What you find in strange places

Went for a nice mountain top ride the other day the sun was shining and the norton was running well. In the afternoon the bike decided it would not run well down low but once up in the mid band ran like a song. Now for the story, I decide to check the carby for blockages and finally decided I may have an air leak. The bike is fitted with a 2 into 1 mikuni kit. I decided to start by checking the gasket on the manifold and work forward. I removed the two external socket screws on the manifold and then went to remove the two internal ones. This is where it gets interesting, there was only one screw fitted but where was the second one. Oh there it is, it's sitting down the inlet port rattling against the valve guide and valve stem. Appraently too large to be ingested.

There are a couple of witness marks on the valve stem and I'm hoping these are ok(I do have photos). Compression check was normal and the bike did start first or second kick but once the choke was released it would not idle (this was before I started investigating)

When I removed the screws I noticed that there were no flat or lock washers fitted.
Looking at photos of kits on line it doesn't appear that washers are supplied.

Question for the group, are there any washers fitted, any washers would put the head of the screws way out in the air flow.

What have others done when fitting the manifold.

Cheers
Peter R

No Washers fitted. You should be fine. At least damn lucky!

I myself just snugged them up nice tight and even, thin paper gasket. No lock nor flat washers.

Just a suggestion: YDIYW Clean all threads internal and the SHCS all oil--old gasket-sealer etc.

There should be thick heat isolation gaskets that go on the head first----I use a thin layer of 3-bond sealer on these--both sides. then the manifold -again a thin layer of 3-bond. I use locktite Blue on all 4 of the SHCS---threaded in by hand--finger tight--then an allen wrench to snug them down--evenly as possible--don't overtighten or you may run the risk of warping the manifold and then air leaks. Now---go have a beer and come back to finish up in an hour or two--let the 3-Bond and the locktite set up.
You can if you wish---check the manifold mating surface on a flat piece of glass or surface plate--irregularities can be rubbed down with 220 wet/dry on a flat surface to make it reasonably flat again. No big job.

Dangerous to use washer here for 2 reasons, one all washers type tend to let go more than plain metal to metal seating and the washer would have been ingested into chamber but not before it had its way with intake valve lips seating and guide. Those whose bike have inhaled pieces of carb slide know what you lucked out on. Now must keep looking at the rough runing likely undid something else. ugh.

Thanks guys for your reply,
Yes I have come to the conclusion to clean threads and use some loctite master sealant to hold fast the screws (without washers). I'm sure I've sorted the rhe rough running, without the internal bolt in place there will be a 8mm hole to the outside atmosphere through the bolt thread, I'm sure this will be equivalent to a huge air leak!!!.
I've decided to take the head off and have a closer look at the damage to the valve stem, don't want a valve head to fall off now do I.

Cheers
Peter R

Same thing happened to me years ago. My fastback started to run weak and sounded really rich. Stumbled home and found that one of the intake manifold bolts had fallen out. The intake valve and seat were trashed but I made it home. I now use locktite on the allen bolts for the single carb manifold. They are recessed into the manifold and very hard to secure. Locktite and pray.
Mike

Exact same thing happened to me. On my way to work, which is luckily only about 10 miles. It started like normal that morning and warmed up. I got on the highway and all was fine until I started to let up on the off ramp. It finally just stalled and I was able to coast all the way to work (lucky me again). I trucked it home that night. The next day I took the manifold off and found the allen screw sitting on the valve. Did as thorough of an inspection to the valve as I could, put everything together (with loctite this time) and all has been well since. I'll definitely be routinely checking those two allen screws inside the manifold from now on!

Ben

bluemax said:

Thanks guys for your reply,
Yes I have come to the conclusion to clean threads and use some loctite master sealant to hold fast the screws (without washers). I'm sure I've sorted the rhe rough running, without the internal bolt in place there will be a 8mm hole to the outside atmosphere through the bolt thread, I'm sure this will be equivalent to a huge air leak!!!.
I've decided to take the head off and have a closer look at the damage to the valve stem, don't want a valve head to fall off now do I.

Cheers
Peter R

Click to expand...

Use loctite thread loc on the bolts not the sealant, it will seal the bolt as well and retain a lot better. No heat insulater needed due to rubber adapter, I dont use a gasket and just seal with the loctite gasket sealant,its always scary seeing nuts and bolt after the air filter.

Photos of offending bolt.
Reassembled the manifold and carby with full compliment of bolts and the bike ran like a dream
But still going to pull the head and replace the inlet valve as the scuff marks worry me a bit.

Cheers
PR

I hope you are not planning on re-using that bolt. The threads are gone and will fall out again, even with loctite.

I think you got pretty lucky. When I first learned that single carb manifolds had bolts on the inside it made me glad I had two carbs on my bike. It doesn't come up in Amal arguments but at least they don't injest their own mounting bolts. (Yeah I know they eat their slides instead...sorry I brought it up)

I'm not so sure I would worry about the scar on the valve stem. First I doubt it has any sharp edges to create excess wear on the valve guide. The rise of the valve is a fraction the length of the valve guide so the area where the two come into contact is relatively short. In other words, most of the length of the valve guide is still in contact with unaffected stem. I would be a bit concerned about the valve seat since you can't see it. I would probably make sure the valve is fully closed and then pour in some diesel or similar fluid and let it sit over night. If the fluid doesn't drip through the valve into the cylinder then the seat is still good.

Just something to think about. It is probably impossible to get a measurement on the affected area without a tear down but I doubt you lost very much metal off the stem, probably just polished it up bit.

Russ

Came to the conclusion that stainless is softer than a valve stem so the marks on the stem are most likely polish marks from the stainless screw. The compression check is normal and both cylinders are exactly the same to the pound, so no bent valve or seat damage. No big bit of metal missing from the screw so most likely no bits floating in the cylinder. Refitted the manifold with loctite and re fitted carby. Second kick start as usual and ticked over like clock work. So it looks like I escaped any internal damage. Now to revisit those mountian roads again. It was no fun on those 10mph switchbacks leaning into corner and not sure if the engine would light up when the throtle was opened, you look very foolish falling over in the apex of the corner at 10mph when the engine dies.

Cheers
Peter R

Lucked TF out. Do remember to heat the bolts up fairly well to soften the loctite to remove or its gritty-ness tends to wear away alloy threads which aggravates retaining them down the road. Same thing especially on carb bowl and cap fasteners.