Lap, lap, lap your seats, under the diesel spring...

[Mark(The Miser)UK]

Yeah, it's a bit obtuse, isn't it.

We're talking about "lapping", one of the steps needed when rebuilding injectors:

http://vincewaldon.com/index.php?option=com_content&task=view&id=20&Itemid=28

Vince I have some questions re lapping:

1) Why do you have to lap the centre spacer? More-so why the top grooved side; especially as it will be mating back up with the injector top that it was mated to in the first place. Surely every face individually lapped runs the risk of tilting the plane of its mating face leading to uneven pressures, and at best distortion/leaks at worst?

2) Why are you taking off so much  flesh that it amounts to a decrease of 5 thou, or an increase of 15 bar on original spec  (probably more in reality, as it seems to me, with  the 20 [TD] injectors I've looked at, so far; most operate  at nearer 140 -145 bar). Thats more akin to grinding than lapping.

3) As I stated earlier in this thread why are people clamping down with such force in an attempt to  avert leaks? Aren't the grooves a sign of distorting everything as warned against in all good books  to avoid nozzle distortion; especially as the pintle can float on an oil film, and a good matched pair barely leak to the returns at all [when cold at least] I guess mating pressure is of the order of 60,000 psi.

'Newly into injector repairs'

[Duster 5.9]

Mark(The Miser)UK
I am going out on a limb to one suggestion and would work for me in that it would save me some money rather than buying all new injectors.

[Vincent Waldon]

Vince I have some questions re lapping:

1) Why do you have to lap the centre spacer? More-so why the top grooved side; especially as it will be mating back up with the injector top that it was mated to in the first place. Surely every face individually lapped runs the risk of tilting the plane of its mating face leading to uneven pressures, and at best distortion/leaks at worst?

2) Why are you taking off so much  flesh that it amounts to a decrease of 5 thou, or an increase of 15 bar on original spec  (probably more in reality, as it seems to me, with  the 20 [TD] injectors I've looked at, so far; most operate  at nearer 140 -145 bar). Thats more akin to grinding than lapping.

3) As I stated earlier in this thread why are people clamping down with such force in an attempt to  avert leaks? Aren't the grooves a sign of distorting everything as warned against in all good books  to avoid nozzle distortion; especially as the pintle can float on an oil film, and a good matched pair barely leak to the returns at all [when cold at least] I guess mating pressure is of the order of 60,000 psi.

'Newly into injector repairs'[/color]

Hi Mark... keeping in mind what my posted instructions say:

"This is how I do things… it is not necessarily the right way nor the best way !"

.... some thoughts:

1) In my mind when you rebuild an injector there are 3 "old" sealing surfaces (the top of the injector housing and both sides of the centre spacer) and one "new" sealing surface... the top of the new nozzle.  There are often visible grooves worn in at least two of the three... to me a quick pass on the third side is cheap insurance that *all* sealing surfaces are fresh.  I assume that the new nozzle has a fresh sealing surface... besides, I don't like to handle them anymore that I have to... insanely close tolerances within the nozzle !

2) Dunno what you mean here mate... nowhere do I specify 5 thou... or any other thou for that matter.  I gently lap with successively finer grit until I have a nice polished surface... and then adjust the breaking pressure to compensate as required.  If there are no grooves there is very little lapping required... if there are deep grooves then there's more lapping and more material removed.  I've never been scientific enough to record before and after popping pressure per injector so can't comment on how many bar mine specifically... more a general feeling that they go up some.. and as I say, it's gonna be dependent on how much grooving I'm faced with.

3) Can't comment on what "people" do... I specify the factory torque (70 Nm or 51 ft-lbs) and that's what I personally use.  I'd agree with you that overtorquing is a good way to distort the nozzle and risk pintle misalignment or binding.  

So far I've only had two leak that I can remember.. and in both cases I re-lapped rather than torquing harder... a bigger hammer is rarely the answer imho. ;-)

[Mark(The Miser)UK]

Vince I have some questions re lapping:


2) Why are you taking off so much  flesh that it amounts to a decrease of 5 thou, or an increase of 15 bar on original spec  (probably more in reality, as it seems to me, with  the 20 [TD] injectors I've looked at, so far; most operate  at nearer 140 -145 bar). Thats more akin to grinding than lapping.


'Newly into injector repairs'[/color]

Hi Mark... keeping in mind what my posted instructions say:

"This is how I do things… it is not necessarily the right way nor the best way !"

.... some thoughts:

2) Dunno what you mean here mate... nowhere do I specify 5 thou... or any other thou for that matter.  I gently lap with successively finer grit until I have a nice polished surface... and then adjust the breaking pressure to compensate as required.  If there are no grooves there is very little lapping required... if there are deep grooves then there's more lapping and more material removed.  I've never been scientific enough to record before and after popping pressure so can't comment on how many bar mine usually change by.. and as I say, it's gonna be dependent on how much grooving I'm faced with.


So far I've only had two leak that I can remember.. and in both cases I re-lapped rather than torquing harder... a bigger hammer is rarely the answer imho. ;-)

 Thanks for responding.

 My second point  was based on your mention of sometimes resulting in a 170bar  break pressure.... 170 -155 =15 bar. Each shim increment is 0.05 mm, for approximately 5bar pressure raise.  Thus .15mm  = .15/25.4 = 6thou. All my so far checked [gauge could be duff, thinking about it] TD injectors are between 135 and 145 bar

Do you think grooves are neccessarily  a cause of a leak, or  if the injector is not leaking not particularly a bad thing.
Hmm not sure if that's clear,,, Basically is it worth trying an injector  with a new nozzle without lapping even if it is grooved, if it wasn''t leaking before and  therefore the marks are possibly just cosmetic, seeing as lapping is somewhat time consuming?

[Vincent Waldon]

I'm beginning to feel that a quick pass with 1,000 grit to freshen the sealing surface might be the best initial approach.  Then, if any leak, address those specific ones with additional lapping.

Andrew

I'd concur... given that they are fine tolerance surfaces the less done the better.  I have a 4000 grit lapping bar that is perfect for touchups.

My only caveat might be that if I see visible grooves I'm likely to lap 'em rather than go to all the trouble of dialing them in first since I know that lapping away grooves is likely to invalidate the initial dial-in.

[Vincent Waldon]

Well there's my problem right there.... every diesel I own has had a cylinder stolen from it, since I only use *4* injectors.   :wink:

[duffer]

Could you give some details on the
   "4000 grit bar"?

   Is this the stuff used for polishing
   stainless steel?

   Do you just spread the stuff on a
   piece of plate glass, or what?

   I've been wondering about that
   stuff and any information you'd
   be willing to share would be much
   appreciated.

   Thanks, in advance.

[Vincent Waldon]

It's an actual lapping bar sold originally to hone woodworking tools.

Got mine from Lee Valley Tools:

http://www.leevalley.com/wood/page.aspx?c=1&p=33009&cat=1,43072,43071&ap=1


I lube it with diesel rather than water... works a treat and the price is pretty reasonable.

The only downside is that it's pretty soft... I find I need to true it fairly often.  Lee Valley also sells the tool to keep it true !

[Turbinepowered]

Hmmm, interestingly enough, the Dasher Bentley manual that I have (which gives "instructions" for rebuilding an injector, or at least taking it apart) makes no mention of lapping, grooves, or sealing surfaces.

I've dug out four more matching injectors, they're less "groovy" on the sealing surfaces, so I'm going to do the "just polish them up a tad" and test them out.

[edit] Forgot to mention I can't find the 3k water stone we have around the shop somewhere, it hasn't honed a wood tool in ages and is "expendable" in my father's words, so... 1700 grit sandpaper and light oil it is. I'll go extra easy on the finger pressure.

[duffer]

It's an actual lapping bar sold originally to hone woodworking tools.

Got mine from Lee Valley Tools:

http://www.leevalley.com/wood/page.aspx?c=1&p=33009&cat=1,43072,43071&ap=1


I lube it with diesel rather than water... works a treat and the price is pretty reasonable.

The only downside is that it's pretty soft... I find I need to true it fairly often.  Lee Valley also sells the tool to keep it true !

Thank you for that link.
I'll go down to Lee Valley and
check it out.

Thanks again

[Mark(The Miser)UK]

Hmmm, interestingly enough, the Dasher Bentley manual that I have (which gives "instructions" for rebuilding an injector, or at least taking it apart) makes no mention of lapping, grooves, or sealing surfaces.

I've dug out four more matching injectors, they're less "groovy" on the sealing surfaces, so I'm going to do the "just polish them up a tad" and test them out.

[edit] Forgot to mention I can't find the 3k water stone we have around the shop somewhere, it hasn't honed a wood tool in ages and is "expendable" in my father's words, so... 1700 grit sandpaper and light oil it is. I'll go extra easy on the finger pressure.

Turb.
I wouldn't bother with ultrafine grades.
If you make a mirror surface, and there is some mismatch, then higher torque pressures are needed to 'take up the slack' Using something like 600 grit, then the 'matt' surfaces  will bond better and the microscopic peaks and troughs will plateau, only as required.

 I would also leave water-stones behind. Use a Norton's type carborundum or  Al Oxide. Why? Well waterstones are excellent for sharpening blades knives etc; but at what point do you create an acceptable convex lap, before the stone needs periodic dressing.

The references to a lapping block in the Bosch manual refer to an impregnated steel block. A diamond one works well with a light pressure.


All disagreements welcome; after all, thrashing it out not only gets a result, it also tends towards the correct answer :twisted:

[Vincent Waldon]

The references to a lapping block in the Bosch manual refer to an impregnated steel block. A diamond one works well with a light pressure.

And to me, at the risk of thrashing this thread to death...  that's the point of all this. :wink:

There *is* an official way:  a precision diamond-impregnated steel lapping block.... I hear they're green in colour !  I also know that they are spendy little creatures.  I've read that there's a really really expensive microtome lapping machine for this task as well... takes off molecularly-fine layers of material in perfect alignment.

Given that I only do a couple of sets of injectors a year... I look for less spendy alternatives that approach the same results, particularly when safety is not compromised.  Fine sandpaper on glass, inexpensive water stones that need to be dressed now and then... stuff like that. It isn't the recommended method or the  recommended tools... but based on the scale of my operation I'm OK with the results. :wink:

I also substitute muffler clamps, impact wrenches, pieces of string, pieces of angle iron, fingernail polish, plastic putty knives, and various screwdrivers ground in all kinds of weird ways for the official tools... tools that I'd own if I ran a business but substitutions that make sense given the scale I operate at.

Actually, I do own the official exhaust clamp removal tool... it works well, but I sure wish I'd discovered this forum before I shelled out the hundred bucks !!!    :lol:

[blkboostedtruck]

score=
Vince= 6
miser=0

L.O.L. :wink:
Duane

[Vincent Waldon]

Nah.... no score.... we're all learning here.  

For starters, I'm keeping my eyes open for an carborundum or aluminum oxide stone because, yes, those water stones are pretty soft.

[Mark(The Miser)UK]

The references to a lapping block in the Bosch manual refer to an impregnated steel block. A diamond one works well with a light pressure.

And to me, at the risk of thrashing this thread to death...  that's the point of all this. :wink:

There *is* an official way:  a precision diamond-impregnated steel lapping block.... I hear they're green in colour !  I also know that they are spendy little creatures.  I've read that there's a really really expensive microtome lapping machine for this task as well... takes off molecularly-fine layers of material in perfect alignment.  

Owch...  I take your point. I don't even know where you'd get a lapping plate the size of the Bosch one.  I've seen a small one through a 'Google'. My old man has the waterstones. I happen to have collected the harder types, some are natural and some the Norton type. Frustrated by why the hell you rarely see them bigger than 6" x 2" or a 'giant'  8"  x 3"  I took to finding more than one of the same grit and imbedding them together into a block of wood.
I even made one out of a large piece of deglazed ceramic from the back plate of a toilet  cistern [er John :?:  :?: flush box?] Its about 8" x 1ft

Given that I only do a couple of sets of injectors a year... I look for less spendy alternatives that approach the same results, particularly when safety is not compromised.  Fine sandpaper on glass, inexpensive water stones that need to be dressed now and then... stuff like that. It isn't the recommended method or the  recommended tools... but based on the scale of my operation I'm OK with the results. :wink:

I totally agree on the less spendy routes. Every time I buy something for the car, I think well I only paid $60 for the whole thing! ... I regularly have to refocus :mrgreen: ...
New water stones or hard types  of any quality cost the earth over here, but we have something over here on weekends called 'carboot' sales [trunk :roll:]; where modern man gets rid of granddads rusty old [extremely high quality] tools to make room for shiney new stuff from Indochina :roll:   If I'm lucky one turns up for a $1 :lol:
Those cheap diamond impregnated plastic ones on Ebay for a few $ work well. I used an old 600 grit one on an injector last week to raise the b/p by 10 bar.
I also substitute muffler clamps, impact wrenches, pieces of string, pieces of angle iron, fingernail polish, plastic putty knives, and various screwdrivers ground in all kinds of weird ways for the official tools... tools that I'd own if I ran a business but substitutions that make sense given the scale I operate at.

Actually, I do own the official exhaust clamp removal tool... it works well, but I sure wish I'd discovered this forum before I shelled out the hundred bucks !!!    :lol:
12mm socket and extension on a 'Q'... But granny [turned 83 last week] does have that dreaded GTD, so I may have that to come :wink: