cylinder head tubes

[blwilliams]

Cylinder head bolt holes that have broken into the intake port due to porting or CNC.
Any pros and cons about inserting a brass tube into the head bolt hole to prevent vacuum leaks or oil into the port.
I have installed the tubes in the past, but wonder if it is really necessary in a NA application.

[WeingartnerRacing]

I do it I think it helps. However I don’t do it on 3/8 bolt holes because the 3/8 studs fit much tighter in the hole than the standard size

[Brian W]

I use to always sleeve them. But have not in the last 10-12 years.. as long as you put a bit of silicone under the nut/bolt head I have not had any issues in 100's of heads.

[gowest]

Is the clamping integrity affected in a negative manner ? Or possibly cracking issues from a very thin port wall ? Maybe more problematic in iron than aluminum ?

[WeingartnerRacing]

I don’t go all the way down. About .650 from deck. To date no cracking issues that I’m aware of but I use and sell good head castings.

[gowest]

Thanks Eric. I actually had factory iron in my mind and have wondered if they could withstand cutting into the headbolt holes without installing fairly thick tubes, which brings up another question. How does it help to open a wall into a bolt hole and then have the bolt or tube protruding into the port ? Maybe an average area kind of thing ?

[MadBill]

A number of intake CNC programs a nearby shop specializing in Hemis uses break through into the pushrod holes by ~ 0.200" (see 2nd port from left). He says there is only a few CFM impact from the required thin wall brass tubes vs. puttied smooth with no tubes. YRMV.

[GARY C]

I use the tube from these toilet hinge sets, thin wall brass, one tube will do 2 holes, 1/2" diameter.
https://www.acehardware.com/departments ... eats/40418

[steve316]

From a cosmetic stand point the tubes look better. I have done them both ways and could tell no difference.

[gowest]

Well I gather it must be fairly safe to cut into the head bolt hole from a structural standpoint. Thin tubes would probably still add a little bit of strength and cosmetic value. Pushrod tubes weren't so scary since they don't have a clamping force applied. Helpful thread and thanks all responders.

[GARY C]

Well I gather it must be fairly safe to cut into the head bolt hole from a structural standpoint. Thin tubes would probably still add a little bit of strength and cosmetic value. Pushrod tubes weren't so scary since they don't have a clamping force applied. Helpful thread and thanks all responders.

I usually ream down to about a 1/2" before the deck so that the tube has a lip to sit on so the pressure is applied to the deck surface just in case. I ran mine on 12.1 engine with up to 300 shot of nitrous with Fel-Pro blue head gaskets and never had an issue.

[gowest]

Thanks for the personal experience Gary. Always good to gather information, from others experience, that may help to further the search for power.