Crack Inside Intake Manifolds

[mhead]

Hi All,

I removed the carbs on my stock 1991 NT650. I can now see into the intake manifold on both cylinders. I see two valves in both the front cylinder and rear cylinder. There is a ridge of cast aluminum between each pair of valves. Both the front and rear cylinders have a crack in this ridge that runs across the ridge from one intake valve recess to the other. The crack does NOT appear to extend down into the valve seats.

That BOTH cylinders show this crack suggests that it is a common defect. Has anyone else seen the crack? Does the crack cause problems?

Thanks!

[ParcNHawk]

Is it a crack or a line in the casting?

[6]

Is it a crack or a line in the casting?

^^^^^^^
that

Have pics?

[mhead]

Yes, a crack for sure. Visible in both intake manifolds. Crack seems harmless enough since it appears NOT to penetrate into the valve seat area. Intake Manifold Crack.png

[tommy dale]

WOW, looks like a casting flaw. How many miles? Sorry I don't have a solution, but seems concerning to me.

[6]

Yes, a crack for sure. Visible in both intake manifolds. Crack seems harmless enough since it appears NOT to penetrate into the valve seat area. Intake Manifold Crack.png

H.mm...

I don't have a set of heads here, also don't remember seeing that. It's strange it would be on both.

In times like this it's always best to lean on your higher power.


Hordpower to be more specific and less AA.

[Hordpower]

Parting line/shift in the casting. All Hawks have it, some worse than others. Not a crack. Well, 99.9999% not a crack, I've never seen a true crack there, but this one is particularly bad. Usually disappears when ported.

[6]

Hordpower;n963745. Usually disappears when ported.

and there it is..
Don't you love it when the solution comes with an added benefit. Hehe

[JanM]

If there ever was an excuse needed to port your heads...

[rpcraft]

Makes you wonder if in 1991 they were just running the program on fumes and gave zero Ef's about the Hawk production or something?

[Hordpower]

Well, the 1991 heads were a different casting than 88-90. So things should have been better.

Makes you wonder if in 1991 they were just running the program on fumes and gave zero Ef's about the Hawk production or something?

[mhead]

Hordpower.. after prodding with a dental pick it seems the "crack" doesn't go much below the surface. My guess is that this is a flow meet-up. I have experience with plastic injection molding. Slight lines sometimes appear in molded parts when the melted plastic arrives at a point from two directions. So two -surfaces- meet and sometimes don't want to flow together slightly which leaves a line. Maybe this effect can explain the "crack" The "crack" does have a nasty offset look to it however.

In any event I believe the valve seats are un-cracked since if cracked I'm sure the engine would complain and the intake port would be carbonized. Major problems.

So I'm going to ignore this feature and put my carbs back on. I'll be happy if I can just get the Hawk running again.
Thanks for ideas and advice.

[rpcraft]

Hordpower.. after prodding with a dental pick it seems the "crack" doesn't go much below the surface. My guess is that this is a flow meet-up. I have experience with plastic injection molding. Slight lines sometimes appear in molded parts when the melted plastic arrives at a point from two directions. So two -surfaces- meet and sometimes don't want to flow together slightly which leaves a line. Maybe this effect can explain the "crack" The "crack" does have a nasty offset look to it however.

In any event I believe the valve seats are un-cracked since if cracked I'm sure the engine would complain and the intake port would be carbonized. Major problems.

So I'm going to ignore this feature and put my carbs back on. I'll be happy if I can just get the Hawk running again.
Thanks for ideas and advice.

It's hard to not be able to get a Hawk running. if it is just dirty and in need of intake boots and carbs rebuilt it should go.

[BBBROS]

I checked my Mark2
The rear is clean and the front has a parting line
Doesn't seem like crack

rear.jpg

front.jpg

mk2.jpg