Which Loctite should I use for precups?

[JosieGallows]

So I'm about to install precups and have the heads machined. Should I use loctite 620,640 or 680 to keep the cups from getting ripped out by the cutting blade. I know 680 and 620 Loctite is "thicker" while 640 is "water thin"

Also 640 only cures on active metals. And the precup is ceramic coated Inconel. But the Iron head should be enough to cure the Loctite I assume. I'll be waiting for about a month to have the heads machined anyways, so it'll be cured.

Need advice on what Loctite to use.

 

[ifrythings]

From what I understand, they don't usually machine the heads with the precups in them cause it will damage the cutting stone the shop uses, I know when I got my engine done they popped out all the cups, machined the head, put the cups back in I believe and measured them and then took each one to the lathe and used that to trim them down as the tooling for a lathe can cut the Inconel easier.

 

[icanfixall]

Nothing should be used to keep the cups in the heads. They are a tight fit to begin with. As for cutting them in the heads.. This is true. Some shops do not have the cutter tool that can do cast iron and inconel at the same time but some shops do have that tool. Why are you cutting the heads anyway. Are you sure the heads needs to be cut??? The min head thickness measured from the top of the valve cover gasket area machined surface to the bottom of the head is 4.795 and the max is 4.805. So you don't have much you can take off and still be in spec. Also the valves MUST be recessed in the heads. The intake valve recession is 0.042 to 0.054 and the exhaust is 0.051 to 0.063.

 

[JosieGallows]

Nothing should be used to keep the cups in the heads. They are a tight fit to begin with. As for cutting them in the heads.. This is true. Some shops do not have the cutter tool that can do cast iron and inconel at the same time but some shops do have that tool. Why are you cutting the heads anyway. Are you sure the heads needs to be cut??? The min head thickness measured from the top of the valve cover gasket area machined surface to the bottom of the head is 4.795 and the max is 4.805. So you don't have much you can take off and still be in spec. Also the valves MUST be recessed in the heads. The intake valve recession is 0.042 to 0.054 and the exhaust is 0.051 to 0.063.

machining to be sure my head isn't warped and to get the cups flush. I know of a shop that does have this cutter, so no biggie. I was told to Loctite them in to prevent the cutter from yanking them out. But not sure if I should use 680 or 640. Maybe a glue expert could chime in on this.

 

[icanfixall]

I have never heard of any glue used to hold the cups in the heads when surfacing them. These cups have a 5 thousands tollerence to fit the heads. Thats above or below the head deck 2 1/2 thousands. No more or no less than that. The cups fit very tight in the heads and no matter what you do. Cut the head and then install and remove the cups to turn them in a lathe. your going to be installing and removing them a few times. Or the shop is going to be doing this. Its important that the shop does not sand the heads with the cups in them on a large belt sander. There is no way that can be done with any accuracy. Don't let some shop do that. It will look like they did a fine job using a belt sander but what it does is not correct. There will be high and low spots because the belt is not the same as a cutter thats true to the surface and cutting.. Same goes for the cylinder deglazing tools. The glaze breaker that the balls on the ends of the wires does a nice looking job but.. Its not cutting ture. It follows all the taper and holes making it look like its cleaned up. Only a 3 or 4 inch stone can clean up a cylinder and prove its true with no low spots or taper.

 

[Ironman03R]

Im with Gary on this one, if it aint broke dont fix it! To check to see is a head is warped all you need is a true straight edge and a feeler gauge.

 

[OLDBULL8]

Head warpage is 0.006 maximum, of course the less the better.

How would they get the precups out if there Loctited in?

 

[JosieGallows]

Head warpage is 0.006 maximum, of course the less the better.

How would they get the precups out if there Loctited in?

Machine the heads with the cups in place..

 

[jaluhn83]

1) I don't think pre cups are ceramic coated - pretty sure they're just Inconel.

2) The machinist that I worked with said the big problem with doing heads with cups in is that they'll come loose and get caught by the cutter.... probably also an issue of having the right cutter for the harder metal.

3) Don't machine them if you don't need to. Extra work and risk that's not worth it.

 

[riotwarrior]

Head surfacing machines that utilize a CUTTING TOOL cannot machine our heads with precups in IMHO, only a GRINDING type of surface mill has that capability and from my experiences the grinding type of surface mill when set up correctly, provides the best surface.

That's just my personal take not that anyone elses doesnt count.

Speaking of that there is one of these in a field near me...

You must be registered for see images attach

Tell me that wouldn't go nice at my place
http://www.artsautomotive.com/publications/5-shop/87-in-house-machine-shop

Ya I'd love to set up that machine here at my place

 

[icanfixall]

Then loctite them in the heads and do it. After all it is your heads and precups. This forum offers advice but does not tell you how or what to spend your money on. Advice is given free here.

 

[riotwarrior]

Then loctite them in the heads and do it. After all it is your heads and precups. This forum offers advice but does not tell you how or what to spend your money on. Advice is given free here.

Truth...and offering advice free to a 16 yo kid he will do what he chooses to do right, even if it's not the best thing to do.

I recall being 16 and boy did I have views that differed from today. Now I listen more and research more than then!

If it sounds good must be right cause someone has done it.

There is no loctite used from factory and no need these are interference fit in the heads. Loctite won't do jack once those get warmed up and the engine running nope, but you may be having a mess from loctite in the cylinder....

You do what you got to do Josie...we'll sit back and watch.

You asked us our opinion we gave it to you and you don't agree with it so deal with it.

I'm done here!

Al

 

[icanfixall]

If you can find a machine shop that has this type surface grinder with a magnetic bed you can grind the heads nicely. I operated a machine like this in the machine shop that had 2 football fields of floor space in it. Right next to this machine we had a smaller Blanchard. It was a 36 inch wheel. My last job on the smaller one was grinding flat my exhaust manifolds. The tuff part was grinding flats on the side so it would fit the vice I used. These are messy grinders but they sure do a true grind.
http://www.ebay.com/itm/60-BLANCHAR...563?pt=LH_DefaultDomain_0&hash=item58a5f72123

 

[typ4]

CBN , Cubic Boron Nitride, cutters are used for this with precups in, or a grinder. CBN is the best according to the shop that did mine years ago. they stake the cups in with 4 punch dimples 2 outside the fire ring, 2 inside.