Basket Case Project - What Have I Gotten Myself Into?
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What price a leak free head? ;-)
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Can somebody explain why the intake valve seat has a bit of a raised lip and the exhaust valve seat is flush with the surrounding head? Mostly I'm just curious.
Also, I measured my valve stems and they are all at 0.31+ which according to my manual is good. That said, how can I determine if I need new guides? I've been digging around and can't seem to find anything definitive on this.
The springs are below the 1.7 inch uncompressed length and after sitting under pressure since the day they were made they probably could do with an opportunity to relax.
Also, I measured my valve stems and they are all at 0.31+ which according to my manual is good. That said, how can I determine if I need new guides? I've been digging around and can't seem to find anything definitive on this.
The springs are below the 1.7 inch uncompressed length and after sitting under pressure since the day they were made they probably could do with an opportunity to relax.
N0rt0nelectr@
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Looking at your pictures of the head it looks as if the exhaust port threads aren't in that good of shape. You might want to look into having Jim Comstock replace them and at that time he can make sure your head gasket surface is flat and he can replace the 3 stud holes with something that won't pull.
I have had the studs pull when tightening the nuts under the exhaust port. To say that I was PO would be an understatement. Having the head vapor blasted will make it shine.
John in Texas
I have had the studs pull when tightening the nuts under the exhaust port. To say that I was PO would be an understatement. Having the head vapor blasted will make it shine.
John in Texas
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I got the cylinder barrels off over the weekend. At first they wouldn't budge but after reading a few other threads I applied a little heat with a torch along the gasket seam and gave it some whacks with a hammer on a block of hardwood pressed into a lip I found between the back of the barrels and the case and I had it off in about 5 minutes.
I also started disassembling down the gearbox.
I'm stuck on the gearbox for the moment because I need to get hold of a wrench large enough to pull the 1 1/2" sprocket nut:
I'm torn over going with a silver or black repaint on the barrels. The stock color was silver but I'm partial to look of the black barrels. My son is pushing for silver and thinks it looks better stock. Oddly enough, my wife can agonize over the correct color for a room but gave me a blank stare when asked if she thought silver or black would be better.
I also started disassembling down the gearbox.
I'm stuck on the gearbox for the moment because I need to get hold of a wrench large enough to pull the 1 1/2" sprocket nut:
I'm torn over going with a silver or black repaint on the barrels. The stock color was silver but I'm partial to look of the black barrels. My son is pushing for silver and thinks it looks better stock. Oddly enough, my wife can agonize over the correct color for a room but gave me a blank stare when asked if she thought silver or black would be better.
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If the pistons are the original type with slots behind the oil rings (see below) then they really should be replaced.
The 040038 ratchet 'hairpin' spring is fitted upside down (although the cover is shown upside down in the photo).
With the cover the right way up.The double cranked 'dog leg' should be at the bottom
comnoz said:
The 040038 ratchet 'hairpin' spring is fitted upside down (although the cover is shown upside down in the photo).
With the cover the right way up.The double cranked 'dog leg' should be at the bottom
wrecks said:
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I have every reason to believe the pistons are original. According to my father the bike was never rebuilt. When I shine a light into the underside of the piston I see light behind the oil ring so there is a groove back there. Why should that type be replaced?
The upside down ratchet hairpin is probably my fault. I took it off and then put it back to take the picture so I would know how put it back together again...obviously I probably did that wrong :? Thanks for setting me straight! I'm assuming that it would be best to replace the ratchet spring (04.0038) as well as the gearchange return spring (04.0479) underneath it and the rusted washer (04.0135).
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wrecks said:
The long slots weaken the piston. http://www.norvilmotorcycle.co.uk/techtalk34.htm
High revs can cause the piston crown to break off, as several Combat owners experienced before the factory modified the piston design!
Cowboy Don said:
It has been suggested (in the UK NOC Service Notes) that if the engine is kept below 5000 RPM then there's less chance of those early pistons breaking, however, after this time, I wouldn't consider it to be worth the risk knowing the engine damage it might cause.
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wrecks said:
Not all makes of piston require the same running clearance but if the cylinders measure up ok then a new pair of same size pistons (Hepolite, JCC, etc.) should be all that's required (with perhaps a light re-hone to help the new rings bed in).
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I took my cylinder barrels by a local machine shop this morning and the guy there measured the bores for me. They were consistently 73mm +0.0015" at the top, middle, and bottom and in both directions. Seems like pretty good news and he was impressed with how uniform the wear was on them.
Looks like if I follow L.A.B.'s recommendation of replacing the pistons and rings I can get away with standard size and go with something like this JCC/Hastings combo:
http://www.ebay.com/itm/Norton-750-...-HR-/302348734089?vxp=mtr&hash=item4665638e89
Looks like if I follow L.A.B.'s recommendation of replacing the pistons and rings I can get away with standard size and go with something like this JCC/Hastings combo:
http://www.ebay.com/itm/Norton-750-...-HR-/302348734089?vxp=mtr&hash=item4665638e89
N0rt0nelectr@
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wrecks said:
I got a set of Emgo pistons with Hastings rings for around $130 for my 850. They work great with the Hastings rings. I also had the cases and head vapor blasted boy does that make the engine look great.
John in Texas
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I cranked really hard on the 1-1/2 sprocket nut with a really long wrench and it didn't go anywhere. I remembered reading somewhere on one of these threads about applying a little heat so I hit it with a propane torch for less than 30 seconds and it came off like butter. Thanks for the help!
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I got the gear box pulled apart last night. The gears all look pretty good to me, a few small scratches here and there but no major signs of wear. I'm planning to replace the layshaft bearing with the 6203-TB-P63-FAG and will probably order the sleeve gear and 1st gear bushing as well as new springs. I'm hoping the bearings come out pretty easy after throwing the gearbox shell in the oven when my wife isn't home.
Once I'm putting it all back together is there any advice on what kind of oil/lube I should be putting on the parts during re-assembly? It may sit on the shelf for a while prior to the rest of the project getting finished so I figure it shouldn't go together "dry".
Once I'm putting it all back together is there any advice on what kind of oil/lube I should be putting on the parts during re-assembly? It may sit on the shelf for a while prior to the rest of the project getting finished so I figure it shouldn't go together "dry".