By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Forum House Ad Zone

McCulloch Strimmer problem

Magnets on hedge trimmer

All Topics | Latest Posts

Search for:  in Thread Title in  
David Clark 119/10/2011 15:17:47
avatar
3357 forum posts
112 photos
10 articles
Wanted for non internet user.
He has a McCulloch hedge trimmer and he does not get much spark.
The coils have been professionally tested and are ok.
He turns it over with a power drill and does not get a decent spark, sort of a flicker.
Anyone have any suggestions as what to test next. There is some slight magnetism in the magnets on the flywheel but he does not know how much magnetism is needed.
regards David
 
 
 

Edited By David Clark 1 on 19/10/2011 15:18:04

JohnF19/10/2011 15:57:23
avatar
1243 forum posts
202 photos
Presume he has tried a new or different plug?

Is it electronic ignition or a magneto? If its a magneto try a new condenser, at one time they either worked OK or were dead but now they don't die completely and can give the effect you are seeing.


Good luck John

Gordon W19/10/2011 16:02:41
2011 forum posts
Check the air gap between flywheel mag and coil end, if it's that sort. Don't know what the gap should be, but usually works at the minm. gap.
Richard Parsons19/10/2011 16:48:06
avatar
645 forum posts
33 photos

David


The McCulloch engines I have fixed have magnetos. They use a form of CDI units this takes the form of a pair of coils wound round a 3 poll pieces or sometimes 4 on older models. The magnets are generally fixed into the fly wheel in the form of a small patck of them.. There are no condensers or contact breakers in the classic sense.
Test 1 take a ¼” (not a 6mm) screwdriver place it on the magnet and try to lift the magnet. If you can lift the magnet –OK if you can almost lift the magnet Humph try it. If you cannot lift the magnet it is duff.

Ok you have had the poll pieces and coils tested.
If the magnet is OK then reassemble the magneto using a piece of normal paper folded in half as the distance piece between the magnet and the poll pieces. Do not connect the ‘stop wire' at this point. You should now try to get a spark. If you do get sparks at about 400 RPM, reconnect the stop wire and try again to get a spark.

That is about all.


Regards


Dick


Tel19/10/2011 21:03:35
avatar
157 forum posts
28 photos
The main problem is it's a McCulloch - best to throw it as far down the paddock as a double handed throw will allow and get a Stihl.
Stub Mandrel19/10/2011 22:03:17
avatar
4318 forum posts
291 photos
1 articles
In the old days they used to remagnetise magnetos by putting a decent DC current down the coils for a second or so (12V battery). If it still doesn't work, reverse the polarity (of the neutron flow?)
 
If it still doesn't work you have proably burned out the coil (don't blame me...)
 
Neil
Jeff Dayman20/10/2011 01:47:21
2356 forum posts
47 photos
"In the old days they used to remagnetise magnetos by putting a decent DC current down the coils"
 
Neil, I have no doubt that would have worked on some very old magnetos with soft iron bar or horseshoe magnets, but if you do that to any modern small engine magneto coil 1950's to now you will simply burn it out.
 
The McCulloch and most other small engine magnetos use powder metallurgy permanent magnets embedded in the cast flywheel to generate a primary current in the coil as the magnets pass by the coil's iron core laminations. The magnets do this by completing and breaking a magnetic field between the core and the magnets, inducing current in the primary coil. Older magnetos use points to trigger a high voltage spark in the secondary winding when the points open and break the primary current flow, with a condensor to limit current at time of the points opening to extend the point life.
 
Newer units have a second, smaller coil, called a trigger coil, which generates a signal voltage to switch an SCR and allow a large capacitor to discharge to the spark plug. The capacitor is charged by the primary voltage.This is CDI ignition. If the trimmer has CDI and there is no spark, there are no serviceable parts and the whole coil assembly is scrapped and replaced. They are usually potted with plastic inside a sealed case and when they go, they are gone.
 
Others have mentioned the flywheel to coil gap, and as suggested it would be worthwhile to try and set the gap with a few sheets of paper (about .006" is a common coil/flywheel gap spec).
 
Magnet strength is sometimes an issue with small engine flywheel magnets, my own rough test of the strength is that if it will hold up a 3/8" drive 1/2" socket stuck to the magnet when lifted up off the bench upside down, it is OK. However on very small engines like chainsaws and maybe this trimmer the magnets are much smaller and their attraction force is correspondingly less. If the flywheel in question will not hold up a 1/4" drive 1/4" hex socket it may have lost its magnetism, in which case a new flywheel is needed. They can not be re-magnetised, in my experience. I was told they are magnetized at the manufacturers' by holding them in an extremely powerful magnetic field generated by high currents in an induction coil.
 
If the gap check and magnet check result in no spark, and the trimmer is CDI ignition, then the coil/CDI assy needs changing out.
 
Good luck to OP with the trimmer. Are there any McCulloch dealers left in UK? None here in North America that I know of for parts anymore, but tyhere could be someone with a stash of NOS. You might check Smokstak.com's small engine forum.
 
JD
 
PS- TEL - the Stihl's are OK if you like boat anchors, but give me a Canadian made Pioneer saw or US made Remington saw from the 1960's - 1970's and I'll never get tired out - they're that much lighter, and have bigger engine power per CC than new ones of any make. Not many parts for them around anymore either though. 

Edited By Jeff Dayman on 20/10/2011 01:52:48

Tel20/10/2011 09:16:00
avatar
157 forum posts
28 photos
I love my Stihls Jeff, switched over from Husky's about 30 years ago and stayed with 'em ever since - we currently have seven working saws here and a couple of weedeaters.
Ian S C20/10/2011 11:31:21
avatar
7468 forum posts
230 photos
I'v got a McCullock chainsaw motor on the bench at the moment, I would like to know what sort of revs it does, its going to power a bike.
Before I overhauled it I looked up Mccullock overhaul on the net, and the method used is the rubbish wheelie bin, But it goes, so it stays.
I'v got access to a remagnetiser, and its been used on the mags for old hit and miss motors etc. Ian S C
KWIL20/10/2011 11:45:16
3681 forum posts
70 photos
My small McCulloch chainsaw uses a 30cc engine, about the same size as the strimmer. The magnet just tugs at a small 1/8" screwdriver when apprached from the back (ie through) the flywheel and it starts very easily on what appears to be a small spark. The settings of the needle jets are quite touchy, but once set are fine. It is a bit sensitive to over oiling the fuel.
 
I believe the old McCulloch company is dead and a new McCulloch seems to have appeared from the east.
wotsit21/10/2011 08:07:01
188 forum posts
1 photos
I had a similar problem with a strimmer, and got all this advice through this forum - in the end it turned out that the flywheel/magnet assembly had turned slightly on the crankshaft, so the timing was incorrect (I was assured this was absolutely impossible, since the wheel was keyed to the shaft - wrong - not sign of any key at all, simply a tight (?) friction fit). I can't account for the weak spark, mine was the same, but KWIL si probably right- there was only a very weak spark anyway - anyway, it ran fine once the timing was reset.
Stub Mandrel21/10/2011 19:19:30
avatar
4318 forum posts
291 photos
1 articles
Hi Jeff,
 
I accept my advice being out of date - I now that's how people 'restore' Fordson Tractor magnetos, although the owners manual advises buyiong new magnets (MRDA).
 
Neil
Ian S C22/10/2011 11:35:37
avatar
7468 forum posts
230 photos
With the older magnetos with iron magnets or ALNICO, it was important to not break the magnetic circiut, or the strength was soon lost, no problems like that with modern ceramic magnets.
My McCormick- Deering magneto servicing book even discribes a remagnetizer and its use. If your mag is the old points style check the condenser. Ian S C

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Sign up to our Newsletter

Sign up to our newsletter and get a free digital issue.

You can unsubscribe at anytime. View our privacy policy at www.mortons.co.uk/privacy

Latest Forum Posts
Support Our Partners
cowells
Sarik
MERIDIENNE EXHIBITIONS LTD
Shopping Partners
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest

 

Donate

donate