Author Topic: A7 nip up  (Read 534 times)

Offline cznorbert

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A7 nip up
« on: 29.06. 2021 14:59 »
hello

Yesterday the engine seizure in my A7 plunger engine.  *sad2*
The wheel locked up for a moment and then I slowly rolled out and stopped. It was able to start, oil was seen returning to the oil tank.

Since then there has been a huge crank throttle, video of it:

https://www.youtube.com/watch?v=WW_CY4FITck


Could the piston rings be damaged? I'll have to take the cylinders off.

I would appreciate any advice.


Online Greybeard

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Re: Re: Can a duff magneto cause engine seizure?
« Reply #1 on: 29.06. 2021 15:35 »
I'm sorry this has happened.
The smoke from the chain case tells me that piston rings are not sealing, probably broken. Take the top off but before you pull the cylinder block right off the pistons stuff rag around the crankcase mouth to stop bits of piston ring from dropping inside.
Greybeard (Neil)
1955 Golden Flash, sprung frame
Supporter of THE DISTINGUISHED GENTLEMAN'S RIDE https://www.gentlemansride.com

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A Distinguished Gentleman Riding his 1955 Plunger Golden Flash

Online Greybeard

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Re: Re: Can a duff magneto cause engine seizure?
« Reply #2 on: 29.06. 2021 15:37 »
It would be better if this was a new post in 'engines'. Mods, will you scoot it over please.
Greybeard (Neil)
1955 Golden Flash, sprung frame
Supporter of THE DISTINGUISHED GENTLEMAN'S RIDE https://www.gentlemansride.com

Warwickshire UK


A Distinguished Gentleman Riding his 1955 Plunger Golden Flash

Offline Swarfcut

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Re: Re: Can a duff magneto cause engine seizure?
« Reply #3 on: 29.06. 2021 18:37 »
That's a Longstroke Motor and  on the YouTube Viddy its sounds almost as if the primary chain is running dry. There should be oil in there! There is a lot of mechanical noise and oil fumes from the tank. It's running very hot.

    If oil is returning to the tank as normal, the blue haze from the primary indicates either a very hot chaincase, (lack of lubricant) or piston/crankcase blowby via the drive side main bearing.   Longstroke models do not have an oilseal, but an oil slinger instead. so not a perfect seal and so communication between crankcase and primary case is possible.  Theoretically the chaincase can be emptied by the scavenge side. If it is blowby, combustion gases will also emit from the engine breather  and  also, if one of the caps is removed, from the rockerbox. Then as GB suggests the problem is with the bores, pistons and rings.

 Worth taking off the sump plate and look for any evidence of anything wrong.  Check  primary chain adjustment and oil levels and see how it sounds.

 Swarfy.

Offline cznorbert

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Re: A7 nip up
« Reply #4 on: 03.08. 2021 19:01 »
The damage to the seizure has been repaired.
New rings and cylinder honing were needed. Turns out it was a run-in, that's why it was seizure, I didn't take care of it.


Offline cznorbert

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Re: A7 nip up
« Reply #5 on: 03.08. 2021 19:02 »
However, I noticed a strange oil change. Oil from the primary case is transferred to the engine oil tank. I filled the oil in the primary case as described until it appeared at the bolt hole.

Offline cznorbert

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Re: A7 nip up
« Reply #6 on: 03.08. 2021 19:06 »
Is there flow through the bolt holes to the crankshaft ? If the seal is bad, broken.
Does not appear to be.
Or what could be the oil path?
Thanks for any ideas.


Offline cznorbert

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Re: A7 nip up
« Reply #7 on: 03.08. 2021 19:18 »
I mean the leveling screw hole, marked in red.

Online Triton Thrasher

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Re: A7 nip up
« Reply #8 on: 03.08. 2021 20:05 »
Insufficient piston to bore clearance and weak mixture are the commonest causes of piston seizures.

Labouring the engine at low rpm is a pretty common cause too though.

Offline Minto

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Re: A7 nip up
« Reply #9 on: 04.08. 2021 00:45 »
That level plug got changed later on to a lower one so you need less oil in there. Though that is possibly the least of your worries. Hope you get it all sorted ok
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Offline cznorbert

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Re: A7 nip up
« Reply #10 on: 05.08. 2021 06:49 »
In the picture I have marked the oil level in red, according to the manual.

 I don't understand, at this level, where does the oil pass to the crankshaft?

Offline Swarfcut

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Re: A7 nip up
« Reply #11 on: 05.08. 2021 07:24 »
Norbert. The early design of engine does not have an oilseal on the crankshaft. Instead there is just a large washer, we call this an oil slinger, so not a perfect seal as mentioned in my earlier post. For now I would set the oil level in the chaincase as normal, use the bike and see how much oil is being lost from the chaincase. We assume it is not simply leaking out. Make sure there really is a problem, not just things settling down after the rebuild. Use a simple wire dipstick and check the level on the cold engine after standing, preferably overnight.

 If there proves to be something wrong and oil is actually leaving the chaincase,  the most likely cause is that the slinger washer (Described as a Bearing Shim) is missing, the drive sleeve is the wrong one or the crankcase is damaged. To inspect this the cush drive and drive sprocket need to be removed. The drive sleeve should match the crankcase very closely, and with the drive sleeve pulled from the crank, you should see the washer, not the ball bearing. Your video had lots of crankcase oil fumes from the chaincase, so there is an obvious connection somehow between the crankcase and chaincase.

 The oil level setting on later models was lowered to help prevent oil getting into the clutch.  The chaincase cover simply has the cut out to set the level moved to a lower retaining bolt position as shown in published data.

 Swarfy.

Offline cznorbert

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Re: A7 nip up
« Reply #12 on: 05.08. 2021 08:43 »
Sorry Swarfy, I read your post of course but did not reply.

The oil does not run on the floor, unfortunately. That would be the easy way out.

 I tested it, measured it, twice. I adjusted the oil level so that the lower chain side was half submerged in oil, I could see this through the check window. After half an hour of riding, (max. 70 km/h), I couldn't see the oil. On the other hand, the oil level in the engine oil tank had risen about 10mm.

So I was looking for the place where the oil goes into the crankcase.

I will check behind the small sprocket to see if the 67 349 washer is there.


Offline Swarfcut

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Re: A7 nip up
« Reply #13 on: 05.08. 2021 09:02 »
 Norbert. You may be filling the chaincase with too much oil. The oil level needs to be  just deep enough for the chain to dip into the oil under the clutch chainwheel. The easy way is to drain the chaincase, start the engine and then add oil as the engine ticks over. When the chain starts to dip into the oil, a stream of oil drops will be seen through the filler hole flicking off the chain. Add just a little more for good luck. Then let it all cool down, check the level with your home made dipstick. After your usual ride, all cooled down, check again. All gone? You have a problem. More or less the same, that's fine, just keep checking from time to time, some slight loss is acceptable with the early type oil slinger design.

 Swarfy.

Offline cznorbert

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Re: A7 nip up
« Reply #14 on: 05.08. 2021 10:10 »
I see, I probably added more oil than your description says I should have. But it sounds very good. Thanks for the advice.

However, this is a lot less oil level than the red level indicator screw sets, is that not a problem? I mean cooling in particular.

But I have already removed the primary case, I think I will check the oil slinger. It looks easy job. Just to get a good night's sleep.