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+--- Thread: Snapped plug, damaged thread (/showthread.php?tid=4345)
Snapped plug, damaged thread - fcp - 02-11-2013
In the process of rebuilding a 606.962 to go in my W460 g class which I plan to drive in Tuareg rally next year.
I am shooting for 350-400HP with Myna pump and Holset HX35 (actually modified HX35 made by Compressor Racing in the UK).
I have removed the cylinder head which I was planning to have ported here in the UK too, but had 2 stuck plugs which snapped.
While drilling out one of the plugs the tip wandered away from central line by around 1mm because of electrode (also snapped off so I have been using a carbide drill to cut this too) - just enough to remove thread to one side (pics attached).
I stopped drilling as soon as I realised this and have not yet drilled the full depth of the thread (1-3mm to go I think).
In a regular road vehicle, I would not think twice about having the plug thread drilled out and use time-sert to repair ... I am hesitating though because it isn't a regular road vehicle and...
1 It will be will be under more duress because of additional performance
2. I cannot afford to be broken down several hundred miles into a race in the desert for something that could have been avoided!
3. Porting work on head is expensive - I don't want to spend money on this head if it is flawed.
Buying a used head is the alternative, not especially expensive (porting and valve work is more) but I am concerned that I may risk more by this route - my engine is sub 90K miles and in great condition .. who knows what problems another used head may have.
So question is - Perhaps plug is not under as much stress as I think and a time-sert will be just fine?
The other possibilityis to weld and re- drill/ tap. But thermal stresses from welding? Not even sure what head alloy is..
It is also possible I guess that when I finally get the rest of the plu out and re-tap the existing hole the seal will be good.
What would others here do in this situation?
RE: Snapped plug, damaged thread - Simpler=Better - 02-11-2013
Take it to a machine shop. Depending on how the 606 glowplugs seat, you make be able to get away with a slightly recessed hole, then press a new landing in to seal the plug.
Welding is also an option, so long as the oil was baked form the casting prior to welding.
RE: Snapped plug, damaged thread - fcp - 02-12-2013
(02-11-2013, 10:47 PM)Simpler=Better Take it to a machine shop. Depending on how the 606 glowplugs seat, you make be able to get away with a slightly recessed hole, then press a new landing in to seal the plug.
Welding is also an option, so long as the oil was baked form the casting prior to welding.
Re. welding - Could you take a guess at the Alloy? How about problem of thermal stress induced?
I think I'll run it in this PM to a local shop and see what they say about EDM'ind the rest of it out anyway
RE: Snapped plug, damaged thread - Simpler=Better - 02-12-2013
I'm not an aluminum welder, but as I understand you should be able to run a strong filler rod. If it can't be welded, some kind of plug to help with the damaged section might work.
You might be able to find a similar tipped glowplug with larger threads, and machine the head to accept a different GP (at least on that cylinder)
Are most of the threads OK? as in, 3/4 of the diameter? The machine shop should be able to answer your question. Make sure they understand that you have extremely high compression (22:1) AND you will be boosting on top of that.
I have no idea what the head material is. The classic center might be able to help you out (is a 606 considered classic these days?)
RE: Snapped plug, damaged thread - fcp - 02-12-2013
Their take - too risky to re-machine like this :-( Given use and low cost of new head, they advise against Time-sert/ welding approaches.
F**CK!
What a dum-f***king stupid mistake to make... I am an idiot. A waste of a low mileage head.So options... new head is easy to obtain, but what are the risks... ?
How much does it matter that the head is from different engine.. wear etc..
Should I proceed by using new head + cams that it comes with or use existing cams (being reground anyway).
What else should I do as a precaution? Seals, guides?
RE: Snapped plug, damaged thread - Simpler=Better - 02-12-2013
Shit happens, every once in a while I really screw myself when I get saw happy.
The good news is, that you have a junk head to saw up in 1/2" increments, and post pictures along the way. That way we can all see how thick the castings are and where we can safely remove material when hunting for performance
With any head, while it's off you should check:
flatness
pressure test (for cracks)
valve guide wear
valve seating (checked with alcohol/acetone, etc.)
For performance:
port the ports
get a whatever number angle valve job done (a shop can figure this out based on space)
CC the chambers-don't know how much the 606 is recessed, I know these heads don't have a ton of room.
ream your prechambers-this one is controversial, so do it at your own risk.
Also, this may help you out:
http://www.mye28.com/viewtopic.php?t=97370
RE: Snapped plug, damaged thread - fcp - 02-12-2013
(02-12-2013, 03:57 PM)Simpler=Better Shit happens, every once in a while I really screw myself when I get saw happy.
The good news is, that you have a junk head to saw up in 1/2" increments, and post pictures along the way. That way we can all see how thick the castings are and where we can safely remove material when hunting for performance
You know what - I'll do that.. There are not too many ways to pay forward the help I get here and elsewhere so why not :-)
Which way do you want it bisected? laterally or crossways?
I do need to find a new head first
RE: Snapped plug, damaged thread - Simpler=Better - 02-12-2013
In the short direction, so we can see all the port wall thicknesses. Right now people are shooting in the dark
RE: Snapped plug, damaged thread - Joaquin Suave - 02-13-2013
I have no experience with OM606's, however I've owned a CNC machine shop for 31 years.
Personally, I would use thread repair system like Heli-coil (one of many brands). It is common practice in aerospace & tech industries to use a "theaded incert" in aluminum when heavier loads are being place on the threads... So actually other than the reduced sealing area on the face, this would be stronger than stock. As for the sealing area, increase the size of the counter bore and use a hardened shim washer.
Just my .02
GOOD LUCK!!!
RE: Snapped plug, damaged thread - fcp - 02-13-2013
The problem with the sealing area is the concave shape I think (its not a flat surface that you could use a shim in the way I think you intend) and its an area that I have hear others have problems with before -I don't know how it would be solved with a time-sert type insert..
This is the first multi-valve engine I've ever worked on (can you tell?
) so I speak with no authority of course just relying on the input form more experienced people.Research today and I found a replacement head from a documented sub 100K engine (same year and condition as mine) for around £250/ $400 complete with 60 day money back warranty. Given that it will be put on the flow bench and checked by someone who does know what they are doing (Ric Wood I think will do the work) I'm leaning strongly toward this option.
(I also lined someone up to perform the autopsy on the old head today - they have a big industrial band saw.. I think around 80 cuts will be needed - sounds like a few people would like to see this done)
RE: Snapped plug, damaged thread - Simpler=Better - 02-13-2013
A beveled plug could be manufactured, a machine shop is your friend for that.
$400 for a ported warrantied head is great...that's what I paid for a new heep head earlier this year
RE: Snapped plug, damaged thread - Joaquin Suave - 02-13-2013
Gosh $400 bucks... Go for it!
RE: Snapped plug, damaged thread - fcp - 02-13-2013
$400 is the warrantied head (complete with cams, sprockets etc), the porting and valve work costs more.. (a lot more actually) and is done by a specialist here -which is why I wanted to make sure I didn't compromise starting with a head that was less than ideal.
I will take pictures of the head before and after work and post here.
(02-13-2013, 03:12 PM)Simpler=Better A beveled plug could be manufactured, a machine shop is your friend for that.
$400 for a ported warrantied head is great...that's what I paid for a new heep head earlier this year
Someone else suggested that too.. The trouble is the cost of specialist engineering labor here is high..
The UK doesn't make anything anymore so general precision engineering companies that can do this work at reasonable cost are few in number and though we have great motorsport industry, those guys will be even more expensive to have them make something like this when it is so cheap just to buy another head.