Fly cutter for Bridgeport

Machine Shop
#1

Do we have a fly cutter for the Bridgeport, something that could cut ~9" wide? I might need to skim my little 4cylinder head for my mini after overheating and blowing the head gasket. If I do, I’d like to try my hand at skimming the head myself if I could get it clamped down and leveled out. If not, I’ll find a machine shop to do the work, but at $200 for a skim (Wayne Calvert in Denton), it seems worth trying myself if we have the tools.

Here’s an old photo of the head in question, I haven’t looked at the head in its current condition yet. Flat, small, and maybe 6.5" across.

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original_941c9be9-cbeb-47e6-8bb6-a780c9e35d95_PXL_20220315_0023274081351×937 286 KB

#2

We do not.

#3

Tooling for this would run well above $200. Cutting tool plus inserts. Also fixturing the head on the Bridgeport to keep everything orthogonal for the whole process would probably be a major pain. $200 seems like a lot until you consider time saved and the risk of damaging the head in a diy setup. Planing the head will raise the compression ratio - something to keep in mind. Any idea what caused the overheating?

#4

The radiator fins are clogged up from oil/coolant leaks (the water pump failed on the way back from Virginia and was dripping from the weep hole, but has since been replaced prior to overheat). The mixture of oil and coolant was blown onto the radiator in a fine mist by the fan and it collected then filled a lot of the fins with the gummy mixture. I’ll need to clean those out as well as the head work.

$200 is excessive for a head skim when I’ve got friends in Salt Lake that get charged $50, and last time I had it done was maybe $75 in Haltom City (considering calling them up again, but no way to get the head there since the Mini is my only car). The head is completely flat on the top and bottom faces, so it would be a matter of securing it. It isn’t angled at all. The head is made of iron, not steel or aluminum (worth mentioning, but not sure what that would do for cutting characteristics). It’s small enough that I also thought that maybe a boring fixture might do an adequate job of cutting, like in this video ✂️ Using a boring bar for head surfacing - YouTube

Current idea is to bring the head in and use a dial indicator on the Bridgeport to check for flat. Other idea is to get some plastigage and clamp the head back down on the block to torque specs and look for obvious high/low spots based on the amount of squish, just like in a crank bearing when reading for correct clearance.

Open to ideas <3

#5

UPS the head to Salt Lake City or Favor it to Haltom City. Not sure when you had your last machine work done, but everything has gone way up across the board. Junk yard?

If this is your first rodeo milling a head, are you really sure you want learn on your only mode of transportation to save $125? That is assuming we had the tooling, which we don’t.

#6

It sounds like you need to start with cleaning the head, followed with a good machinists straight edge, and a feeler gauge or two around your go/no go dimension. Maybe a gentle rest on a surface plate to test for twist, but running the straight edge through several lines should catch twist as well.

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#7

If you’re very fussy about tramming in the head, checking inserts on the shell mill, and setting it up, maybe you could get what you need by taking multiple passes with the shell mill? I know it’s not ‘proper’ but I don’t think you’re looking for tenths here.

You ought to be able to check for flatness with either the Bridgeport or the surface plate that’s covered in plywood by the cold saw. I would go for the surface plate if only because I don’t often have a use for it.

The Bridgeport also has some slop in the table, if you stick an indicator on it and run the table from right to left you’ll notice a few thou change over the full travel. You should check how it changes over the length of the head and make sure it won’t be an issue. Maybe someone who uses it more often would know if I’m just being overly cautious or not.

#8

You can’t really check for flatness using an indicator on the Bridgeport, because at its age, you aren’t really certain if you are measuring the head, or deflection of the table due to worn ways.

Also on play, there is usually a minimum surface texture that the head gaskets need. Making the surfaces too smooth can result in early gasket failures.

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#9

I know it’s a crazy idea, but the way I approach problems usually involves trying to see if it’s something I can learn if the barrier to entry isn’t too high. In this case, yea, the risk probably does outweigh the benefit of savings on the bill. It’s been a couple of years since I had machining done, and that’s a fair point about the rising cost of labor.

That’s why I’m avoiding the sandpaper and glass technique, figured milling might be better, but the deflection issue is totally valid.

I don’t want to mess up the surface potentially, but if we have a machinist’s straight edges at DMS, I’ll definitely give it a go. I’ve got a painter’s straight edge but it’s got flex in it and definitely not “true”.

If the overall cost of repair has gone up then it’s just a pill I’ll have to swallow to get it done. I’d rather have these conversations in the open instead of blindly accepting what is potentially a “go away” price from a machine shop for my small job. I’ll get more quotes and decide from there.

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#10

We do not have a machined straight edge. However if you get your head mating surfaces incredibly clean, you can blue it on our granite surface plate. If you were to go this route, you will need help to make absolute certain that you do not drop the head on the granite. This will at least tell you if its flat…

I will re-emphasize that you will need help. I don’t know about you, but I would you rather not be “That guy who screwed up our granite”

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#11

Starting to have flashbacks to my Pinto Ford 2.0L days. Pull head, clean surface down to bear metal. Get a straight edge and feeler gauge. Go length wise - edge, center, other edge. Use feeler gauge to check between straight edge and head surface at multiple points. Do the diagonals also. Ideally block deck should be checked separately. Works reasonably well if surface hasn’t been o-ringed.

There are shops here in the Dallas area. IIRC someone posted out here on the forum looking for one. Forum search might yield something useful. “Original” Mini group in Dallas?

Understand the luv for the Mini. Might want to budget in a parts chasing / daily driver. I remember friends w/ modified muscle cars doing this after the Arab oil embargo. Commuter car versus weekend warrior. Fun times.

#12

Yeah, I’m actively working on saving for a modern daily. I gave my ex the corolla when we split since I work from home and she doesn’t. Hopefully, next year I’ll be in a better position for that.

Consent is key. Thank you for that, I would have steered clear for that exact fear! I definitely don’t want to be that guy. I’ll bring a friend and make sure that we’re especially careful and that it’s perfectly clean

#13

Flatness and squareness as (@kbraby points out) of heads are generally checked with precision straight edges and feeler gauges. Before and after - low tech but effective.

  • Parallel to the long edges in multiple places
  • Diagonally across corners
  • Perpendicular to length at multiple places
    Using the feeler gauges you’ll get where the high and low spots are. The head gasket can take of a bit of the difference. The Engine manual should give what the maximum allow gaps/high spots are. If they are within the allowable limits, I’d suggest leaving it alone unless you are going to have a machine shop do it.

Also remember, that the more you remove the closer the valves when opening are going to be to the pistons. If it is an interference fit engine this could really be a problem if more than few thousandths. If non-interference make sure you know the clearance isn’t reduced so that it can now touch.

@artg_dms point of effect on compression: clean the head really well especially the chambers. CC them as precisely as possible (don’t use water, it doesn’t “wet” to iron surfaces very well and will form a pronounced meniscus at edges. Use some sort solvent - check manuals). Record for each cylinder after machining. This will allow you to calculate the compression of each cylinder. Depending on change you may have to use higher octane fuel and change ignition timing slightly.

Without fixtures, the cost of 5+ new inserts for cast iron need to be added to the cost if using a shell. After you deduct that cost plus any fixture tooling will be what you saving vs trashing the cost of a head replacement.

There are three operations I’d always send out:

  • Head/Block surfacing/decking
  • Line boring for the crank
  • Oversize cylinder boring

Rest of work is much more tolerant of being off or being able to make it right. But those above are highly dependent proper tooling/fixturing and a machine with very little runout. I would not put our knee mills in that last category.

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#14

How long is the head diagonally?

I have a set of 12, 24, and 36 inch straight edges, allegedly good to 0.0002 per 12 inch that I won’t let out of my sight, but if the timing works out, I might be able to bring up for an hour.

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#15

I managed to get the block and head cleaned up and both of them came out perfectly flat and in great condition. One new head gasket installed and it’s back on the road. I just need to bring the Mini in to clean the radiator to solve the overheating issue. In the meantime I’m running my heater :sweat_smile:

Crisis averted thankfully

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