Plz Clue Me on Precups......

[idi_econoline]

Could have brought this up on my current thread about chuffing, but split it off to a new thread:

Had my heads "fully reconditioned" 1½ yrs ago. I knew what precups do, and that they are made of that magical Inconel alloy. At that time, I was told that 1 of my precups was cracked, and it was replaced with a good used one (!?!) Was told by my now-suspicious machine shop that precups were too expensive to replace with new. Yet, I see discussion on this board that several members do, in fact, replace them. Dubious shop said precups are like $180 apiece? With new heads costing like $700 new?

I was told that I now have cracked precups, due to having run with "bad timing," no indication of whether that means advanced or retarded. I'm guessing that this is heat-related? Due to early ignition? (Was I reading on here that they're ceramic-coated? Is it the ceramic that cracks, then?) Or does the Inconel crack?

School me, gentlemen, before I spend any more money!

 

[OLDBULL8]

I suggest you read this thread, then draw your own conclusions.

http://www.oilburners.net/forums/showthread.php?68363-Which-Loctite-should-I-use-for-precups

 

[riotwarrior]

I posted a crapload of pictures in another thread about precups wanted search for it, you will see what I have if yours are worse then I can sell you some if need be.

There are actually 3 fairly recent precup threads going on the one that Bill above posted about and two others.

Al

http://www.oilburners.net/forums/showthread.php?68251-Pre-Cup-Needed

http://www.oilburners.net/forums/showthread.php?68088-Who-sells-IDI-heads

Hope that helps

 

[idi_econoline]

Thanks, guys. I guess I actually need to look at them, closely, for myself. (Both the other threads, and my precups!)

One newbie question, though: "Knock them out?" How? Stick a screwdriver in the hole?

EDIT: And, if so, the hole on the cylinder side, or the injector hole?

 

[OLDBULL8]

Injector hole.

 

[79jasper]

Did you ever post a pic of your "cracked" precup?


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[idi_econoline]

Not yet, 79jasper. The guy from the dubious head shop pointed to one he said was cracked, while it was at the vacuum tester. He didn't let me in close enough to look.

Will look at this head (and my other head) closer, and get out my best camera, which does macro!

BTW, I have 2 other used heads sitting. Will check the precups in those, as well.

Injector hole.

As usual for me, OLDBULL, I actually didn't think the injector hole was the one to use. And, as usual, I stoop corrected.

 

[79jasper]

Oh lord. Lol
Probably not anything wrong with it then.
I thought maybe you had seen some big cracks in it or something.


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[icanfixall]

The cups can be removed 2 different ways. I recall a tool that has a slide hammer end and a hook on the other end. the hook fits in the throat and then its knocked out. the other way is a brass rod thru the injector hole. I believe its a 1/4 inch round brass rod that works. Best to buy a stick of the brass rod. Pounding them out does bend the rod sometimes.

 

[idi_econoline]

Ah, that sounds better, Gary. I thought a steel pin punch through the injector hole sounded too scary.

OK, super busy day coming today, in a very busy week. Will be checking mine out, up close and personal, time permitting.

BTW, Riotwarrior Al's pics of his illustrate very well what to look for.

NEWBIE CONFESSION: I thought that "88" stamp was some super-special RIVET that held the precup in..... yupyup.

 

[typ4]

3/8 inch long is the standard acceptable crack length before replacement. I have yet to see any that arent cracked a little.

 

[icanfixall]

These cups have a very tight fit. That ring around the edge is the fit plus the bottom area fits in the bottom of the head. there is a large air gap around the sides to keep the heat from transferring to the head. I'm sure most of this information is a surprise to some. Finally these cups have an alignment pin too so they can be installed correctly only one way.