Plastic inlet manifolds

[T3 ANDY]

One of the alloy manifolds on the t3 had cracked. So i thought a set of these one piece plastic manifolds should be a good move,
As the alloy ones seemed hard to get. I needed to drill out the holes to 8mm to fit the studs. The problem is that if you drill out to 8mm
there is no metal insert left and that is a huge problem. I made some washers to help distribute the load but this was not enough to stop
the plastic from slowly deforming. You just could not tighten the nuts as each time you came back from a ride they were loose. In the end
the whole manifold had gone out of round. You would think a inlet manifold should be made of better material. I will now make some out
of solid alloy.

 

[baloo]

Do you think inserting helicoils into the head and using the smaller diameter bolts (not 8mm) would work?
Or do you think the plastic manifold just is not good?
Thanks.

 

[scottmastrocinque]

You can easily use the plastic ones. You just need to obtain some hobby grade brass tubing, and cut screw sleeves from this tubing, long enough that the clamping holding force of the retaining screw, is being borne by the brass tubing and not the plastic. Problem solved.

 

[T3 ANDY]

One of the alloy manifolds on the t3 had cracked. So i thought a set of these one piece plastic manifolds should be a good move,
As the alloy ones seemed hard to get. I needed to drill out the holes to 8mm to fit the studs. The problem is that if you drill out to 8mm
there is no metal insert left and that is a huge problem. I made some washers to help distribute the load but this was not enough to stop
the plastic from slowly deforming. You just could not tighten the nuts as each time you came back from a ride they were loose. In the end
the whole manifold had gone out of round. You would think a inlet manifold should be made of better material. I will now make some out
of solid alloy.

You can easily use the plastic ones. You just need to obtain some hobby grade brass tubing, and cut screw sleeves from this tubing, long enough that the clamping holding force of the retaining screw, is being borne by the brass tubing and not the plastic. Problem solved.

View attachment 33234

 

[T3 ANDY]

I think your right its the inner sleeve that takes all the load. I will machine up some sleeves.

 

[scottmastrocinque]

Good Luck!

I’m fairly confident that once you transfer the load to the brass sleeve, the plastic will retain its shape no worries.