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D14 engine seizes as soon as a little warm
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Roarn
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June 8, 2020 - 4:49 pm
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My friend has restored a BANTAM D14/4 175cc 1968 here in Norway, probably one of very few, if not the only one and he has major engine problems to be solved, after restoration - piston warm sized 3 times  -  when driving a litte hard! (not very hard)

Rebored cyl / new piston after restoration and as soon as he started drive it sized when warm, it was honed and sized again. Then got BSA BANTAM 64.5mm big bore piston set from
rexcauntracing, rebored at another workshop and installed - same happened AGAIN. Bought a 3rd new piston set and mounted this spring, no real wear marks to cyl liner, looked good , just honed it and put it together and after a little while it warm SIZED.

He has installed a electric ignition kit too it, and have a problem to fine tune timing?

 

Does anyone has some good advice, he has put a lot of hours and £ into this now very nice none working Bantam,

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Stoo63
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June 8, 2020 - 10:08 pm
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Hei, Roar and welcome to the forum. What a dreadful run of bad luck. Hopefully some of our members will have some advice for you and your friend.

You will find just about everything you could ever want on the Forum via the FAQs and technical sections;  ** Please log in to view **

Have a good nose around the forum and enjoy yourself. Hopefully your friend's bike will be zooming around the fjords before too long 🙂

Good Luck!

All the best,

Stewart

 '55 D3 Battery; '58 Square Four (project); '59 D1 direct lighting plunger; '59 Tiger Cub; '60 5TA;  '76 FS1-E; '91 GTR 1000;  '97 Honda Sky SGX50.

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stubaker58
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June 8, 2020 - 11:18 pm
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Hi Roarn,

Sorry to hear about your friend’s problems.

Can I ask how much oil is he putting in the petrol? I use 175ml per 5 litre with no problems.

Regards,

Stuart

D7/14 hybrid (4 speed with D7 crank etc.) on the road, D10 Bushman awaiting rebuilding.

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wildun
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June 8, 2020 - 11:31 pm
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Are you actually mixing two stroke oil with your petrol ? 40ml of two stroke oil to one litre of petrol = BSA manufacturers recommendation of 25:1, or 4% as you continentals measure it. ( not 175ml, stubaker58, that is about 5 to 1 !! ) 200ml of oil into a 5 litre container of petrol.

I would almost say that I cannot believe that this is happening to you every time.

For your engine to overheat so much so quickly then the ignition timing would have to be a very long way out.

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nickjaxe
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June 8, 2020 - 11:34 pm
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Very odd Roarn.

There has to be a clearance between the piston and the bore...has you pal checked it.

If the machine should have re-bored it to tight it will never work....the bore need measuring and the piston....at the correct place on the piston...were did you pal buy the Piston...if its from Rex in the UK the clearance is marked on the box.

Next is the piston the correct way around....and importantly...are the port edges been radiused to take the sharp edge off.

The other thing that can seize a piston is it the fuel/air ratio is to lean....the incoming petrol change need to be slightly rich to cool the piston.

Its also possible that the timing is way out if your having problems with the electronic ignition....what was wrong with the std system....so easy to set up and keep running....noting complicated.

Dont be offended but I have to ask as I don't know your experience level.....but is your pal putting 2 stroke oil into the petrol and at the correct ratio?

Would not be the first time I have come across somebody has no idea about engine lube and 2 strokes....as I say goto ask.

One more thing....not every engine shop does a good job of re-boring 2 strokes...everything needs measuring to be sure.

Nick.

My Bantam video              https://www.you.....jpOFmzRZRI

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Roarn
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June 10, 2020 - 3:39 pm
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Hi again!

Thank you for all input / thoughts to solve the mystery, I will try to give a little more info about the owner and the Bantam. Owner is a very good friend of mine (with little English writing nor computer skills ,,, ) age 62 and worked all his life as car mechanic / bodyshop repair / painter and last 25 years certificated buss mechainc. He has always been into British cars, cofounder of Nordic Morris Minor Club about 40 years ago, still restoring Minors, (now an old cab) over years different cars on his hands like Rover P4 P5 SDI Mini Marinas Allegro MG F and so on. He also has a passion for 2 stoke mopeds and involved in local club. When he found this Bantam 6-7 years ago he fell for it - a British 2 stroke,,,, ultimate,,

It  - this 1968 Bantam  - came to Norway with a student returning home from studies in London maybe more than 20 years, it was his daily driver during his years in London, and it broke down on his way home,,, an put away as a none runner until my friend bought it. 

It was restored during a couple of years, he fitted a Electrex electic ignition with charging to it, but when restored it was a very poor driver, did not run properly and were concluded with worn out Amal carburetor. A new replacement (should be the correct for this?)  Amal 626 (R12) were soured and fitted, after that it run much much better. 

BUT then the piston/cyl issue started, when driving a litte hard it warm sized after 1 km, cooled it down started again but same issue and of course it did not do it any good. He thought the shop had done a mistake / faulty re bore and next winter he bought a new larger piston, went to a different engine shop (who previously done engine / cyl head work for him on cars) with same result. This winter a 3rd attempt, AND it still has the same problem (were stopped as soon as he understood and not driven afterwards)

Obviously its something he is missing in his frustration, petrol / oil ratio should be ok, piston clearance might be an issue but since 2 different machine shops has been used with same result, we might think its not, or? Pistons always from Rex Caunt Racing (as most other parts). Might it be the air / petrol ration, problems with adjusting the new carburetor that is the reason?  Is there someone who has a guidance to basic adjust, or how he set up this carburetor correctly?

I will try to add some pictures of it very soon!

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Blue Heeler
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June 10, 2020 - 3:54 pm
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Thanks for the history.

Ignition timing & or fuel-air mix.

Did he keep an eye on the plug colour? If so, what was it. What make & grade spark plug is fitted?

I advise check for air leak between carb and barrel.

Jets, needle in carb all need verifying.

Long shot, but very occasionally bores distort when hot, due to casting anomaly.

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nickjaxe
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June 10, 2020 - 4:29 pm
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I know a guy who had very similar trouble...seems in the end after lots of expense and head-scratching....that his engine had the wrong head on it....the compression ratio was too high....its was seizing in a similar way.

Also check the barrel is the correct one to match the head.

But I would also when stripped again be checking the piston to bore clearance....don't just trust the workshop.

Also just because your piston has seized...it doesn't mean the piston is scrap....or it needs another re-bore....it depends on damage....just a scuffed position can be work with a light file to take of the seized high spot....in the direction around the piston...not up/down.

Of course, is the piston is very bad or the bore scored that a different matter.

Is he being gentle with it during its running-in period????

Nick.

My Bantam video              https://www.you.....jpOFmzRZRI

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Pootle
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June 10, 2020 - 5:03 pm
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I had a similar problem with a B175 with a new carb, I found I needed to raise the needle and go up to the next main jet.

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cocorico
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June 11, 2020 - 10:03 am
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Hello Roarn.

To try to gather the suggestions already made from amongst the reminiscences of days gone bye:

Check the bore size, the piston size, ring gaps and their location pins.

If there are scuff marks on the piston, see if they can be removed with a fine file, likewise inspect the cylinder for gouges, perhaps give it a light hone (a honing tool is very cheap from ebay /Aliexpress, etc).

Re-check timing settings - I don't have a D14 but I think that version is a bit particular on timing.

Ditto petroil mix and carburettor settings.

Perhaps restore the original points and coil ignition if it's still available - electronic ignition doesn't cure underlying problems.

Once running, use gentle runs to bed everything in - a few revs up and down the gearbox to ensure the engine is not overloaded.

There is a D14 Workshop manual, etc here, in case you don't have one. ** Please log in to view **

If you have already carried out all of the above - start over again, one by one, it has to be something basic to cause a seize.

 

For other members - this is to try to be a bit clearer to someone who is not using his home language, so may find some of our terms puzzling, we do 'carry on' a bit sometimes.

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Sponge
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June 11, 2020 - 10:28 am
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I have a great deal of sympathy with this thread having been in a similar situation after a re-bore myself. 

I have found that with a fresh re-build, or top end work, there is a chance that several things are wrong and it all manifests itself. Especially with the D14/4 which was renowned for overheating due to its top end tune.  Without seeing the engine it is difficult to diagnose but I suspect the problem can be mitigated by running through the checklist below - leave nothing out and good luck !!!  old Military saying - "if it hasn't been checked - it hasn't been done !!'   

Checklist:

Confirm the age of the crankcase seals ( these may be old, going stiff and leaking a bit of air ) this would cause the engine to over heat etc  

Measure cylinder bore in several places, with piston in and with piston out, and make notes - rectify as required to bring into tolerances  

Ensure all the fins on the barrel and head are clean and free from obstructions - mud, grime etc  

Remove the fairing and leg shields ( if you have them fitted) 

Check that nothing is preventing airflow around the engine.............   

All cylinder ports radiussed ( all sharp edges taken off after rebore ) ***

Piston clearance set as specified by the piston supplier

Piston ring gaps correct (rectify as required) 

Piston fitted correct way around - pegs forwards 

Check for air leaks at base flange, cylinder head and carb flange joint. Rectify as found. 

Use fresh high octane fuel ( modern low octance, lead free stuff can cause overheating, old fuel will cause overheating ) * 

Use correct 2T mixture (specified for pre-mix) and add a bit more for running in as per manufacturers instructions   

Set ignition timing / points as accurate as possible 

Check carb settings are as per book and rectify as required

Check that air filter is present and not blocked (clean it out if necessary)  **

Check that exhaust is correct and not blocked (de-coke it if necessary) *** 

Check there is clean oil in the gearbox.  

Check that the brakes are not binding with a rider on the bike ** 

Always warm it up before you ride it - until running in is complete.   

Ride it very light and easy (with a lightweight rider and no pillion), for first few hundred kms.   

If all that doesn't clear the problem and the bike is still running hot then try running with two head gaskets (to lower the compression ratio a bit during running in ) and then come back to this forum for new ideas. 

Some photographs would help here. There are some very experienced forum members and club members on here with eagle eyes who might just spot a clue and have a solution.  A picture of the piston and bore might be very useful to them.  

Sponge

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Roarn
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June 11, 2020 - 6:44 pm
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Hi again!

Lot of good inputs here - will add some info and good pictures the coming days. 1st picture unrestored 2nd & 3rd after restorationIMG_0038.JPGIMG_07399.JPGIMG_07400.JPG

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Blue Heeler
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June 11, 2020 - 8:07 pm
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Puzzling, should run nicely with the centre plug B175 cylinder head he has fitted there. Mine certainly did.

B175 barrel too? Can you provide the the first part of the engine number please? The B175 has a 4-stroke carb if my memory serves. Certainly a different carb for B175s to the D14s I own. Your mate`s engine should be under a lot less stress than a D14, so something must be way, way out for it to be experiencing the issues it`s gone through. 

Hopefully you can thoroughly check the 4 main potential issues, covered above in detail and rule them out one by one.

1)Engineering tolerances

2)Ignition timing & plug grade

3)Fuel & air mix, carb clean. Jets& needle.

4)Possible air leaks

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Roarn
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June 11, 2020 - 8:25 pm
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I will help my friend with all this info, he has realized he has to take 2 steps backwards and eliminate all possible issues, dont think the REX pistons is an issue, dont blame them sine these 3 different pistons were bought during 2 years.  

 

Spark plug used NGK BP7 ES - head gasket used are 0.05mm (thinnest supplied in engine gasket set 🙁 )

Cylinder port edges are sharp, probably not radiussed

IMG_074888.JPGIMG_074999.JPGIMG_075000.JPG

 

Here is picture of needle and position - then jet with numbering written.

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Blue Heeler
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June 11, 2020 - 8:33 pm
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Roarn said
I will help my friend with all this info, he has realized he has to take 2 steps backwards and eliminate all possible issues, dont think the REX pistons is an issue, dont blame them sine these 3 different pistons were bought during 2 years.  

 

Spark plug used NGK BP7 ES - head gasket used are 0.05mm (thinnest supplied in engine gasket set 🙁 )

Cylinder port edges are sharp, probably not radiussed

IMG_074888.JPGIMG_074999.JPGIMG_075000.JPG

 

Here is picture of needle and position - then jet with numbering written.  

*****Ah, there we are, non radiused ports, sort that and all should be good! ***** This procedure is critical for safe running of a two-stroke engine. I rebuilt several trashed engines that the owners had failed to carry out this job. 

Jets sizes look ok, but if in doubt go up one on the main jet. Needle position ok. Plug`s ok at a 7 grade.

With running the centre plug head, don`t worry about head gasket only being .5mm. That is what you meant, yes, not .05mm? B175 has lower compression ratio than the D14. 

Double check that carb model is ok for a B175, if that is the full engine designate, not just B175 parts fitted to a D14 engine. As mentioned in previous post, please check engine number for confirmation.

The B175 is in a mild reliable state of tune with better combustion and cooling to a D14, thanks in part to the centre plug head, so hopefully, after you`ve taken off those sharp port edges that chop into the rings, honed the bore, cleaned up the piston, fitted new rings, you will have a nice bike 🙂

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nickjaxe
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June 11, 2020 - 9:23 pm
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If the place that re-bored the cylinder have not radiused the ports....I would worry about the std of the work....I check it out inc having the bore measure to check piston clearance....think you need to start with a clean sheet here.

I keep telling people....not all engine shops know how to re-bore a 2 stroke properly...ask me how I know.

My Bantam video              https://www.you.....jpOFmzRZRI

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Sponge
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June 12, 2020 - 11:43 am
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All agreed and fully confirmed - also with bitter expereince. Port radiussing is a must here, especially a D14/4.  My theory is that a narrow sharp edge (especially on the exhaust port) will get hot and start to glow to the point where it 'picks up' the softer alloy of the piston skirt and you get a partial sieze. 

Remove and round off those sharp edges ( not too much), and you make it unlikley for this to happen during normal road use - the heat just goes out of the exhaust.  So long as the exhaust is correct and unblocked it will exit quite happily. 

I wonder if its a good idea to remove a baffle during running in - Any thoughts ??

Sponge 

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Stoo63
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June 12, 2020 - 12:46 pm
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I think, Roar, tat it would be really helpful if your friend could provide us with some pics of his cylinder and piston.....

 '55 D3 Battery; '58 Square Four (project); '59 D1 direct lighting plunger; '59 Tiger Cub; '60 5TA;  '76 FS1-E; '91 GTR 1000;  '97 Honda Sky SGX50.

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nickjaxe
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June 12, 2020 - 12:48 pm
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I would say leave it in Sponge.

No extra oil as it needs to bed in...keeping the revs down....but briefly giving it the beans after an hour of gentle running.

I would still strip the barrel off and check out all the clearances...

My Bantam video              https://www.you.....jpOFmzRZRI

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Blue Heeler
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June 12, 2020 - 12:59 pm
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Very good point about the exhaust port Sponge...that and the oily carbon of a two-stroke. 

Re operating sans baffles, you`ve opened up a real can of worms there and I`m not playing, hehe...but be our guest & report back 😉

Someone mentioned extra oil. Extra oil through the jets means less petrol, which equates to a leaner mix.

Blue

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