Sand or Glass-Bead Blast-Cleaning is often Bad-News!
Posted: Sun Nov 22, 2009 3:55 am
____ Since the mid '70s I've been aware of a this trend which has really screwed-up way too many DUCATI motor-castings! ...
It seems that way too many people are so hastey to get their motor-parts cleaned-off, that they start their bead-blasting job before considering what could happen to all the internal threads of all the places where bolts & screws are meant to screw into!
So what then happens is all those screw-holes get that darn blasting-dust into them! _ And it's no easy task to get it all out!! (Air-blasting doesn't get it all out!)
And so when ya then try to insert the screw, you feel the grit just grinding away at the weak alloy threads, (if you can even get the screw all the way in)! _ Very bad news!
__ So to anyone who intends to do any kind of blast-cleaning, please don't overlook doing something to protect all those theaded holes, from any dust!
Even after I have warned people about this issue, I've still learned of instances where they were still too hastey to get the job done, and went & forgot to insert the screws into the holes, as I had suggested! _ So DON'T FORGET!
Just first put a bit of grease into the holes, and perhaps also smear some on the threads of their screws, and put the screws all the way into their holes, BEFORE starting the blast-job!
You'll then not only save the threads, you'll also spare yourself of any related troubles!!
____ Now for those of you who have already done the dirty-deed, here's what ya need to do in order to undo the potential for bad thread-damage.....
You'll need a 6x1.0mm tap with a flattened (unpointed) tip (often referred-to as a "blind-hole tap"). _ After ya place some grease between it's rows of cutting-threads, insert the tap into the hole and thread-in only about 5 to 10 turns inward, then, unscrew outward & remove. _ Then inspect the tap and wipe-off any contaminated grease. _ With any such grease replaced with fresh, repeat the thread cleaning job, going into the hole just another 5 to 10 threads further inward.
Remove & repeat the process until the tap has bottomed-out at least once.
__ In the more contaminated cases, you may encounter sufficiant resistance before as many as 5 turns inward... In such cases, you may need to do the suggested process as many as 10 to 20 times (per hole *), in order to get ALL dirt removed from & out of the threaded-hole (* and so as to better help prevent any probable dirt build-up within the tap-flutes from possibly getting jammed-against the threads).
__ Because you're using a flat-nose tap, in this process you will then also be creating new threads (all the way to the bottom, of each hole). _ So when the job is done, you can & should then use longer screws than stock.
I've found that for the sidecover-holes on either side of the crankcase, all screws can then be increased in length, (by either 5 or 10mm) !
And for the cyl.head, most of the rethreaded holes can then make use of 25mm screws, (in place of the stock 15 or 16mm screws)!
However the four upper screws for the valve-covers, (which are located above the rockerarm-pins), can not be longer than 18mm.
__ Concerning the cyl.head, even if it has not been exposed to any kind of blast-cleaning,, for anyone who happens to have a head which came with the extra-short 15mm screws, I highly recommend that you replace them all with 18mm (1.0mm thread) screws!
(I'll post another tech-tip on that subject as soon as somebody asks for any additional details on it.)
___ I really hope that this posting will stop at least one more occurrence of this fairly common mistake!
Your True DUKE-Tech,
DewCatTea-Bob
It seems that way too many people are so hastey to get their motor-parts cleaned-off, that they start their bead-blasting job before considering what could happen to all the internal threads of all the places where bolts & screws are meant to screw into!
So what then happens is all those screw-holes get that darn blasting-dust into them! _ And it's no easy task to get it all out!! (Air-blasting doesn't get it all out!)
And so when ya then try to insert the screw, you feel the grit just grinding away at the weak alloy threads, (if you can even get the screw all the way in)! _ Very bad news!
__ So to anyone who intends to do any kind of blast-cleaning, please don't overlook doing something to protect all those theaded holes, from any dust!
Even after I have warned people about this issue, I've still learned of instances where they were still too hastey to get the job done, and went & forgot to insert the screws into the holes, as I had suggested! _ So DON'T FORGET!
Just first put a bit of grease into the holes, and perhaps also smear some on the threads of their screws, and put the screws all the way into their holes, BEFORE starting the blast-job!
You'll then not only save the threads, you'll also spare yourself of any related troubles!!
____ Now for those of you who have already done the dirty-deed, here's what ya need to do in order to undo the potential for bad thread-damage.....
You'll need a 6x1.0mm tap with a flattened (unpointed) tip (often referred-to as a "blind-hole tap"). _ After ya place some grease between it's rows of cutting-threads, insert the tap into the hole and thread-in only about 5 to 10 turns inward, then, unscrew outward & remove. _ Then inspect the tap and wipe-off any contaminated grease. _ With any such grease replaced with fresh, repeat the thread cleaning job, going into the hole just another 5 to 10 threads further inward.
Remove & repeat the process until the tap has bottomed-out at least once.
__ In the more contaminated cases, you may encounter sufficiant resistance before as many as 5 turns inward... In such cases, you may need to do the suggested process as many as 10 to 20 times (per hole *), in order to get ALL dirt removed from & out of the threaded-hole (* and so as to better help prevent any probable dirt build-up within the tap-flutes from possibly getting jammed-against the threads).
__ Because you're using a flat-nose tap, in this process you will then also be creating new threads (all the way to the bottom, of each hole). _ So when the job is done, you can & should then use longer screws than stock.
I've found that for the sidecover-holes on either side of the crankcase, all screws can then be increased in length, (by either 5 or 10mm) !
And for the cyl.head, most of the rethreaded holes can then make use of 25mm screws, (in place of the stock 15 or 16mm screws)!
However the four upper screws for the valve-covers, (which are located above the rockerarm-pins), can not be longer than 18mm.
__ Concerning the cyl.head, even if it has not been exposed to any kind of blast-cleaning,, for anyone who happens to have a head which came with the extra-short 15mm screws, I highly recommend that you replace them all with 18mm (1.0mm thread) screws!
(I'll post another tech-tip on that subject as soon as somebody asks for any additional details on it.)
___ I really hope that this posting will stop at least one more occurrence of this fairly common mistake!
Your True DUKE-Tech,
DewCatTea-Bob