Cleaning cylinder bolt holes?

[Wayfarer]

I am about to put my freshly rebuilt head (thank you metric motors) back on my 1992 300D 2.5. I think I have everything ready to go, except for cleaning the cylinder bolt holes. I went to every store I could find for a tap in the correct size (10mmx1.25, I believe) and could only find one special order from NAPA at $30. So I about to give up on the tap idea. Do I really need to run a tap down those holes or can I just use liberal amounts of compressed air and brake cleaner, a brass bore brush, shop vac, and q-tips?

I know if I don;t get them clean, they won't torque or seat properly, especially of there's any liquid in the hole. Do I need to get the holes perfectly clean or is a "90% solution" ok? Any other suggestions or pitfalls I shuld be aware of?

Thanks.

[vstech]

you must chase the holes, and clean out the debris. and the bolts must be lubed with engine oil when you install them. otherwise the torque and subsequent angle settings are useless. do you wanna change the head again?

[Wayfarer]

Where do I get the appropriate tool? Is a tap in the correct size ok or will I damage the threads, because I'm a little worried a tap may be too hard of metal?

[Junkman]

http://doitbest.com/search-10mm+tap.dib

Buy as needed or you can buy a cheap set from some place like harbor freight and replace as needed.

Local hardware store here has a decent stock of individual metric tap & dies.

[vstech]

actually, you don't wanna use a tap. you want a thread chaser. a tap is capable of damaging the threads, especially if you use a cheap tap!
a tap is tapered at the front, and usually has a sharp point, you want to use a flat tipped chaser, that has the correct size thread all the way to the point.

[Wayfarer]

vs, that's what I was worried about. I was thinking that since the tap is hard carbon steel it could potentially damage the threads.

So can you suggest where I could by a proper thread chaser? I was thinking about taking one of the old head bolts to a machine shop and havng them cut some lengthwise grooves in it and using that to chase the threads. Would that work or should I try to find an actual thread chaser?

junk, thanks for the link to the tap. If that's what I end up using, getting for $5 instead of $30 is the preferred route.

I just went ahead and ordered that tap, 10mm x 1.25, just in case. $5, be here next Wednesday though.

[mplafleur]

On the cheap side, you could use an old head bolt.

[Wayfarer]

Originally Posted by mplafleur

On the cheap side, you could use an old head bolt.

If I do that, how should I tel the machine shop to cut the bolt? You do need a groove for the debris to be caught into, I would think, unless your talking about just pushing it all to the bttom and then getting it out with a q-tip or something.

[Diesel911]

Originally Posted by Wayfarer

vs, that's what I was worried about. I was thinking that since the tap is hard carbon steel it could potentially damage the threads.

So can you suggest where I could by a proper thread chaser? I was thinking about taking one of the old head bolts to a machine shop and havng them cut some lengthwise grooves in it and using that to chase the threads. Would that work or should I try to find an actual thread chaser?

junk, thanks for the link to the tap. If that's what I end up using, getting for $5 instead of $30 is the preferred route.

I just went ahead and ordered that tap, 10mm x 1.25, just in case. $5, be here next Wednesday though.

I would not use the Harbor Freight Taps on the Cylinder Head as I have a Harbor Freight Tap and Die set and I have some Made in Japan Taps and Dies. The Quality of the Harbor Freight ones is too poor.

The Tap is supposed to be hardened and if the Tap is the correct size it will not Damage the threads.

[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?

[leathermang]

DO NOT use an old head bolt....

as to taps being sharp on the end.... only one typical type is...

The problem is also that some taps are for different ' percentage ' contact between the bolt and the threads...

"The Tap is supposed to be hardened and if the Tap is the correct size it will not Damage the threads. " Diesel911

True....

but I think some people are not good about being careful with the sharpened end taps in terms of getting them lined up correctly....and not forcing them when getting lined up with the center line and where the threads needing cleaned up are...

If you want to go sorta ' insider machinist' ... you can get a spiral tap of the correct size...it may be listed as a gun tap or something.... easier to line up...

Also, taps are typically of three types with regards to the depth they will cleanly cut the threads... and the one which will go the farthest into the hole are called ' bottoming ' taps... which is pretty blunt on the end... but NOT the first one you would use ... it would be the last of either two or three tap types ( if you want to be an ' inside machinist' ) ...LOL ... so it would be the sharpened type first.. then the bottoming tap...
Depending on the relationship the factory put into the bolt length compared to the depth of the hole.. ( or the compression of the head gasket , etc) then the bottoming tap might be VERY important.... few do this though.... I am just ( probably ) giving you something to think about....

Mainly... no matter which you use.... is to be patient... do not rush anything... use your fingers to run it in as far as it will go... if your holes are really in good shape you can do the whole thing with your fingers... ... keeping in mind that means having heavy grease in the chip reliefs... be sure to use a regular tap holder otherwise so you can feel ' straight' and when you face resistance...
TAKE it back out and clean it very often...maybe every couple or three turns if you feel it is cutting as it goes in.... take all the grease out... resupply the grease...and go in again... patience means everything in this job... yes, it is boring ( no pun ) .. but cleanliness is everything on this job.

[toomany MBZ]

Originally Posted by vstech

you must chase the holes, and clean out the debris. and the bolts must be lubed with engine oil when you install them. otherwise the torque and subsequent angle settings are useless. do you wanna change the head again?

You need to determine if the torque values given are for oiled and what kind, vs. dry.
http://www.imperialinc.com/pdf/A_FastenerTorqueCharts.pdf
http://www.mobilecal.net/pdf/TORQUE_B7Studs.pdf

[Wayfarer]

Wow, thanks for all the replies and great advice.

I think the best route then is to go with a tap and go SLOW, fingers only, grease in the groove, new grease every 3-4 turns depending on how dirty.

Harbor Freight in Boise, btw, did not have ANY metric taps when I stopped by this week and last week, so I gave up on them. Probably just as well if the quality is not up to snuff.

Now if I can just find out for sure whether the tap I just ordered via the link above is the right size. M10 x 1.25. Is this the correct thread size for the OM602 head bolts?

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.

[Crazy_Nate]

My advice is only use the PROPER repair tap (sometimes called a chaser, etc). Running a tap through a second time will enlarge the threads...not clean them.

Again, do NOT use the standard tap... Make sure to use proper lubrication