Keith W Posted July 8, 2015 Share Posted July 8, 2015 The bottom spark plug thread on no 3 cylinder on my 80hp rotax is just about stripped, I have been told that i cannot use a helicoil to repair it and I have to replace the head, can anybody tell me if that's true or any way to repair it, or as a last resort has any body got a head for sale, thanks Keith. Link to comment Share on other sites More sharing options...
Guest Maj Millard Posted July 8, 2015 Share Posted July 8, 2015 You can use a helicoil if the thread is still suitable for its use. You need to use the correct size helicoil and follow the instructions for its insertion. Lycomings and Continentals regularly use helicoil inserts. To avoid thread damage when inserting plugs alway thread in by hand initially to avoid cross threading. Link to comment Share on other sites More sharing options...
Keith W Posted July 8, 2015 Author Share Posted July 8, 2015 Thanks Maj the thread still looks alright but starting to pull a bit, just needed to know if it was a Rotax thing not to repair the threads but to replace the head thanks Keith. Link to comment Share on other sites More sharing options...
Guest Maj Millard Posted July 8, 2015 Share Posted July 8, 2015 You could also try running a thread chaser through ( correct size) this often cleans the thread out. Link to comment Share on other sites More sharing options...
Guest Maj Millard Posted July 8, 2015 Share Posted July 8, 2015 Good thread chasers are available from the Snapon man or other reputable tool stores. Link to comment Share on other sites More sharing options...
ozbear Posted July 8, 2015 Share Posted July 8, 2015 There is a repair called a keensert that will repair the thread and seat where a hellicoil won't do the job. 1 Link to comment Share on other sites More sharing options...
facthunter Posted July 9, 2015 Share Posted July 9, 2015 They are a bit bulky . The problem is seating the washer . You require the job to be perfectly true to the original axis and have a good area to seat. I would consider a tapered brass insert , tapped to the spark plug thread internally and faced flush after tightening well. Some alloy heads have such threads cast in from new. Nev Link to comment Share on other sites More sharing options...
cavalon48 Posted July 12, 2015 Share Posted July 12, 2015 like what others have said try a thread chaser, if using helicoil you need to pick up all the metal that falls into the bore, have done it in the past and used a flexible pen light and double sided tape on a long thin screw driver to pick the bits of metal. Link to comment Share on other sites More sharing options...
facthunter Posted July 12, 2015 Share Posted July 12, 2015 If you put grease on the tap and remove it a few times and wipe it. you will prevent most of the metal pieces going into the cylinder. Another way is to feed air into the other plug hole with both valves closed. This will blow the particles out as you cut the thread. Nev 1 1 Link to comment Share on other sites More sharing options...
Keith W Posted July 13, 2015 Author Share Posted July 13, 2015 Rotax will not repair spark plug threads with a helicoil or anything else, they reckon it alters the heat range of the plug and the heat retention of the head. 1 Link to comment Share on other sites More sharing options...
Downunder Posted July 29, 2015 Share Posted July 29, 2015 Rotax will not repair spark plug threads with a helicoil or anything else, they reckon it alters the heat range of the plug and the heat retention of the head. And they also get to sell a new head........ 1 Link to comment Share on other sites More sharing options...
geoffreywh Posted July 29, 2015 Share Posted July 29, 2015 Keenserts are very, very thin walled inserts and have a plug sealing ridge on the top (Top Hat shape) so there is no problem with plug sealing. just tap the hole (dont forget to chamfer the top of the hole slightly) and put them in with loctite hot retaining compound. I'm pretty sure I have all you need here. I'll have a look if you wish? Link to comment Share on other sites More sharing options...
facthunter Posted July 30, 2015 Share Posted July 30, 2015 The heat path through the thread will be altered a little (same as if the plug isn't tightened) You could run a colder plug. Another factor is the head cracking. Most cracks go from the exhaust insert to the spark plug, so an enlargement of the plug thread (which all thread inserts do) reduces strength a little bit. Cooler running liquid cooled heads should be less of a problem in this respect..Nev Link to comment Share on other sites More sharing options...
Keith W Posted July 30, 2015 Author Share Posted July 30, 2015 Actually Floods were very helpful and sold me a good 2nd hand head. 1 1 Link to comment Share on other sites More sharing options...
Downunder Posted July 30, 2015 Share Posted July 30, 2015 Actually Floods were very helpful and sold me a good 2nd hand head. Good to see they helped you out. I've got the impression Rotax ( not necessarily Floods) has pushed for profit increasingly over the past few years. Charging ridiculous prices for parts. Some people have picked up that the same parts are used on their other engines and are sold at a fraction of the price. You would think with the number of Rotax engines sold, the parts prices could be more reasonable. 1 Link to comment Share on other sites More sharing options...
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