My ‘72 engine let go in a big way the other day. The cylinder head is still good, but that’s about it. In the 212- - - serial number range. Before I start searching on Ebay and the like, does anyone here have any parts for sale?Maybe an engine? I’m located in New Hampshire, USA. Thanks.
Catastrophic engine kaboom
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concours
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Where in NH?
marshg246
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PM Sent
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You didn't have a check valve on the suction side of the oil line by chance? My first thought.
I've seen it happen. I take it the con rod punched a hole in the crankcase and took out everything else below the head?
I'm very Curious what caused the blow up?
I've seen it happen. I take it the con rod punched a hole in the crankcase and took out everything else below the head?
I'm very Curious what caused the blow up?
I sure would like to know why it happened also. Not a Combat motor, 10-72 production. Doing about 50 mph, let off throttle, going down steep hill, pulled in clutch as soon as I heard/felt the calamity. Was able to coast the half mile to my driveway. I guess it could have been worse, might have locked up the rear wheel and spit me into the pucker brush. I was so hoping to ride it to the INOA rally next month. My first Commando since I sold my ‘68 in the late ‘80s
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Hello; I am on the other coast but I have the motor, transmission and frame of a 72 Combat, matching numbers and Maryland title. If you are interested please respond to northernnortonnut@gmail.com Mark
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Had the bike been running properly over the months/years until this occurred? Lack of oil (or pressure) would be the usual suspect. Did you have someone do engine or oil pump-related work on it between the time it was running normally and the grenade conversion?
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212xxx should be too late to have had either.
marshg246
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Agreed - "should be"
As best I can tell:
In theory the non-slotted pistons started at 204166 but that does not mean that dealers no longer had stock. Almost every Combat engine I've taken apart had them regardless of serial number. Since his is non-Combat he is less likely to have had them even though the interim pistons were for Combat but approved for non-Combat. I have records on a couple: 206xxx, and 220xxx had slotted pistons and they were standard size.
N68 Dated Oct 71, 1st bearing upgrade
N2/06 Dated July 72, 2nd bearing upgrade
N2/09 Starting from 211891 and dated Aug 72, 3rd bearing upgrade
N2/10 Dated Jan 73, 4th and final bearing upgrade.
"Original" may have been wrong, but easily not 3rd or 4th upgrade - dealer stock again.
212xxx Oct/Nov 72 so should have left the factory with the 3rd bearing upgrade but definitely not the last.
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My combat dropped a valve about 25yrs ago.
It was traced to a combination of factors. The bike was shipped by Norton with a oil dipstick that was too short so the oil level in the tank was too high. Also, the bike still had the stock airbox with the tank breather that blew vapor into the right cylinder. I was riding rather hard one late afternoon on the interstate, stopped at a rest area on the top of a mountain for a bio break and took off again. On the downhill the engine went bang and the right exhaust valve came though the case.
On disassembly it was determined that the oil vapor from the tank was coating the right valve stem for quite a while. The surmise was that on the brief stop at the rest area, the exhaust valve was stopped off of the seat so did not cool down properly. On the downhill, the valve stuck open from the oil residue and heat and the piston knocked the head off of the valve, causing the catastrophic failure. This was a late commando combat sn 209*** and several knowledgable commenters said this was a known phenomena in the early days with stock airboxes and original oil cap dipsticks. Note that this had little to do with the bike being a combat.
Just food for thought. I think there are too many assumptions that combats go bang just because of compression and cams.
It was traced to a combination of factors. The bike was shipped by Norton with a oil dipstick that was too short so the oil level in the tank was too high. Also, the bike still had the stock airbox with the tank breather that blew vapor into the right cylinder. I was riding rather hard one late afternoon on the interstate, stopped at a rest area on the top of a mountain for a bio break and took off again. On the downhill the engine went bang and the right exhaust valve came though the case.
On disassembly it was determined that the oil vapor from the tank was coating the right valve stem for quite a while. The surmise was that on the brief stop at the rest area, the exhaust valve was stopped off of the seat so did not cool down properly. On the downhill, the valve stuck open from the oil residue and heat and the piston knocked the head off of the valve, causing the catastrophic failure. This was a late commando combat sn 209*** and several knowledgable commenters said this was a known phenomena in the early days with stock airboxes and original oil cap dipsticks. Note that this had little to do with the bike being a combat.
Just food for thought. I think there are too many assumptions that combats go bang just because of compression and cams.
Claremont.
Yep, blew a hole in the timing side case just behind the cylinders and locked up.
Bored 20 over last year and new pistons and rings.
marshg246
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Is the conrod on the timing side broken?
marshg246
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OK, that will stop a lot of the guessing. Has anything been done inside the crankcases since you've owned it?
