[Caroni]

Arghhhhhh, deleted explicatives!

I am finishing up the porting job on a 2L head that came off a motor I acquired and low and behold the hole in the head where the No. 1 Intake valve guide goes is way oversize. I mean, I can drop a new guide right through it without any resistance. So, what to do now.

I guess first consideration is whether the head is cracked along the guide path. I don't see any cracks in the port or in the spring seat and for it to be that out of spec you'd think a crack would be obvious.

Assuming the head is intact and someone down the line opened up the guide bore too much any ideas as how to deal with it? Would it be easier/better to bore it out a bit more and instal a sleeve or to get some valve guide material and make an oversize guide to go in the oversize bore?

I do have another head but the idea of doing all the work over again.... At least it would come out better learning curve and all that.

Any suggestions from the collective mind would be very useful at this point of utter frustration.

Thanks,

David

 

[Gordon Raymond]

David,
This is easy. First you MUST CONFIRM there is no crack. Then just machine up an oversize guide from 954 bronze.
I had this happen with an old 1300 101 race head. I knocked out the old guides and tossed them (dumb #1). I planned to cut the seats from the new guide centers, but someone had replaced one seat, and cut it from the guide bore. The pilot they had did not fit the guide bore, so they opened it up with a reamer to fit their pilot (dumb #2), and made up an oversize guide that I tossed with the rest. I made up ANOTHER oversize guide and spent some time hand fitting it as I had no plug gauges or inside micrometer small enough to measure the reamed guide bore (dumb#3). I could go on, but you get the idea. Any good machinist can make you an oversize guide, using the "drop-through" as a sample. First, just be sure you have no crack!

 

[180OUT]

As Gordon says, check for a crack. If you don't have a crack, in all likelihood the enlarged hole comes from someone removing (or installing) a guide on a cold head. Always do the drill: freeze the guides, heat the head, and the guides will tap in quite easily.

This company used to provide oversize guides for Alfas. You might drop them a line.

Precision Engine Parts - High Performance & OEM Engine Products

 

[Caroni]

Thank you both, follow up questions in other issue

Gentlemen,

1) Where can I purchase 954 bronze rod, hopefully at a reasonable price. I have a small South Bend lathe and I'm sure I can make the guide myself although I will most likely need to purchase a 9-mm reamer.

2) I understand freezing the guides and heating the head for instal but how does one remove them safely.

I admit I just drove them out cold, bad me, but in looking at the guide bore there is carbon buildup inside the bore that suggests it was that way to begin with. The reason I chose to use this head was because when I was trying to find TDC on the motor there was NO compression on the #1 Cyl and I could feel the "wind" coming from the #1 intake port. So, when I took it apart I noticed lots of carbon build up on the valve faces so I ASSumed that it just needed to be cleaned and reseated but went ahead and spent the time to port the head first. I should have had a clue when because I remember one of the guides coming out ALOT easier than the others at the time it just didn't register as a big problem. Silly me.

3) When I looked at it last night it looks as though the hole is not centered. This is just a quick perception I gained when I looked down at the spring seat and noticed that they each have a slight bevel around the opening and this one shows the bevel eliminated on a portion of the circumference of the hole and complete on the other side. I can take a picture tonight if that is of any assistance. So my first thought is that the hole is not circular but oval at this point. any ideas as to how much room there is for one to set it up on a mill and cut a new, centered, circular opening and then make the guide to fit?

Thank you again for your responses and interest in my problem.

David

 

[Caroni]

I also have some hole gauges so I can check tonight and see of is is significantly out of round as well.

David

 

[Gordon Raymond]

Try McMaster Carr for the 954 bronze. If they do not have it they know who will. It comes in rods. You can even get them big enough to cut valve seats out of them. It is not expensive unless you buy a lot!

 

[bianchi2]

i have drivin' out valve guides cold with no problem, but this is how i do it.. i tapp threads in the valve guides on the combustion chamber side, then put a bolt into the thread i just made on the guide, then with a drift, i tap it out for the spring side.. the threaded guide with the bolt in it, allows me to tap the guide out from the 'inside' of the guide, not hamering away on the guide itself, in that case you can 'mushroom' the guide part that you are hamering on, and as you drive it out, it takes part of the head with it, causeing damage to the head.

 

[Caroni]

Bronze Valve Seats?

Pardon my ignorance but what would be the benefit to a bronze seat? Softer, seals better...??? I'm curious maybe something else to try to make and mess up.


Thanks

 

[Gordon Raymond]

The GTA and other racing heads, as well as many ferrari heads used bronze valve seats. The 954 bronze is hard, almost as hard as steel, but offers much better heat transfer, is easier to remove and install, offers a better initial seal and less adjustment in an engine that is assembled, and taken to the track and raced. They work very well with titanium valves, and with any valve style, damp out some valve bounce.
It is NOT worth doing, just to try it, but should you have a need to replace some seats due to repair or valve recession, replacing them all with 954 bronze is somewhat easier than steel seats, and offers advantages in performance engines.
This is from my experience with OLDER Alfa and Ferrari race engines.

 

[Caroni]

Gordon,

Thanks for the great reply and bit of education. It is quite appreciated.

David

 

[Caroni]

0.040 Oversize!

I checked the guide bore and it is in fact round but it is .040" larger in diameter than all of the rest. Someone must have bored it out at some point. I still wonder about the centricity of the hole. i took a picture of it tonight and will post tomorrow if anyone is interested in commenting on it.

Thank you all for your replies thus far it has been educational and interesting which is one reason I do these crazy things.

David