One step forward, then a brief clatter and the engine stopped

250 2c- the Wee-WeeVees
julianharty
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Location: High Wycombe Area (Bucks)

Re: One step forward, then a brief clatter and the engine stopped

Post by julianharty »

mbmm350s wrote: 10 Jul 2024 11:15 I wonder how bad the plug thread is could it be recut? If not a proffesional thread insert would be needed
I have a wonderful reverse thread cleanup tool which I used after removing the remnants of a broken spark plug (the top had been sheered off before I bought the bike leaving the rest of the spark plug seized in the head) in the front cylinder head. The tool is the: Sealey Ms003 Reverse Action Spark Plug Thread Chaser, BTW. I used this to clean up both head's threads (and on my kanguro heads, etc.).

The damage to the thread this time is extensive so I'm convinced that either a helicoil or an insert are necessary. I might do some more measurements for the record :)
julianharty
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Re: One step forward, then a brief clatter and the engine stopped

Post by julianharty »

mbmm350s wrote: 10 Jul 2024 10:19 Of course that washer could have been in the engine for decades and disturbed from its slumbers.
A nice idea :) it might mean I could avoid taking ownership of what happened! Thank you for the suggestion.
julianharty
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Re: One step forward, then a brief clatter and the engine stopped

Post by julianharty »

mbmm350s wrote: 10 Jul 2024 09:42 Hi Julian,

Doesnt sound too serious. :)

Helicoil of plug threads should be fine.

Are you sure its an M6 and not perhaps an errant M7 from the rocker studs? These washers seem to have a bevelled edge and are generally a little thicker than standard form washers.

Might be worth removing valves on that cylinder and check they are still straight.

Anyway shouldnt be too much to get it fixed which is a relief.

Mark
Yes, I'll be removing the valves (and then risk not resetting the collets 100%, as a byproduct of that work :) )

BTW I use a pillar drill to help remove the collets. Paul Compton showed me the technique, I'll write a separate post on the technique with some photos.
julianharty
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Re: One step forward, then a brief clatter and the engine stopped

Post by julianharty »

Detail:
Here's how I fitted the engine to the frame; the rockers were on and the spark plugs were in by this point (the tip of the rear plug is just about visible)
Fitting the 250 2C engine in the frame.jpg
Fitting the 250 2C engine in the frame.jpg (489.49 KiB) Viewed 376 times
I've separate photos and videos for when the engine ran initially and then after I'd fitted the airbox and balanced the carbs. The engine ran well with no hint of a washer rattling within.
Steve Brown
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Re: One step forward, then a brief clatter and the engine stopped

Post by Steve Brown »

Blimey! You don't do things by half do you? I see you have ordered a kit to repair the thread-I have a 'Recoil' brand thread insert kit for 14mm spark plugs but I only read your news just now. The Recoil kit is a Helicoil clone, easier to use than genuine Helicoils and yes, for the spark plug thread it is self aligning and works very well. It also needs less parent metal removal than the Wurth types. Not sure how much spare material you have surrounding the plug thread left to play with.
You're welcome to bring the job here for a demo.
All donations to the rest home for old Camels, Leicestershire.
MickeyMoto
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Re: One step forward, then a brief clatter and the engine stopped

Post by MickeyMoto »

Not sure an M7 would fit down the spark plug hole being 14mm diameter, the same as the thread.

I used a timesert on a Laverda cam block thread. It worked well. However, I had to drill out the old thread, tap a new thread, screw in the new thread insert etc.
Steve Brown
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Re: One step forward, then a brief clatter and the engine stopped

Post by Steve Brown »

I agree the Timesert method is a good repair and as I think it is similar to the Wurth it does need more of a hole boring. With the Helicoil types it's only one (approx) thread size larger. As for the Recoil version I have, the tap has 2 cutting diameters. The first is a standard 14mm plug thread that is used to pick up on what's left of the original thread and align the main second diameter to cut the thread for the wire insert coil. I've used it dozens of times and it's never failed to align or make a good sound repair. I also prefer the fact the plug thread hole is not a lot larger and so less likely to weaken the head and lead to cracks forming.
All donations to the rest home for old Camels, Leicestershire.
3potjohn
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Re: One step forward, then a brief clatter and the engine stopped

Post by 3potjohn »

Sorry to hear of your woes.
I’ve used a spark plug thread insert ( from Unithread) on a beemer. Didn’t even pull the head off . I used a magnet to collect the tang from the insert and a tube down the hole connected to a Dyson to remove any swarf. As it was only soft alloy I was not too worried but think it all came out.
I’d be interested to know if you have a washer AWOL from the filter housing.
It’s a hell of a way to decoke an engine.
julianharty
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Re: One step forward, then a brief clatter and the engine stopped

Post by julianharty »

3potjohn wrote: 10 Jul 2024 20:28 Sorry to hear of your woes.
I’ve used a spark plug thread insert ( from Unithread) on a beemer. Didn’t even pull the head off . I used a magnet to collect the tang from the insert and a tube down the hole connected to a Dyson to remove any swarf. As it was only soft alloy I was not too worried but think it all came out.
I’d be interested to know if you have a washer AWOL from the filter housing.
It’s a hell of a way to decoke an engine.
Aye, to think I'd bothered to pre-clean the guts of the engine with a bead blaster, ultrasound, etc. If old nuts and bolts are good enough to clean a rusty petrol tank just think how efficiently we can clean the entire engine internals by feeding washers through the carbs! They just need to be small enough to fit past the exhaust valve at full throttle!

The filter housing is held on by 3 long M6 bolts, they're 80mm and 90mm long (I can't remember if it's 2 of 1 and 1 of the other, or the other way around). They have use flat washer. I'd reassembled the filter housing (which is held together around the edge with small M4 or even M3 bolts. There's nothing inside apart from a single air filter, so no obvious source of the M6 washer unless I'd somehow managed to drop it either directly into the small bellmouth of the rear carb or into the pair of rubber 90 degree air inlets. When I reassembled the bike I used one of the old M6 bolts and 2 new ones. I've checked again; the bottom of the airbox still has a washer under either the head or the nut as appropriate.

I've already removed the head and the valves and will clean them to remove the worst of the surface damage then they might enjoy a spa bath in the ultrasonic cleaner before I refit everything (apart from the crushed washer).
julianharty
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Re: One step forward, then a brief clatter and the engine stopped

Post by julianharty »

Steve Brown wrote: 10 Jul 2024 13:35 Blimey! You don't do things by half do you? I see you have ordered a kit to repair the thread-I have a 'Recoil' brand thread insert kit for 14mm spark plugs but I only read your news just now. The Recoil kit is a Helicoil clone, easier to use than genuine Helicoils and yes, for the spark plug thread it is self aligning and works very well. It also needs less parent metal removal than the Wurth types. Not sure how much spare material you have surrounding the plug thread left to play with.
You're welcome to bring the job here for a demo.
Steve, thank you for your generous offer. I've found there are several types of repair kit from recoil, the high-end one such as yours and available from RS components, etc. https://uk.rs-online.com/web/p/thread-r ... ts/2448268 and quite expensive (£110 ish) and a lower-end one typically around £45 - £60 depending on the vendor. I much prefer the stepped tap approach than using a large drill. There's an older kit for sale that looks like the predecessor in a metal box made in Oz for £60, or I might ping you and visit depending on my thoughts once I've received the US PRO kit. I'll let you know either way.
julianharty
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Re: One step forward, then a brief clatter and the engine stopped

Post by julianharty »

MickeyMoto wrote: 10 Jul 2024 15:28 Not sure an M7 would fit down the spark plug hole being 14mm diameter, the same as the thread.

I used a timesert on a Laverda cam block thread. It worked well. However, I had to drill out the old thread, tap a new thread, screw in the new thread insert etc.
Well spotted (unless the washer was pre-deformed) as the available width of an M14 x 1.25mm thread is 12.75mm. Even a 12mm washer would have to be lucky (and in turn me unlucky) to successfully navigate the deep plug hole (50mm before the entrance and then another 20mm or so through the threaded section). I also looked at whether it'd be practical for a washer to feed through the carb's slide and needle. Looks like both M6 and M7 washers could make it through the drawbridge.

There's much for me to learn through this experience :)
julianharty
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Re: One step forward, then a brief clatter and the engine stopped

Post by julianharty »

Another update :)

I'm a member of a local WhatsApp group of folk who avidly work on and ride older motorcycles and they routinely mill, lathe, and otherwise make and repair bikes and engines. I asked for their advice and have ended up with similar recommendations from that group as from this group, with backup options if my repair fails.

One of the key recommendations is to buy helicoil style inserts from WTI Fasteners who even sell a complete kit similar to the one Steve Brown has https://www.wti-fasteners.co.uk/product ... k-plug-kit They're a relatively old fashioned business, who take orders by phone. Prices are far better than many, roughly £45 + p+p for their kit including inserts for M14x12.5mm they have a double-stepped tap in their kit and an additional 10 helicoils is under £7 if I end up needing to repair lots of spark plug threads (let's hope not!).

So this is the route I'm going to take - helicoil as it using them removes less material from the head, and WTI fastener tools as the are well recommended and likely to be as reliable as the tool Steve uses.

More news once I've received the kit tomorrow. Hopefully the bike will be back on the road, rattle free, by the weekend :)
Steve Brown
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Re: One step forward, then a brief clatter and the engine stopped

Post by Steve Brown »

Sounds good to me!
All donations to the rest home for old Camels, Leicestershire.
julianharty
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Re: One step forward, then a brief clatter and the engine stopped

Post by julianharty »

MickeyMoto wrote: 10 Jul 2024 06:46 Ouch.

Careful when you remove the barrel in case any swarf is dragged down the bore. Might be worth oiling around the piston.
-- snip --
Your recommendation was spot on. I ended up using lithium grease in a layer around the circumference of the barrel and turned the engine over gently several times. The piston deposited various pieces of metal, some probably steel from the spark plug tip. I cleaned off the combined grease and swarf and repeated this several times until no new swarf emerged. I then removed the barrel carefully and with material to catch any more bits and pieces.

Then it was on to checking the piston rings and how cleanly they rotated in their respective groove. There was a grittiness so I've removed the rings and cleaned the grooves with a combination of a wooden toothpick, a fine interdental dental toothbrush, spray brake cleaner, etc.
swarf from the side of the piston.jpg
swarf from the side of the piston.jpg (489.01 KiB) Viewed 329 times
I've also honed the bore using a couple of inexpensive mechanisms. There's still evidence of vertical scoring however it's undetectable by my fingers and should be fine (I'll know more when I do a compression test).
Bore after honing it.jpg
Bore after honing it.jpg (319.25 KiB) Viewed 329 times
julianharty
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Re: One step forward, then a brief clatter and the engine stopped

Post by julianharty »

Short version: the engine is back together and seems to run acceptably without clattering. I've taken it for a short ride of 3km and we both survived. Now it's time to continue snagging and fettling it.

Old bikes can have their challenges though...
  • The super-duper helicoil kit worked (I might write this up separately).
  • ...But the resulting thread was tight and damaged the thread of a brand new NGK spark plug. I used the Sealey thread restorer tool (Sealey Ms003 Reverse Action Spark Plug Thread Chaser) to good effect, and fitted another brand new spark plug - still quite tight but it'll do until I've reason to investigate again.
  • It's hard for me to work out if the oil pump is feeding oil at the right pressure, etc. I ran on the drive the bike with the tappet covers removed, no obvious sign of oil being splashed up the pushrod tubes at low to medium revs. As I've lubricated all the components they've got oil, I'll keep an eye on this and am open to suggestions of how I can check the oil feed is working on the 250 2C engine.
  • Carburation is still fluffy around 4 - 5k rpm. I'll fit the air mixture screws from the 350's carb model (bought new from Eurocarb) as Mark recommended this in ATG222.
  • The front tyre (a new Continental) is reluctant to seat itself and causes vibrations when ridden. I'm trying some tyre soap, etc. and if I run out of ideas I'll ask my local bike shop to help resolve the seating of the tyre.
Attachments
sparkplug galled by helicoil.jpg
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