Stripped Spark Plug holes

Post your general FAQs, comments & questions regarding all Ducati engine & transmission restoration here. [Specific engine FAQs should go in the 'BevelHeaven Garage' section.]
mizike77
860 GT / GTS
Posts: 272
Joined: Sun Jul 06, 2008 9:37 am

Post by mizike77 » Mon Mar 01, 2010 6:03 am

I had this problem on my Darmah. I swapped slides and all is well...... My pockets are NOT bottomless !
79 Darmah
78 900 GTS
86 F1B
80 SSD
02 Harley FXD
72 H2 750 triple
08 KTM 300XC
there has yet to be a motorcycle line made that is as satisfying to ride, hear and look at as the ducati bevels

DaveDare
Mariana
Posts: 29
Joined: Sun Jan 14, 2007 6:41 pm
Location: Brisbane, Australia
Contact:

Post by DaveDare » Mon Mar 01, 2010 11:05 pm

Bloody awesome guiys, interestingly I had this thought in bed last night and was my next question if anyone had found success doing this, so thanks for the answers. I will do a overhaul at some stage but I have spent so much getting this bike to a point of...still not running, I fear my luck is running on the thin side with my wife.

Also I am registering about 100 pounds compression in the front cylinder and about 126 pounds in the rear. I fear (somehow) my timing is out a few degrees. Any ideas on the simplest way to check and reset timing?

Thanks guys. Awesome info from this forum.

Dave::

ducadini
860 GT / GTS
Posts: 251
Joined: Sat Jul 31, 2004 9:54 am
Location: Antwerpen

Post by ducadini » Tue Mar 02, 2010 12:42 am

DaveDare,

Did Your machine-guy mate the head and cylinder after working on the head (I presume welding-drilling-tapping).

Could be the head is a little warped and looses compression.
Or one of the seats settled a bit more and needs to be mated to valve again.
Valves reshimmed ?
ALL Timing dots align ?
It is not so easy to get the timing a few degrees of (even more) unless You make major errors.
Compression check with slides open ?

If the wife gives me trouble spending time and cash on bikes, I get in the car and call her from a pub, wasted, and ask to come and get me.
Give her an option for YOUR time-spending :-D

cu
ducadini
Nego i ricordi peggiori
Richiamo i migliori pensieri

Lumpy
SD900 Darmah
Posts: 327
Joined: Sun Mar 25, 2007 5:49 am

cam timing

Post by Lumpy » Tue Mar 02, 2010 7:44 am

There is/was an excellent article on the DOCV web site titled The magic art of cam timing that goes into it in pretty good detail.

http://www.docv.org/cgi-bin/news/search.cgi
It`s all aimed at bevel twins and is in three parts. I checked mine on my GTS as it has desmo heads fitted but it was spot on. It is however not a quick 2 minute process and requires some tooling and patience. According to the article timing can be changed small amounts by moving a tooth on the bevel gears behind the alternator because it`s a hunting tooth system. I have also heard that Ducati bevels were renound for coming out with poor valve timing due to the maching tolerances and the accumlative error of going through som many gears. Read the article, it`s quite interesting anyway.
Generally speaking more often than not compression loss is due to poor seating valves or piston ring issues. A squirt of oil in the low pot will usually give an indication of poor ring sealing during comp testing. If the compresion comes up markedly it points to rings. In my opinion blow-by is the best indicator of rings not sealing. If shes blowing hard out the breather gases are passing the rings.
I had an issue once of a poor head to barrel sealing and found that it liked to let out a back fire at start up.
Another quick easy test for valve sealing is blowing compressed air into the plug hole with the piston at TDC compression stroke. It`s kinda fiddly cause you gotta seal the plug hole and use a regualor(most compressors have a reg fitted) and just push in a few PSI. Then drop your exhaust and listen to the valve. If they hiss she could do with a re-seat. The inlets can be heard by pulling the throttle up and listening down there. If they are really bad you can hear them hiss just by slowly rolling the engine over past TDC with the plugs in with the kicker and listen to them like that.
As with all fault finding, it`s worth going the hard yards to pin point the issue before you tear her to bits.

DaveDare
Mariana
Posts: 29
Joined: Sun Jan 14, 2007 6:41 pm
Location: Brisbane, Australia
Contact:

Post by DaveDare » Sun Mar 28, 2010 4:36 am

Hi there guys. Thanks Lumpy for the post. Have had a lot of drama after putting the head back on but think it might be rings now. Interestingly Lumpy I did do the oil squirt test just before you mentioned it on the post and the compression did come up to normal. i think maybe the rings are phuked.

Is there any way that a leaking head to cylinder could be covered up by this technique? I am reluctant to change the rings if it is still a leaking head. Or for that
matter if it is a poor valve seat, could the oil technique mask that?

Can I change the rings with the cylinder still in the bike and just pull the cylinder off?

Thanks guys.

Dave::

Lumpy
SD900 Darmah
Posts: 327
Joined: Sun Mar 25, 2007 5:49 am

rings

Post by Lumpy » Sun Mar 28, 2010 4:34 pm

It is possible to change rings with the engine in the frame. The back cylinder can be accessed by removing all engine mounting bolts except one (lower rear from memory)and tilting the engine down to access the rear pot. One point worth mentioning and you may already be aware but it would`nt be advisable to change rings in just one pot, you`d have to do both.
Checking the head to cylinder seal could maybe be done by spraying soapy water onto the joint and rolling her over and watching for bubbles. Another way is to get a friend to watch carefully with a torch in the right light conditions as she starts up. Some times smoke can be seen. Usually best done indoors and low light so the torch has max effect and no breeze around.
When using oil in the bore to check the rings it`s important not to put so much oil in there that it takes up cylinder volume and raises the compression like that.
While it is maybe possibly feasable that the oil could help a cylinder to head seal in a comp test I would imagine the leak would have to be pretty substantial if it`s showing up on a comp test at all and therefor would be fairly easy to detect.
Once again, f the rings are blowing by it will be huffing and puffing out the engine breather so I would checking there.
Another good method is to lure mechanicaly inclined friends over with beer and get their opinion. Nothing worse than ripping stuff apart to find the problem was`nt there at all and having to put it back together to find the original issue.

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