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Author Topic: FYI new Metros and glowplugs and gaskets and barbarian machining  (Read 5651 times)

biobill

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  My '06 Metro 6/1 was getting reluctant to start when the temps got under 30F. Found out about glowplugs (thanks Bruce ) on this forum and ordered up one from Utterpower hoping for a 10 minute fix to my problem. It arived quickly and looked to be a nice piece of work. Unfortunately Metro changed their head design recently and the standard plug protruded much too far into the precombustion chamber. George had heard of this and offered a refund if I wanted, and said that some had been successfully installed by making a spacer to shim it out to the correct depth. So much for the 10 minute fix.
  A quick check with a caliper convinced me that there would not be any handy spacer material in my scrap inventory and machine shops are a long ways away. Also, the top end hadn't been checked on this engine and I'd read some pretty low compression ratio numbers in this forum and maybe this was an opportunity to improve things a bit. More fun than cleaning house anyhow.
  Pulled the head . The casting was much nicer than my older Metro (part of the "redesign"?) clean, generous cooling passages, everything lined up nicely. Checked the deck height -.070"-damn. Pulled the barrel and found 2 1/2 gaskets! A .007 gasket had been torn almost perfectly in half perpendicular to the crank. (Has anyone seen that before? Please tell me it's not the way they true their block decks.) The stud holes were cut to the outside and I'm guessing (hoping) that they use tear aways during assembly and the lunch whistle blew at the wrong time.
  Measured the head volumes and did the math and came up with a CR of just over 14:1. Dismal. The spherical cut in the stock plug held 5.5 cc's and if it was eliminated, it would still only bring me up to just under 16:1. Decided to reduce the plugs volume but keep a spherical shape. A 2 inch circle fit nicely in the stock plugs cut, I'd use a 3 1/2 inch circle for my sphere (or about the size of a wornout 4 1/2 inch grinding disk).

  Real machinists should find another thread at this point. Everyone else should understand that YOU SHOULD NOT DO THIS! At least not this way.

  I needed to spin the plug to make a reasonably accurate cut, the idea being that I'm going to take the Utterpower plug and cut it back to the dimensions of the stock plug and then give it a shallow spherical face. I am without a lathe so the trusty drillpress and a mandrel seemed like the way to go. The Utterpower glowplug setup uses a CS valve plug that has been machined to accept a glowplug. Because the glowplug sits deep in the plug they use a brass rod that screws onto the GP as an electrical extension. A fiber composition plug fits snugly over the brass rod and into the bore hole of the plug. A nice setup. Probably not designed to be a mandrel though. Tiny threads, soft metal. I knew that. What we need is a 12X1.25 bolt to go in the GP hole but, alas, that's not real common and the nearest one is probably as far away as the machine shop. So..if we're real careful, (and we were) and it spins reasonably true (and it did) maybe it will work (got lucky). Took an old glow plug that I'd saved for just such an occasion ::), cut the nose off and reassembled the plug and extension. Chucked it in the drill press and ran the table up til it was just touching to try and stabllize things as much as possible. Spun it slow and gently put a hacksaw to a line I'd made and, by golly,it worked. Cut the last bit by hand to avoid binding. Got the table out of the way and held the angle grinder, precicely positioned by eye, with the edge of the wheel to the center of the plug. Carved a lovely sphere. Polished it with a stone and the darn thing looks fine. Capacity is just over 1 cc so thats a reduction of 4.5cc which puts the CR at 14.86:1 Maybe I screwed up the math or measurment someplace.
  Anyhow, engine runs well, but then it did before too. Maybe a little less smoke. The glowplug is great, first compression stroke fires.
                                             Bill
Off grid since 1990
6/1 Metro DI living in basement, cogen
6/1 Metro IDI running barn & biodiesel processer
VW 1.6 diesels all over the place
Isuzu Boxtruck, Ford Backhoe, all running on biodiesel
Needs diesel lawnmower & chainsaw

mobile_bob

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Re: FYI new Metros and glowplugs and gaskets and barbarian machining
« Reply #1 on: October 26, 2006, 06:22:50 AM »
that half gasket seems to illicit much debate and upset amongst a few that have found it.

i for one am not alarmed by it! if a half gskt brings things into alignment, then why not use it?
certainly far cheaper than having to remachine parts to get them right,

i know this statement makes the purist cringe, but it is a fact of life

much rather have an engine that was trued with half gskts, than one that was thrown together needing the half gskt to correct alignments.
at least with the half gskt one has a clue as to what should be checked and corrected by machine work if you feel the need to do so.

btw, i like your creative use of the drill press, hacksaw and grinder :)

bob g
otherpower.com, microcogen.info, practicalmachinist.com
(useful forums), utterpower.com for all sorts of diy info

Geno

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Re: FYI new Metros and glowplugs and gaskets and barbarian machining
« Reply #2 on: October 26, 2006, 11:25:39 AM »
Hi Bill, that sounds like a nice bit of DIY on the plug. As far as the 1/2 gasket is concerned at least someone in India was checking things as the engine was assembled. Whats your squish clearance between the piston and head? You may be able to get some compression there. The first time I did it I didn't put the lead in line with the wrist pin and adjusted to that. A couple weeks ago I did it correctly, came up with .040 and added a gasket.
Thanks, Geno

biobill

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Re: FYI new Metros and glowplugs and gaskets and barbarian machining
« Reply #3 on: October 26, 2006, 03:09:04 PM »
  Oh no Bob! So they do it on purpose huh? Well the 1/2 gasket is sitting on my bench with the other one that I removed. I didn't recheck the deck height after I removed the required gaskets. Dumb on hindsight. Do you think a bump check would be conclusive about the need for a shim ? With the lead on the extreme edge of the piston I would guess. Any other ideas for measuring the cylinder/crank relationship without a complete teardown? The idea of an untapered shim really bugs me. If it was .007" out at the edge then, assuming things are straight, it would be .0035" out in the middle. But if it works, then OK. I have to keep reminding myself - it's not a race motor, it's not a race motor....        Appreciate the wisdom, Bill
Off grid since 1990
6/1 Metro DI living in basement, cogen
6/1 Metro IDI running barn & biodiesel processer
VW 1.6 diesels all over the place
Isuzu Boxtruck, Ford Backhoe, all running on biodiesel
Needs diesel lawnmower & chainsaw

xyzer

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Re: FYI new Metros and glowplugs and gaskets and barbarian machining
« Reply #4 on: October 26, 2006, 03:43:38 PM »
Biobill,
Machinists call it a vertical lathe...if it turns you can use it!
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aqmxv

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Re: FYI new Metros and glowplugs and gaskets and barbarian machining
« Reply #5 on: October 27, 2006, 02:44:57 AM »
Biobill,
Machinists call it a vertical lathe...if it turns you can use it!

Back in the day when I was young and poor, I owned an overhead-cam Fiat and was rebuilding the enigne in Shreveport, LA.  The one shop there that had parts for it didn't have any of the valve lash adjustment shim sizes I needed.  The valves and seats had been ground, and so the resulting clearances were all less than they had been before the rebuild.

My solution involved a drill press, grinding wheel and arbor, and using one of the lifter buckets and assorted screws, washers, and nuts bolted to the table as a jig.  Properly arranged, they allowed the bucket to be rotated without slinging it off the drill press table.  The stone and arbor was clamped into the chuck, and the table tilt was adjusted so that the unpolished face of the valve shim was very, very slightly not in plane with the stone.

The result was about a .0005" conical cut surface grinder.  It worked pretty well as long as I kept the STP flowing to keep things cool.  After about three hours' work I had all twelve shims precision adjusted to exactly the middle of the specification range.  The engine ran another 50,000 miles after that, which isn't bad for a Fiat.

Recommended?  No.  But it worked, and if I were in such dire straits with such limited tools again, I'd do it again with confidence.  While the machining process was dodgy, the results were predictable and exact (took about five minutes to remove .001"), and everything was well within its limits.

"If it's stupid and it works, it isn't stupid."
6/1 Metro IDI for home trigen