Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: McCabe-Thiele (Ted) on June 22, 2024, 10:15:41 AM
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I have a couple of stripped threads on two seperate carb bowls that I need to Helicoil.
After a lightbulb moment I realised I had an M4 repair kit that I bought a year or so ago & never used.
I've viewed a video on U tube so know about the tang that needs knocking out. It is also obvious that my Helicoil type inserts are too long. The Tap that came in the kit is a taper type so am conscious that it will soon contact the carb body as it is screwed in. The size is shown as M4*0.7.
Any tips from someone who has done this would be appreciated, can this be done with the carbs on the mounting bracket or do I need to remove them and hold the body in a vice taking measures to avoid the jaws marking the carbs?
Is it best to use a dremel blade to reduce the length of the Helicoil or are they available in the right length without buying a hundred?
I've tapped out threads before but never fitted my own Helicoils.
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You'd need a "plug" tap to have parallel thread into blind hole Ted, else the helicoil will also be forced into a taper as it screws is.
The helicoil winds in really easily, led by the tang, it contracts it's own spiral to make it really easy, but won't back out as that same spiral expands in reverse. Probably the easiest bit to do in reality.
Taper tap is to lead the tap into the hole by not trying to cut on its leading edge, and so gives more assured vertical to bore approach without much effort. Plug tap,to finish is engineering routine.
I'd wind the insert in then carefully cut off the excess with dremmel cutting disc if they are too long.
Tap carefully with plug, plenty lubrication and clean the bottom of the hole out as you go to get debris out of cutting zone.
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The tap that came with the kit is marked as STI4*0.7HSS the tip is pointed - is a plug flat at the end as well as no taper?
Any links to source a Plug Tap for the Helicoil as it's not a standard M4 tap?
Is this the type I need?
.https://www.ebay.co.uk/itm/156252954833
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Ted, long before dremels we had small triangular files and would file a V groove in thefitted coil just into the hole and break off the excess.
Let me look at my sets and if the M4 is a plug tap you can borrow it for post costs
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Kind offer Bryan might be worth me just buying a flat ended tap from a local engineering supplier - it will come in handy in the future no doubt.
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Its NOT a standard tap Ted, its a special that has the m4 profile and pitch on a bigger diameter to accomodate the coil widthx2
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Thanks I understand that Bryan.
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I have never found any firm selling just the taps except heliciol original and they were expensive
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I had this exact problem Ted, in the end I cut a thread it in af far as i cold before hitting the carb body then trimmed a coil to fit. Not ideal as there is very little thread length to bite on but it's working for now.
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In my engineering past when desperate, grinding a taper tap back (short) is one way of creating a bottom tap, if you have a spare.
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Hi Ted, I had one go and (for now) got away with a longer screw which reached some unused thread, and not over- tightened. Just a thought.
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Hi Ted, I had one go and (for now) got away with a longer screw which reached some unused thread, and not over- tightened. Just a thought.
I tried that by leaving the washer out - I'm going to do it properly - one day next week if I have a spare box of roundtoits.
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Got a squaretuit!
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My box is square - I suspect it's still empty!
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Ted, I replaced about half of the threads on my spare 400/4 carbs with helicoils. I use Loctite 648 when inserting then trim off any helicoil AFTER it has cured with the ol' dremel.
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I Helicoiled all my floatbowl threads 2 weeks ago, because three had gone bad loosening the bowls.
I ordered a set from Amazon, cost me 7 euro INCLUDING postage, took 3 days to get here and then spent less than an hour on a rainy sunday afternoon to put them in. The set was complete with all the tools I needed, drill, allen key, thread turner inner ;) and 24 coils, so enough spare to make mistakes (which I didn't).
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I have used a helicoil kit for 8-32 screws, repairing 7 of the 12 screw holes on my 77 550k. Also repaired a couple of holes on the S&S superleaker (Super E) on my harley. The kit had everything execpt the required drill bit to ready the hole for tapping. I believe it was an 11/64 inch drill required (apologies to metric folks). Only problem i had was breaking the tang in blind holes. Repairs seem to be holding.
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I have ended up cutting the tip off my existing Helicoil Tap with my Dremil type tool so it's now flat ended - it still has the tapered lead at the end so should be fine. I bought an M5 kit a while ago that came with plenty of coils.
I'm planning on doing a practice thread first on some scrap alloy that my brother has when I see him on Friday.
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Ted, I replaced about half of the threads on my spare 400/4 carbs with helicoils. I use Loctite 648 when inserting then trim off any helicoil AFTER it has cured with the ol' dremel.
Okay Matt, I have tapped out the two dodgy carb bowl threads so next I need to fit the coil inserts.
It was harder than I imagined to keep the Tap at 90 deg to the carb body - I now have some new threads.
I like the idea of giving the coil insert some extra intergrity using Loctite or similar.
With the Loctite 648 - is there any danger that the Loctite will seep through the coils and cause an issue?
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Ted, I don't think so. I would just let the Loctite cure.....
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I did wonder if J-B original cold weld (2 part) would work as an alternative as I have some left over from a previous repair job?
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That should be ok Ted, same as araldite i think, clean well with something like brake cleaner first and let it dry
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I ordered some of the Loctite 648 that was due for delivery yesterday Bryan but getting impatient so thought about the J-B as an alternative.
After more research I'm going to wait for the Loctite 648 - I've been away from the 500 for a month so another few days will not hurt.
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After my short summer recess I have finally fitted Helicoils to the two stripped carb bowl threads.
My first Helicoil was okay but I did not manage to get the thread as far down as I should have with the tap so the tang came off as I tried to wind it down the last bit. I have used a slightly shorter screw, Result!
Before I fitted the second Helicoil I ground off a tad more of my reamer with my Dremel. I managed an extra thread right to the end.
The Helicoil fits beautifully - so practice makes perfect proved yet again.
It's my first ever Helicoil so I am chuffed to bits & re-motivated to press on with the carb cleaning/re-fitting.
Just wondered if I ought to fit a new set of 40 jets or is there enough control with the air screws to cope with any enlargements caused by previous cleaning etc?
Comments welcome regarding jet replacement thoughts.