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plunger madel 7

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Hello Every one. 

This is my fisrt post so I hope this question has not been asked before. Does anyone know why my plunger model 7 handles ok when on twisty roads. But does not like going straight when on a straight road, it feels like there is a strong side wind that hits it in gusts. Also when slowing down from any speed above 30 the bike gives the feeling that the rear tyre is flat or there is oil on the rear tyre.  Horrible feeling, I have checked the plunger arangement and the front forks and so far not found anything wrong. Any ideas what is wrong.

On my last ride out with the local VMCC group a gent cam up to me and said the he had one and that it handled like s***.. anyone have any ideas why these are so bad. Or are there some that are OK.

thanks. mike

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Roadholder-forked, plunger Nortons won TTs and were considered by the riders to be better than the girder rigids which in their day were state of the art.

General wear won't help but it sounds as if there is something badly wrong with yours. I'd start with the easy stuff, assuming that you've given everything a good check for slackness and misalignment which will affect the handling of any motorcycle.

What tyres and pressures are you running ? Even modern old-fashioned tyres have modern carcases with soft side walls which will need much higher pressures than those specified in the 1950s.

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Hello Richard.

I bought this bike last year and it has modern type tyres Roadmasters front and rear. Ali wheels with later 8inch full width hub and 19 inch front wheel. Been playing with different tyre pressures from 25 psi to 34 psi. Found 30ish feels better for general riding but this does not change the NOT funny shake when slowing down which does not change weither braking or not. As for going along a straight road it is very tiring contantly adjusting for the bike wandering.

I have spoken to another owner only to be told this is normal which just feels wrong to me. This is the main reason for me placing this question. . mike

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Hi Mike

It should behave nicely as Richard says. I have a 1950 plunger but the ES2 version and it is perfect in a straight line. The only time the ride suffers is cranked over on bumpy bends and this feels wallowy because of the lack of damping.

I will give you a check list of things to go over, in the hope that this helps, which others can add to and improve on:

1. On the stand grab the rear wheel and try to twist it vertically, and at each 45 deg angle. There is unlikely to be any movement in the plungers because they are long pins, 12" or so, running in the aluminium housings. More likely is a worn rear bearing, or a bearing now lose in its hub because it has hammered a recess in the hub.

2. Put a block under the frame at the front to raise the front wheel off the ground. Check the headstock bearings by holding the bottom of the forks with two hands and pulling them forwards and backwards. Any sign of play means they need adjusting/replacing. But loose does not cause poor stability in a straight line. It is pitted or stiff bearings that will have you wondering all over the road. Do the handlebars turn smoothly with absolutely no notching?

3. While at the front check the wheel bearings by grabbing a fork leg and adjacent rim and seeing if you can feel any play.

4. It sounds like you have reasonable tyres and know about pressures. Are all the spokes good?

5. If you cannot find play in any of the above then you have to suspect a crack in the frame. Go over the big down tube above the gearbox especially with a good torch and look for any rust lines near castings. If it is oily it will need a though degrease. Take the tank off and check around the head stock.

Best of luck

Norm

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My 1952 ES2 with plunger suspension handles far better than I had been led to believe both in a straight line and cornering. Very bumpy bends can confuse it a bit but left to its own devices it soon recovers.

The wandering when going straight is particularly surprising as mine has a strong self-centring action.

Just a thought - you are sure the steering damper is fully slackened off as this can cause that type of fault?

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Have you checked to see that perhaps the last time the wheels were rebuilt they were not centered?

Mike

I have checked the wheels, frame and forks and not found any faults. Changed the oil in the front forks just to know what oil they had in them. Have had to adjust the headstock bearings three times these were very loose when I bought the bike and I will remove the forks in the next few weeks to check the head stock bearings. Reset wheel alinement after each headstock adjustment. Strange handling has remained the same.

Thinking of sending the frame to be checked just to make sure it is not bent.

Thanks for answering my question about the bad handling at least I know something is wrong just need to find out what it is.  Mike

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I've got the ES2 version of your bike and like others have said, it handles.... OK. I've been told that those frames do break though, it's not common but it does happen. Check the seat downtube around the gearbox mounting and the main spine under the tank near the rear tank mount. It's unlikely but your symptons sound quite dramatic. I had a Royal Enfield Continental GT that suddenly started weaving and wobbling, turned out the frame was snapped under the headstock.

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to need to adjust steering head bearings more than once - they should stay adjusted for ages. That's where I'd be concentrating - maybe a bearing race is misaligned or a seat is distorted / damaged.

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I agree with Ian there...head bearings are a 5000 mile check sort of item with the odd pump of grease in between...any adjustement would be minimal...Damaged threads and botched repairs need checking for in that area...Owners are capable of the most remarkable 'repairs'.Some of them are serial restorers too, never living with each completed bike long enough to sort it.There is a WD16H on eBay at the moment with a welded fork side link and a spindle nut barely hanging on...

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Another plus for Ian and Richard. My featherbed Dommie felt horrible for a while until I slackened off the head bearings a tiny bit. Back felt like jelly for a while. I'm no expert on suspension but I thought I read that if the back end feels wrong, it's usually a fault at the front.

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.. my Guzzi V50 it nearly spat me off at the first roundabout. It fell into corners and wouldn't hold a line. On lifting the front I discovered the steering head bearings were bar tight - I had to back the adjuster off at least half a turn to get anything like free movement. After that it steered like a dream (but not a Norton!)

Fortunately the bearing races hadn't brinelled so I didn't need to change them - not a job I enjoy.

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Thanks for your replies. Im pleased to hear that the handling should be better and less unpredictable. I agree that the headstock should not need adjusting so many times and have already decided to strip the front end. I need to do a respray on the front mudguard anyway.

 

Has anyone fitted tapper  roller bearings to the headstock on this model and was it worth the hassle. thanks mike

 

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