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Author Topic: Exhaust smoking at head  (Read 736 times)

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AgentX

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Reply #15 on: August 25, 2018, 02:14:27 pm
Loose valve guide.  Through the exhaust port,  I can see it moving along with the valve.


AgentX

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Reply #16 on: August 25, 2018, 03:27:57 pm
That may explain why the oil was only in the port and not in the chamber too.


Adrian II

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Reply #17 on: August 25, 2018, 04:18:20 pm
Oh well. Oversize guide time, could be worse!

A.
Grumpy Brit still seeking 500 AVL Bullet perfection! Will let you know if I get anywhere near...


ace.cafe

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Reply #18 on: August 27, 2018, 11:41:49 pm
Those are custom made guides. You will need to copy the shape on new guide stock on a lathe. Just add the extra needed thickness to the shank O.D. to fit the head. Remember to make a few thou interference fit into the head because of alloy expansion of the hole when hot.
Ream the guide to 1.5 thou clearance for valve to guide.

I can't make any right now because the shop had a fire, and I have no access to any machines.


Arizoni

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Reply #19 on: August 28, 2018, 04:44:40 pm
Rather than making a new guide from scratch, assuming the valve stem to guide clearance is about .0015-.0020, it might be a good idea to look into the idea of plating up the outside of the guide to increase its size.

Ideally a nickle or chrome plate would be used but if the guide is only a couple thousandths smaller than what it needs to be, a simple copper plating would work.

Copper plating is relatively low cost and it shouldn't require machining the outside of the guide undersize prior to plating. Just a thin coating of a couple of thousandths (.002-.003?) thickness of copper per surface is all that is required.
(Nickle or chrome plating needs a copper undercoat and the combined thickness of the undercoat plus the top coat can amount to several thousandths per surface.  For that reason, often the basic  part needs to be machined further undersize before the plating can be done.)

Getting the guide copper plated isn't a job for the shadetree mechanic but almost anyplace that does plating will have the ability to do copper plating.

The only thing to remember about using copper plating is, it is a soft material so it won't like being pressed into the cylinder head if the head is at room temperature.
Heating the cylinder head to 300-350 degrees F (149-177 degrees C) in an oven and chilling the guild in a refrigerator ice box will greatly reduce the interference so just a light tapping with a mallet should seat the guide fairly easily while leaving enough copper plating to maintain the press fit.
Jim
2011 G5 Deluxe
1999 Miata 10th Anniversary


AgentX

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Reply #20 on: August 28, 2018, 07:18:38 pm
Those are custom made guides. You will need to copy the shape on new guide stock on a lathe. Just add the extra needed thickness to the shank O.D. to fit the head. Remember to make a few thou interference fit into the head because of alloy expansion of the hole when hot.
Ream the guide to 1.5 thou clearance for valve to guide.

I can't make any right now because the shop had a fire, and I have no access to any machines.

Chumma's got the head now...


AgentX

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Reply #21 on: September 21, 2018, 10:06:33 pm
Apparently, the guide was in pretty bad shape.  Chumma's working with a machinist to fab up a new one.


ace.cafe

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Reply #22 on: September 22, 2018, 10:17:33 am
I spoke with him about it.
It will be no problem taking care of it.
 :)