Cleaning cylinder bolt holes? - Page 2 - PeachParts Mercedes-Benz Forum

Wayfarer · #16 04-21-2010, 05:42 PM

Well, I went home over lunch and measured the threads on one of the old head bolts. It's M10 x 1.5 not 1.25. So now I have an incorrect tap on it's way to me next week.

(Edit: I just called the store here in Boise and they are sending me the correct size tap...it wasn't too late to change the order.)

OK nate, so you're saying that I shouldn't use a tap at all unless it's a "repair" tap? I had a heck of a time finding a tap at all, and nothing I saw online or elsewhere mentioned "repair" anything. Are the ones junkman linked to at doitbest.com "repair" taps? If not, do you know where I can get one? I'm in Boise, so I have most retail stores available here in town. Thanks.

leathermang · #17 04-21-2010, 07:49 PM

A Bottoming tap should only be used after a regular or chaser ( I do not believe it makes any difference on this deal ) tap has been used to get as far as it will reach... just for the final few threads cleaning.
You do not need to determine oil vs dry thread friction..
The torque values given in the FSM assume ' lightly oiled' threads and bolt....

Crazy_Nate · #18 04-21-2010, 08:59 PM

Here's a brief article about tapping versus cleaning: http://www.carcraft.com/techarticles/thread_chasing/index.html

leathermang · #19 04-21-2010, 09:42 PM

Quote:

Originally Posted by Crazy_Nate

Here's a brief article about tapping versus cleaning: http://www.carcraft.com/techarticles/thread_chasing/index.html

Those people are SELLING things...

This part " Standard taps are actually designed to cut new threads rather than chase existing ones. Every time you use a standard tap to chase a set of head bolt threads, for example, the tap will also remove more of the existing threads." from that page is NOT TRUE....

The first sentence is true... but does not apply to this situation...
The second sentence is NOT TRUE.... what is removes is trash, rust and anything else that should not be there...

You can check this be drilling and tapping a new hole... then running that same tap in and out.... you will NOT be cutting any more stuff out of those threads after the second run through... it just goes in and out just like it was a bolt....

This is assuming that your tap is of the same ' percentage ' cut as the original... IF you use a different one for your cleaning then it will cut the first run.. BUT you would have to order that special... if you get a standard tap you will not have any problem with cutting out metal that should be there.

Crazy_Nate · #20 04-21-2010, 09:51 PM

I don't really feel like getting into an argument, but this deals with tolerances. Tolerances on the nominal diameters of threads and the proper depths. You take off too much material and you'll change the required torque for the proper fastener preload.

Retapping a thread will enlarge it... There's a reason why you use a go-no-go gauge to test threads and not a tap.

PS: the article was meant as a brief reference. I don't have any sort of vested interest in selling any products

mplafleur · #21 04-21-2010, 10:18 PM

Quote:

Originally Posted by leathermang

The torque values given in the FSM assume ' lightly oiled' threads and bolt....

Don't forget to oil the shoulders as well.

leathermang · #22 04-21-2010, 10:22 PM

Nate, a good discussion of the facts is not an argument ..... and I did not think you had an interest in them selling stuff... just that they said things for that purpose and you did not catch the difference between reality and what they were representing....

" Retapping" UNLESS you use a tap with a different amount of thread overlap than standard....will NOT TAKE OUT ANY MORE METAL..... read my post number 19 carefully...

Crazy_Nate · #23 04-21-2010, 10:43 PM

Yeah, I think we're converging on the same point. If you're removing a lot of material, the same tap will remove a different amount than if it was less material (say, 70% nominal diameter of the fastener versus 75%).

I would say it would matter less with more rigid materials. I see a lot of aluminum sheet metal... it definitely can be over-done by somebody not paying attention. Steel? Probably less likely. If you can clean the threads with the cutting tap and have very little resistance, it might be fine. I just tend to err on the side of caution. It's very easy to remove material, but much harder to get it back. The "cleaner" taps are usually of different geometry to prevent them from enlarging existing threads.

Going back to tolerance, I'm not sure of the specification from the factory manufacturing procedure, and I'm not sure of the design specification. All I know is that those Mercedes engineers were (are?) quite good

t walgamuth · #24 04-21-2010, 11:04 PM

Quote:

Originally Posted by LarryBible

Failing the availabilty of a bottoming tap, not a tapered tap, chuck an old head bolt or a bolt of the correct size in a vise and us a three corner file to put some cutting edges perpindicular to the threads.

A bottoming tap works great AS LONG AS you don't apply any force to it. You should be able to start it with only finger force and then run it with no resistance. If you have to pull on the wrench it is starting new threads as opposed to chasing the old.

Hey Larry! Good to see a post by you. I have noticed your name on a few old threads recently and was wondering how you are. I hope you are well.

Welcome back!

Diesel911 · #25 04-22-2010, 01:26 AM

Quote:

Originally Posted by Wayfarer

Now I'm not sure of the head bolt size I have. Are they M10 x 1.25 or maybe M10 x 1.5? I thought they were 1.25 but now I'm not so sure. Engine is OM602 5 cyl. Can someone confirm?

Random thoughts:
In the case of this Thread using a regular Tap is not going to cause any problems with weaking the threaded area in the Block.

In a regular shop the Boss might supply a set of taps or you might have to supply your own.
If the Shop supplies a Tap Set you can bet they will be abused, dull.chipped and some will be missing. If they can find the right size some people in the shop are going to use those Taps anyway.

So you buy your own in the commonest sizes just to make your job easier.

I have never worked any where that used special Thread Chasing Taps. Either you used your own Taps or what ever your shop had to do your chaseing and Threading.

It makes sense for Racers to use special chaseing taps as they take the Engine apart a lot and losing a Race due to Blown Head Gasket or other issue can be very expensive.

I do not understand how running the same Tap through the same hole will cut more each time it goes through? I could see that happening if you used a different Tap each time you chased the threads due to slight differances in dimensions.

When a Bolt goes down into a hole there had to be some clearance for stuff like Oil to be squeezed passed the Threads or you would end up with a Hydraulic lock.
This is where that percentage of contact of the Threads comes into play and it also depends on the material that is being threaded.

One way to find the correct size is to take a Bolt to a Hardware store that has Metric Nuts. In this caw they would most likely have the M10x1.5 nuts. If your Bolt does not fit that I would ask the Sales Person to check it with a Thread Gauge.
1.25 is a finer thread than 1.5

leathermang · #26 04-22-2010, 09:03 AM

Diesel911, Thanks for posting those random TRUE thoughts !

SD Blue · #27 04-22-2010, 11:09 AM

A quality tap source:

http://www.fastenal.com/web/locations.ex?action=search&searchType=locations&zip=Boise&state=ID

http://www.fastenal.com/web/products.ex?N=0&Ntk=Search+All&Ntt=10-1.5+tap&Ntx=mode+matchallpartial&Nty=1&D=10-1.5+tap&Dx=mode+matchallpartial

Crazy_Nate · #28 04-22-2010, 05:01 PM

So, I just happened to have a quick chat with our CNC machinist about tapping.

Obviously, not all taps are created equal. There are H-ratings (pitch diameter limits), H2, H3, H4, H5, etc. They matter sufficiently for flexible material or for any sort of coating (necessary to maintain tolerance). Our shop works primarily with aluminum (5052 H32 or 6061 T6), as well as several plastics like delrin. For aluminum, the taps are sized based on which alloy and the finish (such as anodizing). The cleaner taps are undersized to prevent removal of additional material.

For steel, being much more rigid of a material, it matters less, as the material does not deflect as much under the load from the tooling. I think my worry is a little misplaced here, as, we're ultimately talking about one or two thousandths of an inch. Some applications it may matter. If I was just cleaning the threads in the cylinder head, I'd still get the proper 'cleaning' (undersize) tap. It's not like I have to tap a lot of metric threads anyways

Now, to further confuse the subject...most of the threads I work with are UNC / UNF. Metric may have different standards that might not even be applicable to what I've said.

Standard tap markings: http://www.natool.com/files/documents/Tap_Marking.pdf

Cheers!

Chas H · #29 04-22-2010, 05:06 PM

I've made chasers out of bolts and they work fine- grind 3 grooves down the length of the threads. Run a head bolt you plan to use down all the cleaned holes as a check for clean before fitting the gasket and head

#30 04-23-2010, 11:17 AM

You don't have to get crazy about this! This is a RIGID tapped hole. You are only getting the dirt out. If a tap gets at all difficult to turn, pull it out, put a little solvent in the hole and blow it out with compressed air before trying again. After you CLEAN the threads with the tap, ALWAYS blow out the hole with compressed air.

If the tap becomes too difficult to turn THEN you might be enlarging the threads and you need to determine what's going on.

We're indeed working on precision manufactured automobiles, but they're NOT 747's.