Mikuni V36 Intake Manifold

Edfury828

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Even though I asked the PO of my
MK-III If he had used locktite on the inner intake manifold bolts, and I explained the reason why it is important, and he said that he did, it appears that he did not. They were only finger tight with no indication of locktite on the threads.

So, the moral of my story is, don't believe what people tell you about important things! If only he had been honest, I would've taken care of it right away. Good thing at least that I cought it when I did!

BTW, does anyone know what the "IS" that is cast into the center of the manifold stands for? Maybe the manufacturer?

I also just found that the "through bolts" which hold the left and right sides of my engine case together were so loose that I lost a little over a quart of oil through the gap between the two sides on a 100 mile ride! The bolts nuts and washers are stainless steel with nylock nuts.

I had assumed that those nylock nuts were holding the case securely, and it didn't leak more than an occasional drop which I couldn't find the source of, until the last ride. When I got home the entire back half of the bike including back tire were coated in oil! Once I put wrenches to the bolts I found some were not even finger tight. They are much tighter now, having employed large double box-end (ring spanner) wrenches. The leak is now completely cured.

You might think the nuts need locktite, even though the nylock design should hold, but being stainless, they really should have anti-sieze on the threads... I'm thinking of trying that and keeping an eye on them. The best cure may be to buy a set of stock nuts and bolts, and properly torque them? Of course, they wouldn't be as shiney!

It could be that the PO overlooked tightening the bolts in the first place? The case may have held together due to a (possible) layer of sealant? I've only put about 250 miles on since purchasing, due to it having a few more problems than I've had time for, so it held for the first 150 miles, plus whatever milage he put on it since it was apart for minor (?) overhaul.

Got tired of fighting the old VM36, now awaiting the arrival of a new replacement. Will tune new one with the reccomended (new) parts from the old one. 🙂
 

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Last edited:
Even though I asked the PO of my
MK-III If he had used locktite on the inner intake manifold bolts, and I explained the reason why it is important, and he said that he did, it appears that he did not. They were only finger tight with no indication of locktite on the threads.

So, the moral of my story is, don't believe what people tell you about important things! If only he had been honest, I would've taken care of it right away. Good thing at least that I cought it when I did!

BTW, does anyone know what the "IS" that is cast into the center of the manifold stands for? Maybe the manufacturer?

I also just found that the "through bolts" which hold the left and right sides of my engine case together were so loose that I lost a little over a quart of oil through the gap between the two sides on a 100 mile ride! The bolts nuts and washers are stainless steel with nylock nuts.

I had assumed that those nylock nuts were holding the case securely, and it didn't leak more than an occasional drop which I couldn't find the source of, until the last ride. When I got home the entire back half of the bike including back tire were coated in oil! Once I put wrenches to the bolts I found some were not even finger tight. They are much tighter now, having employed large double box-end (ring spanner) wrenches. The leak is now completely cured.

You might think the nuts need locktite, even though the nylock design should hold, but being stainless, they really should have anti-sieze on the threads... I'm thinking of trying that and keeping an eye on them. The best cure may be to buy a set of stock nuts and bolts, and properly torque them? Of course, they wouldn't be as shiney!

It could be that the PO overlooked tightening the bolts in the first place? The case may have held together due to a (possible) layer of sealant? I've only put about 250 miles on since purchasing, due to it having a few more problems than I've had time for, so it held for the first 150 miles, plus whatever milage he put on it since it was apart for minor (?) overhaul.

Got tired of fighting the old VM36, now awaiting the arrival of a new replacement. Will tune new one with the reccomended (new) parts from the old one. 🙂
Don’t loctite the engine cradle bolts. Far better to use anti seize and nylocs as that way you can you can feel them far more accurately when checking them.

Sounds like the cradle was powder coated to me? The powder coat crushes resulting in fasteners no longer being tight. Happened to me too !

You caught it in good time, these loose fasteners can cause cracked crank cases.
 
Sounds like a typical used Norton 101 lesson to me.

I would have thought the single Mikuni issue was taken care of long ago. You did ask me about it in a PM. I didn't have a instant fix or satisfactory answer. You may have more problems than the older Mikuni VM36 body if it actually has the recommended parts in it. Could be there are minor overhaul problems with the used engine. As I mentioned in my PM response, I haven't ever installed a single Mikuni on a Norton twin. But given I've put Amal, Mikuni, and Keihin dual carburetion on a Norton twin successfully, installing a single must be close to the easiest thing one could do carburetion wise.

No clue what SI stands for. Maybe Single Intake. If it is actually IS, Ixxx Spares. Putting Spares after a name is or was common in the British bike glory days of the previous century.
 
I would never buy a motorcycle and start riding it without checking it first. Stainless steel bolts might stretch more than high tensile steel bolts. I would never use stainless steel on a motorcycle, cadmium plated fasteners are better than zinc plated, and more authentic. Many of the fasteners on my motorcycle are titanium.
 
I would never buy a motorcycle and start riding it without checking it first. Stainless steel bolts might stretch more than high tensile steel bolts. I would never use stainless steel on a motorcycle, cadmium plated fasteners are better than zinc plated, and more authentic. Many of the fasteners on my motorcycle are titanium.
Show us pics of yur titanium fasteners Al
 
Don’t loctite the engine cradle bolts. Far better to use anti seize and nylocs as that way you can you can feel them far more accurately when checking them.

Sounds like the cradle was powder coated to me? The powder coat crushes resulting in fasteners no longer being tight. Happened to me too !

You caught it in good time, these loose fasteners can cause cracked crank cases.
Thanks Fast Eddie! I overlooked the anti-sieze when tightening...just trying to stop the leak and understand WTF?
I'll get some on the threads soon.

I hadn't thought about a cracked case. Glad that didn't happen!
 
Sounds like a typical used Norton 101 lesson to me.

I would have thought the single Mikuni issue was taken care of long ago. You did ask me about it in a PM. I didn't have a instant fix or satisfactory answer. You may have more problems than the older Mikuni VM36 body if it actually has the recommended parts in it. Could be there are minor overhaul problems with the used engine. As I mentioned in my PM response, I haven't ever installed a single Mikuni on a Norton twin. But given I've put Amal, Mikuni, and Keihin dual carburetion on a Norton twin successfully, installing a single must be close to the easiest thing one could do carburetion wise.

No clue what SI stands for. Maybe Single Intake. If it is actually IS, Ixxx Spares. Putting Spares after a name is or was common in the British bike glory days of the previous century.
The new Mikuni is kind of a Hail Mary! Will put the correct new tuning parts in and see what happens.

Interesting speculation on the SI, thanks!
 
I would never buy a motorcycle and start riding it without checking it first. Stainless steel bolts might stretch more than high tensile steel bolts. I would never use stainless steel on a motorcycle, cadmium plated fasteners are better than zinc plated, and more authentic. Many of the fasteners on my motorcycle are titanium.
This bike has been a learning experience! I still stand by it being good, just needs a little more TLC! When I have nothing more to worry about I'll get some proper nuts and bolts for the case. Meanwhile, will keep an eye on the stainless. :)
 
Including a link to this current thread for posterity;

'MK 111 engine to cradle bolts .' https://www.accessnorton.com/NortonCommando/mk-111-engine-to-cradle-bolts.41121/

Though none of it was directed at me, I thank all who contributed. I learned a lot about my cradle bolts situation. I will look into mine further over this winter to see how my bolts and holes look. Hoping my bolt threads aren't causing trouble in the case!

I also wanted to add that upon receiving my new intake gaskets and comparing to the old ones which I had immediately tossed, I was surprised to see the old ones were some sort of plastic. Maybe phenolic resin?

They were dry, and with the loose intake bolts were very likely causing my intermittant vacuum leak problems. The new gaskets were a soft thin paper like material which said something like Performance Gasket Material on them. I gave them a thin coating of Hylomar and installed the manifold with blue locktite on the bolts.

I also installed my new VM36 with 230 main jet, 40 pilot jet, 33 needle and seat (under brass float arm), 6DH3 needle and P-2 needle jet. This being identical to my NWNO buddy's 850 VM36 set up. The 230 may seem a little lean, but he had good "Color-Tune" results with it. I may try a 240 or 250 later...

I ran my engine until fully warm and after a little bit of rough cold running it settled in pretty good! About an hour later in my cold shed, It fired right up and ran pretty good again!

I'm not trusting it completely yet, still need to do another dead cold start, but hopefully, things will continue in this new found positive direction. I'm feeling pretty good that things are looking up!
 

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I have a mk3 with a 36 mikuni and k&n pancake. Choke on ,starts well but has to be warm before turning it off. Then runs like a switch watch , brown plugs no backfires full power etc. Runs a 35. Main jet. Tried all up and down in the beginning but for my engine it's right. Check All ! Roy
 
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