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Where to buy a new crank
- Thread starter MY66AH
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I've never built one but read quite a bit about them....just don't remember where!
As mentioned, line boring may be best but there are other trick's to get it to work best. Was the engine leaking a lot from the rear main? If not then I would just try to get it tight but with a minimum of clearance. Best defer to some of the experts on here. Gerard, Hap, Bill M????
Kinda into Datsun swap's myself.
eaceful:
Kurt
As mentioned, line boring may be best but there are other trick's to get it to work best. Was the engine leaking a lot from the rear main? If not then I would just try to get it tight but with a minimum of clearance. Best defer to some of the experts on here. Gerard, Hap, Bill M????
Kinda into Datsun swap's myself.
eaceful:Kurt
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https://gerardsgarage.com/Garage/Tech/SealKit/SealKit.htm
This lists for a 1275 engine. Gerard is on the forum and should be along shortly
G
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Where has Hap been? I havn't seen him in a while.
Gerard
Luke Skywalker
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Thanks JP. I now have them for all size engines, but most people build the 1275's these days, so I only make a couple of the other sizes.
At an absolute minimum, you must line bore the engine with the half moon seal in place, and NOT remove it once it's been honed or bored. Many shops don't have experience with these small engines and either don't have the tools small enough or don't understand the importance of getting the tolerance right. Clearance need to be between .0015 to .004.
My seal kit is not only an alternative to getting this right, but since my design still incorporates the scroll seal function, it's also a backup system. Feel free to ask any questions.
Gerard
Luke Skywalker
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Are you asking about the seal kit? I'll send you a PM.
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Here is what Gerard says : https://www.gerardsgarage.com/Garage/Tech/MOWOG.htm
Here is what New Zealand says https://sites.google.com/site/minif...ripes---colours/mini-s-badges/the-mowog-story
Closer to the truth is this: I always remember [FONT=Verdana, Arial, Helvetica, sans-serif]MOWOG[/FONT][FONT=Verdana, Arial, Helvetica, sans-serif] as the name of the silverback gorilla employed at BMC to tighten all the nuts and bolts up so that us mere mortals can never get them undone ever again... (Or a mythical creature with the strength of a gorilla, 6 inch thin fingers, triple jointed and only three feet tall. Sometimes when you are in the garage, you might catch the sight of one out of the corner of your eye - having just placed the nut or bolt you were looking for in the most inaccessible place possible in memory of a time in history when its official job was to wreak mechanical [/FONT][FONT=Verdana, Arial, Helvetica, sans-serif]mayhem[/FONT][FONT=Verdana, Arial, Helvetica, sans-serif] on a world wide car industry.[/FONT]
Here is what New Zealand says https://sites.google.com/site/minif...ripes---colours/mini-s-badges/the-mowog-story
Closer to the truth is this: I always remember [FONT=Verdana, Arial, Helvetica, sans-serif]MOWOG[/FONT][FONT=Verdana, Arial, Helvetica, sans-serif] as the name of the silverback gorilla employed at BMC to tighten all the nuts and bolts up so that us mere mortals can never get them undone ever again... (Or a mythical creature with the strength of a gorilla, 6 inch thin fingers, triple jointed and only three feet tall. Sometimes when you are in the garage, you might catch the sight of one out of the corner of your eye - having just placed the nut or bolt you were looking for in the most inaccessible place possible in memory of a time in history when its official job was to wreak mechanical [/FONT][FONT=Verdana, Arial, Helvetica, sans-serif]mayhem[/FONT][FONT=Verdana, Arial, Helvetica, sans-serif] on a world wide car industry.[/FONT]
Spridget64SC
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The 3 with the arrow on top is the factory piston oversize. Early A series engines had factory sizes from 1 to 4. 1 being standard and 4 being the largest oversize. Rare to find a 4. Usually blocks were all oversized the same on each cylinder, but have found them mixed as well. A recent 1098 block showed two cylinders with a 2 oversize and two cylinders with a 3 oversize.
"2013" is the piston part number. The last digit corresponds to the oversize. Hence the 2013 matches with the "3" oversize.
The "Front" corresponds to which orientation the piston must be placed on the rod. Could be because of an offset in the piston pin location in the piston or because of a split in the piston skirt for noise. Other types of engines use the "front" orientation because of valve reliefs, dish locations or other piston to head situations.
"P3" is likely some kind of manufacturing date or location code. Maybe both.
There is probably some markings on the inside of the piston as well. Alloy types or other part number information. Maybe a symbol for the actual manufacturer such as Hepolite, AE, Nural or such.
HTH,
Mike Miller
"2013" is the piston part number. The last digit corresponds to the oversize. Hence the 2013 matches with the "3" oversize.
The "Front" corresponds to which orientation the piston must be placed on the rod. Could be because of an offset in the piston pin location in the piston or because of a split in the piston skirt for noise. Other types of engines use the "front" orientation because of valve reliefs, dish locations or other piston to head situations.
"P3" is likely some kind of manufacturing date or location code. Maybe both.
There is probably some markings on the inside of the piston as well. Alloy types or other part number information. Maybe a symbol for the actual manufacturer such as Hepolite, AE, Nural or such.
HTH,
Mike Miller
Spridget64SC
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Actually, the factory oversizes are closer to thousandths rather than 10's of thousandths. A 2 would be for a bore that ended up about two thousandths over the upper limit on bore size.
I'll check tonight and see if some of the literature I have at home shows the ranges. I think Bentley mentions the oversizes on one of the pages of engine specs.
C = pi x D. So, a 0.001 increase in bore diameter increases ring gap by 0.0031" A couple of thousandth's over on the bore and the ring gap gets too big and the piston noise in the bore starts going up due to the increase in bore clearance.
1275 pistons went up to a 3 oversize before they dry-sleeved the bores. One see's quite a few sleeved 1275 blocks. Good for 1380's, but not good for a +40 race engine.
Mike
I'll check tonight and see if some of the literature I have at home shows the ranges. I think Bentley mentions the oversizes on one of the pages of engine specs.
C = pi x D. So, a 0.001 increase in bore diameter increases ring gap by 0.0031" A couple of thousandth's over on the bore and the ring gap gets too big and the piston noise in the bore starts going up due to the increase in bore clearance.
1275 pistons went up to a 3 oversize before they dry-sleeved the bores. One see's quite a few sleeved 1275 blocks. Good for 1380's, but not good for a +40 race engine.
Mike
Spridget64SC
Jedi Trainee
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With the 1275 factory sleeves, the walls get too thin. The OD on the factory sleeve is just 2.870" If you bore out to a +.044" (custom pistons) with 0.003" clearance (SCCA limit is 0.047") the bore ends up at 2.828". The sleeve runs out of thickness.
I have sleeved 1275's for racing using an aftermarket sleeve. I use a 2.937" OD sleeve from LA Sleeve or turn down an OHIO sleeve or Tiger sleeve and press into the block with a step at the bottom. Factory sleeves only use the press fit. They extend slightly past the bottom of the bore. You can tell if the block is sleeved by removing the distributor retainer and the drive and feeling inside the block at the drive relief area for the sleeves sticking below the #3 & #4 cylinders.
Yes, Chris' engine looks to be still on the factory fitted pistons. Albeit the #3 oversize. The other cylinders may or may not be a #3 oversize. STD rings should fit. Clearance might be a bit on the wide side, but depending upon ring set used, they may have some oversize/wear compensation included. Often, a rebuild ring set has about 0.005" of extra diameter.
Looked last night in two locations and nothing of any detail on factory STD piston oversizes. They mentioned the usual +10 to +40 oversizes, but not the stuff for block boring "oops".
FWIW, Late 1275s dropped the last factory oversize and change to a letter code. Only A and B factory oversizes show up. Have never seen a "C" sized piston in the later black painted engines.
Have a great weekend. I'm off to Roebling Road for some racing. Mike
I have sleeved 1275's for racing using an aftermarket sleeve. I use a 2.937" OD sleeve from LA Sleeve or turn down an OHIO sleeve or Tiger sleeve and press into the block with a step at the bottom. Factory sleeves only use the press fit. They extend slightly past the bottom of the bore. You can tell if the block is sleeved by removing the distributor retainer and the drive and feeling inside the block at the drive relief area for the sleeves sticking below the #3 & #4 cylinders.
Yes, Chris' engine looks to be still on the factory fitted pistons. Albeit the #3 oversize. The other cylinders may or may not be a #3 oversize. STD rings should fit. Clearance might be a bit on the wide side, but depending upon ring set used, they may have some oversize/wear compensation included. Often, a rebuild ring set has about 0.005" of extra diameter.
Looked last night in two locations and nothing of any detail on factory STD piston oversizes. They mentioned the usual +10 to +40 oversizes, but not the stuff for block boring "oops".
FWIW, Late 1275s dropped the last factory oversize and change to a letter code. Only A and B factory oversizes show up. Have never seen a "C" sized piston in the later black painted engines.
Have a great weekend. I'm off to Roebling Road for some racing. Mike