7 replies to this topic

[bitten192]

Where can I get an inexpensive 12mm spark plug thread chase? I do not want to cut new threads. I just want to clean the existing threads. Most 12mm tools I've seen are repair tools.

[sandpiper]

My recollection, and Roger can set me straight if I am wrong, is that Rotax does not recommend use of the thread chase. But, if you go that route, just remember that a year ago each head was $1700. Probably more now so extreme care would be good.

[bitten192]

sandpiper, on 31 October 2011 - 12:46 AM, said:

My recollection, and Roger can set me straight if I am wrong, is that Rotax does not recommend use of the thread chase. But, if you go that route, just remember that a year ago each head was $1700. Probably more now so extreme care would be good.

Maintenance Manual says you are supposed to clean threads. How do you do it?

Ernie

[Roger Lee]

If you totally damage your plug threads so done except for the expensive replacement head. That said if you just have a bad couple of threads it can be fixed. You don't want to CUT new threads only reshape the ones you have.   Either toll listed below will get the job done and not leave filings in the cylinder because you are only dressing up the old threads not cutting new ones. If plugs don't screw in easily then stop and start over or fix the one crossed thread right then and there.


http://www.nextag.co...871/prices-html


http://www.amazon.co...ASIN=B001SOHXLQ

[sandpiper]

Ernie - I know the manual says that and I don't have a good answer for you. Maybe Q-tips? I had the same question at Rotax school and discussed the thread chaser with the instructor, Eric Tucker. He recommended, as I recall, that I not use a thread chaser on good threads. Do you have a problem with your threads being dirty, or are you just wanting to follow what the manual says to do as a part of your routine maintenance?  If you are not having a problem and you are not having trouble getting plugs in/out then I would just leave them alone.

[Roger Lee]

Use this as it works from the inside out and with a touch of grease on the threads of the tool you won't have any issues. The other tool I listed above works well. You aren't cutting new threads so you shouldn't have filings. You are only reshaping them with that small thread chaser.

[bitten192]

Roger Lee, on 31 October 2011 - 02:20 PM, said:

Use this as it works from the inside out and with a touch of grease on the threads of the tool you won't have any issues. The other tool I listed above works well. You aren't cutting new threads so you shouldn't have filings. You are only reshaping them with that small thread chaser.

Threads are fine. I had trouble getting compression tester hose into #3 spark plug hole because of hose interference and crud on the threads. I finally used a 12mm thread repair nut on an old spark plug to clean up it's threads and used the plug to clean up the top of the hole. Put a little heat conduction paste on the hose threads and it went right in.

I used a wooden dowl rod covered with a shop rag to clean up the spark plug holes. Plugs went in easily.

thanks

Ernie

[Jeremy MacGregor]

The Spark plug thread chasers are fine, we use them all the time in the overhaul shop. Just use good judgment, obviously make sure your going in straight (1700$ just for the body of the head) If done properly there should be little to no metal debris on the chaser when your done, just silicon paste and some carbon. It is a really good idea to do it with the head off. The cylinder clearance is about 0.001" and we have relatively small valves so if there's any chance of aluminum debris getting in there then do yourself a favor and pull the head because it won't be exhausted easily.