1974 Mk2A Project

N0rt0nelectr@ · Jan 7, 2017

I am almost finished with my latest project a 74 Mk 2 A and I have a question.
I have looked and I can't find where the vent off the oil tank goes into the air box.
Looking at the parts breakdown of a Mk3 I can see a grommet but not where it goes into the air box. The 74 parts breakdown doesn't show a thing so I assume there is a supplemental parts book for this model.

grandpaul · Jan 7, 2017

Should be a hole in the top of the airbox on the right side, with a bent pipe and a grommet, also a star washer to hold it from the inside.

It's unique to the Mk IIa, so you won't find it readily online.

kommando · Jan 7, 2017

This is the breather I have on my MK2A which follows GP's writeup.

Pipe exiting bulge on top of oil tank forwards and going under the petrol tank

Pipe entering top of Black plastic box through grommet, never seen a star washer on this pipe inside so will now find one to fit.

N0rt0nelectr@ · Jan 7, 2017

Thank you for your help. Time to pull the tank and check it out.
John in Texas

grandpaul · Jan 7, 2017

FINALLY found the photo in my JPN thread-

Star washer on the outside, to keep the pipe from pushing into the airbox when you try to fit up the hose.

N0rt0nelectr@ · Jan 8, 2017

Most interesting. I pulled the oil tank off, again, and there is no hole where your picture shows it to be. Should be easy enough to put one in.
Wonder if the air box is off a Mk3 or were they the same? When I got the bike it was together and I didn't remove the air box. I do know that installing the air filter is a PIA.

Thank you all for your help,

John in Texas

kommando · Jan 8, 2017

The MK3 box does not have the hole as it has an oil separator and different tube routings. So you need to check which box you have and see what you need to do to convert, as well as drilling the MK2A hole there may be another hole you need to fill in.

Deets55 · Jan 8, 2017

kommando said:
The MK3 box does not have the hole as it has an oil separator and different tube routings. So you need to check which box you have and see what you need to do to convert, as well as drilling the MK2A hole there may be another hole you need to fill in.

Grommet # 38 goes into hole in air box on MkIII's. Might be in a different location on earlier boxes.
Pete

L.A.B. · Jan 8, 2017

N0rt0nelectr@ said:
Most interesting. I pulled the oil tank off, again, and there is no hole where your picture shows it to be. Should be easy enough to put one in.
Wonder if the air box is off a Mk3 or were they the same? When I got the bike it was together and I didn't remove the air box. I do know that installing the air filter is a PIA.

According to the 2/2A parts supplement, the 2A (or perhaps some) had the oil separator, so the hole could be in a different location.

Mk3 airbox:

kommando · Jan 8, 2017

My MK2A is 4103XX, and does not have the separator so looks like only some MK2A's had the separator, if yours is later than mine and does not have the hole in the non separator position but has the MK3 hole then you need a separator and use the separator hole. If its earlier then drill for non-separator.

Rohan · Jan 8, 2017

kommando said:
My MK2A is 4103XX,

Thats a strange number. !
Typo ?

L.A.B. · Jan 8, 2017

Rohan said:
kommando said:

My MK2A is 4103XX,

Click to expand...

Thats a strange number. !
Typo ?

He meant 3104XX

kommando · Jan 8, 2017

Yep, old age brain fart.

N0rt0nelectr@ · Jan 9, 2017

I will look at my bike again and take the battery out and see if the hole is where your picture shows it to be. This has been an adventure in learning that's for sure. My bike is xxxx1413.

John in Texas

N0rt0nelectr@ · Jan 9, 2017

Well I looked again and no hole in either spot. The air boxes aren't really the same as the MK2 A has the mount for the key switch pop riveted to it. At leas it's an easy fix.

Did get it started after 20 years. Took about 6 kicks to get it running, and about an hour to clean up the oil on the floor. You would have though that the Torrey Canyon had gone aground in my garage. I had re-torqued the head but that doesn't fix a blown head gasket. Maybe that was the reason it had been parked all those years ago. I will pull the head tomorrow and see what is going on. It's an adventure!

John in Texas

L.A.B. · Jan 9, 2017

N0rt0nelectr@ said:
The air boxes aren't really the same as the MK2 A has the mount for the key switch pop riveted to it.

That's also odd, as I think every 2A air box we have seen up to now has had the switch bracket attached by bolts.

B+Bogus said:

kommando · Jan 10, 2017

Mine is as per LAB's pics, screwed on with bolts.

N0rt0nelectr@ · Jan 10, 2017

Mine is bolted on too.
Time to start pulling the head and going after the oil leak. Lucky me.

John in Texas

N0rt0nelectr@ · Jan 11, 2017

Well I pulled the head and found what I was expecting. It looks like the head gasket is blown between the push rod tunnel and the combustion chamber which is no surprise with all the oil that was coming out.
What I didn't expect to find was a divot in the left piston. It doesn't appear that a valve kissed the piston but looks like either a casting flaw which I doubt or for some reason a hot spot on the crown. Going to try and post a picture of two and matbe someone can give me a idea as to what is going on.

John in Texas

N0rt0nelectr@ · Jan 11, 2017

N0rt0nelectr@ said:
Well I pulled the head and found what I was expecting. It looks like the head gasket is blown between the push rod tunnel and the combustion chamber which is no surprise with all the oil that was coming out.
What I didn't expect to find was a divot in the left piston. It doesn't appear that a valve kissed the piston but looks like either a casting flaw which I doubt or for some reason a hot spot on the crown. Going to try and post a picture of two and matbe someone can give me a idea as to what is going on.

John in Texas

Here ae better pictures.

1974 Mk2A Project

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