Starting my top end rebuild, But now I am concerned because of this Options

[Mark Henry]

QUOTE (V6914 @ Jun 28 2005, 11:44 PM)

QUOTE (nebreitling @ Jun 28 2005, 02:58 PM) just make sure that your machine shop flycuts the heads well and insures that the tops of your cylinders are perfectly true.  with that done, there should be no need to lap. Has anyone, besides me, done a close inspection (magnafied inspection) of heads after they have been flycut?

Yep, doesn't matter how good a mill is, you are still cutting material that is harder in some areas that others. The tool will always try to ride over the hard spots.

Still won't use a head gasket, the copper ones are a hair better than the stock gaskets, but in my book that's just a pinch above shit.

[Type 4 Unleashed]

QUOTE (Mark Henry @ Jun 29 2005, 02:48 AM)

QUOTE (V6914 @ Jun 28 2005, 11:44 PM) QUOTE (nebreitling @ Jun 28 2005, 02:58 PM) just make sure that your machine shop flycuts the heads well and insures that the tops of your cylinders are perfectly true.  with that done, there should be no need to lap. Has anyone, besides me, done a close inspection (magnafied inspection) of heads after they have been flycut? Yep, doesn't matter how good a mill is, you are still cutting material that is harder in some areas that others. The tool will always try to ride over the hard spots. Still won't use a head gasket, the copper ones are a HAIR BETTER than the stock gaskets, but in my book that's just a pinch above SHIT.

I, take it that the hair your referring to is a but hair, since you also mentioned shit, but then, a pubic hair is just around the corner. (IMG:http://www.914world.com/bbs2/html/emoticons/happy11.gif)

I, know someone, that is a Certified Aviation Mechanic, he rebuilds aircooled Airplane Engines.

The quality of machine work used on those heads, is art work (VERY EXPENSIVE). Did you know, they use head gaskets. Just think about all that shit flying around above our heads. (IMG:http://www.914world.com/bbs2/html/emoticons/sheeplove.gif)

[Jake Raby]

The issues with the gaskets is that they add ANOTHER expansion rate to the engine that already hass too many dis-similar expansion rates without them.

The stock gasjkets are 3 pieces of .007 thick aluminum and if you expose them to ANY heat, or ever overheat the engine they fall apart, blow and melt parts.

I am going over the process of omitting these gaskets in my new handbook on "Sealing the Type IV engine" and it should be done in 2 weeks and out to the printer...

The methods and practices I go over will keep your heads sealed off and will do so without the gaskets- The right way.

[scruz914]

This thread brings back memories. It has been a long time since I have rebuilt the top end of an aircooled engine.

I vividly remember though lapping cylinders and heads on a few Type Is I rebuilt. You start off with fresh, new, used, whatever, heads and cylinders; spread a real thin smear of lapping compound (you do not need much) on the rim of a cylinder; seat it into the head and work it side to side about 30 degrees around 10 times; rotate 45 degrees from the starting position and do another set of 30 degree side to side reps; repeat all the way around a couple of times. The movement becomes smoother as you continue each set.

Check the contact area between the cylinder rim and the seat area in the head just after the first set and you will see spots where the lapping compound has not touched the head surface. Check it after a couple of sets and you will see a nice clean continuous lap ring where the cylinder rim completely contacts the head surface. Keep each cylinder matched to its lapped head position. Clean, clean, clean the lapping compound off of everything! I don't think you want that stuff hanging around the combustion chamber.

I can't imagine that you take off anything but a tiny fraction of material. I agree with Jake, adding a gasket would just add another element in the works to expand/contract. I vaguely recall that some Type Is called for the gaskets and others didn't (1200 vs. 1500 vs. 1600). I wouldn't be surprised if I got that wrong though.

[cnavarro]

Sorry for resurrecting this old thread, but the "carbon seal" may be a reference to the 3.2 Carrera spec for a .0015-.0035" taper across the sealing surface of the cylinder that causes a gradient in the clamp load when torquing everything down. We use this spec with Nickies on everything but the 930 and later cylinders (since 99% of guys prefer to flame-ring them, so we provide a precision ground surface to start with).

[DBCooper]

If the surfaces are perfectly machined it's true, you don't need to lap. So the catch is have you ever seen "perfectly machined" surfaces? Are you sure? If all machined surfaces were perfect then why would anyone use gaskets anywhere? And even if the surfaces look perfect your eyes aren't good enough to tell if they really are. In fact you won't know if they are or aren't unless you lap them. Absolutely no other way. And it's sensless to worry about or even think you're removing any significant, or even measurable, material by lapping. Think about it, if you have to remove a measurable amount of material to get the machined surfaces to match then they sure weren't "perfectly machined" to begin with, were they?

So it takes you twenty minutes to know that you have a good (they're never perfect) mating surface before it's all reassembled. Remember how bad that "oops" during startup feels? You might not have needed to lap them, but that bad feeling that the "oops" causes is exactly how much it's worth it to make sure it's right as you go along. I have an even better quesiton for you: why NOT?

[brp914]

QUOTE

I have an even better quesiton for you: why NOT?

Because you dont know if the lapped sealing surfaces are co-planar. Or if the cylinder tops are co-planar as mounted in the case. The heads will come from the machinist ready to use, and if not, lapping is not accurate enough to fix it. By lapping, the best you can do is waste your time. Listen to the Cap'n - dont do it.

[LukeD]

Finally I got tierd of waiting for the weather to cool off. I pulled my pass head and here are some pics. The number 2 is on the left and it is the one giving me problems. There were no "head gaskets". I was also having a problem getting the ehaust valve on this cylinder to hold it's adjustment. 60PSI compression test.

[LukeD]

Second

[LukeD]

Recommendations? I know it is probably hard to tell what is wrong in a picture like this but I am completely lost as to what to do with this head.

Luke D

[John]

QUOTE

I am completely lost as to what to do with this head.

Luke,

Here is my free advice:

You were planning on sending off the heads to be rebuilt. Send them off.

They should clean them up for you and will probably fly cut the sealing surfaces (where the cylinders seal to the head).

It looks like #2 cylinder was leaking at the cylinder/head interface (carbon buildup). I would inspect the top portion of that cylinder to make sure it isn't burned or otherwise eroded or damaged.

From doing my own research on this topic, you may want to take all 4 of your cylinders to the machine shop and have all four trued (sealing surfaces squared off with respect to each other) and have them all matched in length (sealing surface to sealing surface). This will allow the newly fly-cut single head to seal up properly to two individual cylinders when the head is torqued down. I would also suggest that the cylinder base gaskets be matched in thickness to insure that the head seals properly on the two individual cylinders.

What I understand is to use the cylinder base gaskets, but omit the cylinder head gaskets.

As far as the lapping goes, I'm unsure.

On one hand, I can understand the concept of making sure that the mating surfaces will be a much better match with each other. On the other hand, can you be sure that you are holding the cylinder perfectly perpendicular to the head as you rotate and lap it into the head.

I agree that the lapping process should not remove much material and to stop the lapping process as soon as the entire sealing surface is a consistant ring.

I would think that just as important would be the cylinder base to case mating surface. While this would not create a compression leak, it could cause an oil leak.



Again, just my 0.02

[LukeD]

Just took the head down to a machine shop. Valve guide on number 2 exhaust is real loose. Needless to say that the valve wasn't seating properly in the seat and the guy doesn't know if he can grind it enough. He is going to call me monday and tell me if it needs a new seat or not. In which case I have to ship to Rimco.


Luke

[rhodyguy]

would one use machinest's dye on both the head and the cly seating surfaces? when the dye is gone from both items you are assured the faces are dead on?

k