Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: Johnny4428 on December 05, 2020, 09:59:31 PM
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Here’s a serious dilemma! Is it worth refurbishing old coils? By the time I have sourced new ht cable, protective sheaths, numbers, epoxy resin etc, I am still going to end up with 47 year old coils. So the question is any advantage in repairing compared to replacing with new.
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.... it surely depends upon how anal you are about original parts? Whilst I personally enjoy a good challenge, modern stuff is generally very reliable, beautifully made... and at reasonable cost that it’s sometimes sensible to know when you’re beat!
Coils - I’d shy away from given 40yo insulations becoming brittle, the environment they sit in, and that pushing any bike home is no fun!
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you could try checking (with a multimeter) the reading(s) to see how good/bad they are before anything else.
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I've got repo's on my 750k2 and had no problems (only 500 miles though) but had 2 out of 2 coils (M&P repo's) go duff on a K6 I built recently. If you follw Ash's guide, he considers that the standard coils are bullet proof and shows you how to test them before paying out for all the stuff to refurb the std ones. The cost reduces the more you do - I've done 3 sets now and so the cost compare to std replacements (few hundred squid?). I have a set ready to put on the 750k2 and a set for my 500k2 I'm building. The other set went on a recently sold K6 cafe racer.
I quite enjoyed the challenge and achievement of bringing what was effectively a throw away part back to new! (all thanks to Ash's guide mind you!).
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+1
I did the same. The only thing was the knowledge of where exactly to cut the body and the confidence to do it.
Also, do pay attention to teh advice not to cut too close to where the lead joins the coil; it is a pain to try to solder it back here.
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Truthfully, little is allowed to die in our house, which Mrs Lobo will glumly attest to.
Yesterday however, I began to refurb a worn out 1.5HP water pump (we’re on rain tanks here), which was really unnecessary as I’d bought a new replacement at very reasonable cost & slotted it in (within 15 mins) a couple of days ago.
Anyways, after 2 hrs of sweat (33 degs at the mo), wet with penetrating oil, sheared studs, plastic parts frozen into rust, ball races stuck onto corroded shaft.... and worst, the prospect of cleaning, etch priming and painting the old casing .. I gave up. Perfectly doable, but when labour / balls-ache etc factored in against replacement cost it really was a no-brainier.
A strangely lovely feeling to dump 13kg of old pump into the bin! I showered, saw your post Johnny and had to reply.
On reflection, it really would depend (for me) upon the rarity & originality of the machine in question.
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Don't want to get into a debate about it ..you make your own decision.
All I can say it I have done a few sets for Trigger, RGP750, Julie etc on here and they are people who have pretty exacting standards and their standards of restoration I truly admire..
Also investing in the clear epoxy resin kit I recommend will pay dividends as it's one of the best adhesives on the market for all other stuff. Forget Araldite, Gorilla Glue uncle Tom Cobley and all b*llocks glues..I have been using it for over 30 years and you can't beat it. Plus it can be filled with ultra fine aluminium powder or ceramic powder to create a really strong repair putty (if you look at a CB750 early engine there are apertures blanked off at the the factory using a similar aluminium filled epoxy resin..and I have never seen it fail.. as long as the preparation is good.
I have a set of coils to do for Julie's 400/4 'Hettie'... When I do them I will try and do a video for anyone who is interested.
If I wasn't repairing them I would buy the OEM Denso ones that Yamiya sell. If the primaries of any other aftermarket ones are less than 4.5 Ohms I would dismiss them out of hand if you are using the standard points system.
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Yes I'm interested as one of my coils definitely looks in need.
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The way Ash does them is spot on.
I have had a go myself some years ago but, i couldn't get the soldering right and it would not take. Not sure if it was my solder, flux or soldering iron was not powerful enough. I must admit that i am shite at anything electrical so, i leave stuff like that to the experts ;)
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I have a set of coils to do for Julie's 400/4 'Hettie'... When I do them I will try and do a video for anyone who is interested.
I for one will be interested to see it.
I have a couple of sets that could do with doing when i pull my finger out. ;)
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Great advice and comments, all welcome. I think I will probably have a go at repairing if the test on the coils with multimeter proves to be ok. I will of course be interested in viewing any repair videos on this subject too.
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Ash, just out of interest, what is the failure pattern of old coils? Is it an ‘easily’ addressed mechanical failure, or a breakdown / degradation of component parts?
Simon
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The way Ash does them is spot on.
I have had a go myself some years ago but, i couldn't get the soldering right and it would not take. Not sure if it was my solder, flux or soldering iron was not powerful enough. I must admit that i am shite at anything electrical so, i leave stuff like that to the experts ;)
Graham,
A lot of the old wires oxidize and go black in color.
The best thing to do in that case is use some good old fashioned plumbing solder and leave it to do its stuff for half an hour before using resin cored solder. ;)
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Ash, just out of interest, what is the failure pattern of old coils? Is it an ‘easily’ addressed mechanical failure, or a breakdown / degradation of component parts?
Simon
Of all the coild I have fixed, only one was not repairable as the secondary HT winding was low resistance. The main failure is fatigue of the conductor core of the HT leads. I think the failed one had been fitted with a CDi aftermarket ignition. In this instance, if there is no spark plug present or or some kind of break in the HT cable conductor core then the excessive HT created in the secondary can cause 'flashover' and damage the windings.
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Bit of an asside but when laverda put bosch electronic on the 3 cyl just taking a plug out and resting it on the head destroyed the system