K100 Head - To Plug or to Tap
Turbo Mini Forums

I'm about to start dry decking my block for the K100 head before it goes to the machine shop.

I was planning on drilling and tapping the block either 1/4" or 3/8" BSP Taper thread and screwing in some solid BSPT iron plugs, good and tight.

The SC build manual talks about pressing in plugs with an interferance fit.

I'm not particularly happy with the interferance fit because some of the plugs have to be drilled for the new head studs.

What has anyone else done?

Edited by Paul S on 8th Jan, 2008.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I don't like the idea of having the not total contact of a thread there so i would plug,

and would make sure that the plug went all the way to the bottom of its hole. ie with a drill shaped point on the end.

the other alternative is to weld whatever is used into the block.

I'm not concerned with the thread sealing. After all, taper thread plugs are used to seal high pressure water, oil and steam systems.

But I'm not convinced that an interence fit on a parallel plug is enough to help hold a head stud in place.

Problem with the threaded plugs is the tooling costs. The cost of the drills and taps soon add up.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I assume the problem area you are refering to are for the holes in the back of the block which use to be for the water gallary. I drilled and tapped these out. The problem here is the deck is so thin, and we can't make sure the plug goes to the bottom of the hole as it is in the water jacket so would need to be about 200mm long each.

The push rod holes I simply reemed them out and made them an interferance fit.

Team Racing

Thanks, Jimster.

I think I'll do the same. It will be a lot cheaper as all the holes except the pushrod holes on the 998 can be tapped 1/4" BSPT.

What sort of "interference" do you recommend?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

this is prob a really stupid q , but why does one need to block the pushrod holes ? doesnt the gasket do that ?

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Good point.

One would expect that wouldn't one :)

EDIT: Actually there is a water jacket passage in the head in the area of the pushrod holes. I'm not sure that I would want to rely on a thin bit of gasket holding the water pressure.

If you use the bike head gasket, then there would be a big water leak into the gearbox!

Edited by Paul S on 8th Jan, 2008.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

ah i see .thank you paul .

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Drill and tap, i used a loctite 648 then to seal and lock them in. Its good up to 175 degrees and will stick most things. I hope mine will stay together its serious enough stuff.

Ahhh,

I was only thinking in terms of the head stud holes,


When I had the centre brass plug in a 5 port head loose its interferance fit and sink (overlaps the fire ring so caused the gasket to fail) I was recomended to tap and plug it, it left a void due to the thread so i ended up using a 7 deg taper cutter to give a tapered hole machined bung with a 7 deg taper heated the head, chilled the plug and pressed it in using a vice and some locktite, the got it skimmed flat.

The void it leaves is minimal, i used cast iron bar to make sure that the thermal expansion rates were constant.

I decided to tap the head stud and waterway holes and ream and plug the pushrod holes.

I ordered some "malleable iron" solid BSPT plugs and got a tap off ebay.

Trouble is that the plugs have turned out to be zinc plated steel rather than iron. I'm having trouble getting the supplier to change them for what I ordered.

The steel plugs have similar expansion rates to iron but being harder may cause problems in machining.

Any thoughts?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I can see where you're coming from re the maching - i certainly wouldn't be fussed as regards the different expansion rates though.

Are they zinc-coated 'putty steel' or zinc-coated 8620 - I guess that would make the descision easier? If a pretty soft steel, then they'll be fine as you'll no doubt be drilling your block on a sturdy radial-arm or similar piece of equipment?

Yes, I'll be using a milling machine to drill the new stud holes.

I was thinking as much about the facing of the deck and the potential for the steel to end up very slightly proud of the surrounding iron.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."