place and do not move as the thrust comes on and off. If they move around even a small amount ,they will fret into the block and wear the back or the thrust side, or get a "wedging effect" and cause failure. |
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| Author: | drmini in aust [ Sun Jul 11, 2010 7:56 pm ] |
| Post subject: | |
This thing is only a road motor, running an orange dot diaphragm and std AP drive plate. It'll seldom go to 6500, let alone 7000. The only time I ever had a thrust prob was when I built the 1360 motor the 1st time, and used .003" end float as in the books. .003" just ain't enough, unless you never go over 5,500 rpm. |
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| Author: | kiwiinwgtn [ Sun Jul 11, 2010 10:06 pm ] |
| Post subject: | |
Just wondering after reading the posts, Is the addtional clearance of the thrust used just in stroker engines or all engines Does drilling a hole to lube the thrusts cause a redution to oil flow to the centre main, also do you pin thrust at one end away from the oil feed hole Very interesting post Thanks Kiwiinwgtn |
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| Author: | drmini in aust [ Sun Jul 11, 2010 10:34 pm ] |
| Post subject: | |
kiwiinwgtn wrote: Just wondering after reading the posts, Is the addtional clearance of the thrust used just in stroker engines or all engines
Does drilling a hole to lube the thrusts cause a redution to oil flow to the centre main, also do you pin thrust at one end away from the oil feed hole Very interesting post Thanks Kiwiinwgtn All 1275 cranks flex, strokers more than most. My 1360 (Mk1 S crank) peeled scales of bronze off both the front and rear thrusts with .003" clearance- it damn near spun the centre main bearing too. I reckon .007" (for any 1275 crank) is the go, .003" is way too little. Oil flows from the centre main TO the thrusts- GR puts a slight bevel on one side of a shell for a little more flow. |
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| Author: | david rosenthal [ Mon Jul 12, 2010 3:26 pm ] |
| Post subject: | |
I might be going over the top with some of the mods I do, but things like bearings and thrusts are very important if you push a engine. I always check the flatness of the thrusts on a surface plate and the std set up if the thrust keeper is worn the they will fret and wear. I have found the ends of the unlocated thrust that have been wearing into the fixed one and the ends have started to ride up. This will cause a tight spot on the crank face. Pinning them stops any movement and holds them onto the block/cap. As for drilling it ensures that there is oil flow directly onto the thrust face. I do both top and bottom thrusts on each side but on a std cast cap it will weaken it a bit so I would not recommend it. As for oil flow a std mini pump with good clearances in the engine will over sluppy the required oil for the engine. I would rather have it flowing over the thrust instead of just dumping back to the sump. Matt and Doc know well that the cranks will flex and I believe that if you hold them too ridged then this will cause breakages. What Matt is getting at is allowing the maximum load to be taken on the block thrust instead of the cap/bolts. |
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| Author: | GT mowog [ Mon Jul 12, 2010 4:57 pm ] |
| Post subject: | Re: 1275 stroker |
Goldbrocade_62 wrote: .............. and should I use a metro tubo head gasket car is for road use only
The currently available BK450 are crap, do not fit one. These are nothing like the BK450 of 'old'. |
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