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What would cause intermittent heat seizing? I've managed it twice recently. Both under identical conditions, on a warm day with the engine under load on a gradual climb. Yes, I know that sounds pretty self explanatory. But, I've used it in similar conditions on worse hills and it hasn't missed a beat. I know air leaks are often the cause. But wouldn't that mean it consistently overheated?

Spec wise the engine is nothing wildly exciting. Just a plain old 200 with a Scootopia carb and Ancillotti clubman.

Jetting, ignition timing, fuel flow, plug heat range, suspect fuel, piston/bore tolerance, etc...

Hi Adam.

Jetting seems to be there with a healthy colour on a B8 plug. It's a Scootopia fuel tap and there seems to be a decent flow through. But yes, it needs to come apart properly and the timing has got to be a suspect. Piston to bore tolerance, could be. Although it was remarkable for not even being marked after the first time. Perhaps that lulled me into a false sense of security. I did actually reuse the fuel in another engine and it didn't cause any problems. Although, admittedly that has an alloy barrel and would be cooler anyway. I should really have had a proper investigation the first time around. Time to get it properly sorted I think.

When you say timing suspect, did you initially set it up and if so how advanced was it ?
Are the Clubman and/or the Scootopia carb recent replacements ?
The plug colour, was that immediately after the heat seize or when you got back home ?
Petrol octane and petrol integrity is not to be messed with unless your timing advance has been reduced appropriately.

Just to clarify. I don't know that the timing is suspect. Just that it is usually a suspect in cases like this. So, it will be checked. I didn't build the engine myself I'm afraid.

The exhaust is not so recent. Although the tap and carb are. From memory I checked the plug after the initial seize and it seemed a little dark, if anything. Although, the second time I didn't bother. It seemed academic, as I had to nurse it home anyway. The one thing that does occur to my untrained mind is the oil percentage. I was actually running on 4%, which I understand runs hotter than 3% and on a hot day might have tipped it over the edge. Maybe there is a lesson to be learned there? If nothing else this is helping me to formulate an idea of what I want to do with it.

4% will not be the issue. Plug colour is only an indication of what it was running at before being checked, it cannot be used to determine whether your jetting is good across the board (e.g. rich at half throttle but weak at full throttle, etc.).

Ignition timing is a key factor... a pal of mine did thousands of miles at 16-17 dbtdc (set by me as that it what the motor had determined was required, compression, porting, etc.) but my pal then had it stripped and rebuilt by a.n.other for the seals to be changed as a matter of course. This 3rd party 'corrected' the timing to 19 dbtdc and the bike immediately ran into seizure issues, which (following the resultant piston strip and replacement ) was instantly cured by returning to previous timing (the reduced advance on this iron barrel 175 was almost certainly required because of the high compression that typically results from many dealers supplying 175 heads that are simply 150 heads opened up to 62-63mm, without reworking the combustion chamber for 175 use, hence any standard 175 settings cannot be used). NB: Book values for ignition timing requirement are a starting point... the motor will determine what it needs to run well on the configuration of build.

Any time a motor seizes for unknown reasons I'll double check ignition timing as the first step of resolving issues. If in any doubt I'll retard the ignition a couple of degrees and then test accordingly, looking for other causes as I do so.

Good luck.

Adam

There was a slight clue in your first posting. You said it always managed hills under load without a hint of a problem but now it has heat seized it twice. So something has changed in the meantime. Anything ?

Too much Christmas pudding...........

Unread postby ToBoldlyGo » Sun Jan 29, 2017 2:41 pm

Hi Adam.

Jetting seems to be there with a healthy colour on a B8 plug. It's a Scootopia fuel tap and there seems to be a decent flow through. But yes, it needs to come apart properly and the timing has got to be a suspect. Piston to bore tolerance, could be. Although it was remarkable for not even being marked after the first time.

This is just a thought, but have you got a good, clean air filter? If the engine's not getting sufficient air, it starts to 'stall' which very closely resembles a heat seize as power dies.

I've had this happen many years ago running an Amal Mk 1, on shortened manifold, through a drilled air filter box. It ran fine until you gave it some stick, which is when the problem would occur. In my case, the drilled air-box exasperated the situation (with hot air being pulled in, getting dirty quicker) but the filter was simply not adequate for the 30 mm carb size.

I'd also be very wary of the soft bellows sold these days, made of black snot, that can be seen to collapse when revving on the stand.

I know, I've seen that WT1. Indian bellows are the problem. An interesting point about the air filter none the less. It's a washable type and should have been clean'ish.

CHRIS in MARGATE wrote:There was a slight clue in your first posting. You said it always managed hills under load without a hint of a problem but now it has heat seized it twice. So something has changed in the meantime. Anything ?

Ah, I think I know where this is going. The carb and tap were changed prior to the initial seize. I'm not going to cast the blame just yet, until everything has been looked at. We could be giving a dog a bad name. But yes, it was up hill and down dale. Of course the underlying problem could have been there none the less.

MickYork wrote:Too much Christmas pudding...........

In August!

But it's January !

Unread postby ToBoldlyGo » Sun Jan 29, 2017 7:27 pm

MickYork wrote:
Too much Christmas pudding...........


In August!

Any pudding is for life, not just Christmas!

Especially the King of Puddings: Bread & Butter Pudding

I think we need to establish which pudding has been eaten before we can diagnose the fault......if it was August I cannot see salad being the cause

I agree. Establishing the precise pudding is crucial.

But, there is a reason for the discrepancy. I wasn't working at the time, so the scooter had a good telling off and was resigned to the garage. I am now, so it's time to get the ball rolling again.

All Lammy's require tuning in such a way that they don't produce too much piston heat as indicated by the advice above.
They also require an effective forced air cooling system that works properly irrespective of weather conditions.
Iron cylinders, lightweight heads and some piston makes are particularly susceptible to seizure due to poorly engineered cowlings.

Re: Head cowling improvements
Postby Warkton Tornado No.1 » Mon Jan 16, 2017 9:15 pm

Postby Fast n Furious » Mon Jan 16, 2017 7:37 pm

Photographs mmmmm.
My camera makes pictures that are 5+Mb jpeg which are too big for posting I think. I need to find a way of condensing these into something more manageable. When I've figured that out I post some pics.


Dropbox is available free & a hassle free way of adding files, IMHO. (https://www.dropbox.com/en_GB/)

BTW, the longer response of yours (detailing your analytical approach to improving head cowlings) makes for excellent reading.....
Warkton Tornado No.1

Posts: 791
Joined: Sun Jan 11, 2015 1:27 pm

Re: Heat Seize
Post by Fast n Furious » Mon Jan 30, 2017 2:48 am

All Lammy's require tuning in such a way that they don't produce too much piston heat as indicated by the advice above.
They also require an effective forced air cooling system that works properly irrespective of weather conditions.
Iron cylinders, lightweight heads and some piston makes are particularly susceptible to seizure due to poorly engineered cowlings.

With respect, I think we are all waiting to see how you achieved that....

Could be a " Cold Seize".
Where do you keep your Scootter?
If it is in a cold enviroment, i.e,cold unheated garage/shed or even worse outside in the sort of weather we have been having what can happen is that the piston, being made of aluminium heats up and expands a lot quicker than the cast iron barrel. In the worse case scenario the engines seizes !

The answer is to thoroughly warm the engine before putting it under load

your problems could well be many of the things mentioned above, adam mentioned that your plug colour is only an indication of your mixture, and he is right, its not easy to read a plug, or to do a proper plug chop, you should simulate the conditions it siezed in,best plug chop is uphill full throttle and held there , your fuel mixture is the biggest cooling factor on your engine, too lean and your in trouble, hills put your engine under more load so you will open the throttle more to compensate, i would check your flow of fuel out of your fuel pipe first, then i would do a leakdown test, next strobe your timing, when all that is ok i would check the jetting, i normaly over jet a carb til it bogs on full throttle, then come down in size til it wont bog anymore and you should not have any more nipping up, you wont get max power this way but your engine will be safe at full throttle, i would also check and maybe increase pilot jet as well,
good luck,
holty

were you wringing its kneck up the hill/incline or just on half throttle?
when you say Scootopia carb is it a sh2/22 version?
how far into your ride was it?
& I prefer rice pudding.....

ROClarke wrote:Could be a " Cold Seize".
Where do you keep your Scooter?

The answer is to thoroughly warm the engine before putting it under load

My garage isn't great and certainly not heated. Although, this was in the summer. I agree, I always warm up a bit before the off and never thrash it until it's properly warm. You could tell my initial seize was heat induced. You could feel it get really hot.

holty wrote:your problems could well be many of the things mentioned above, adam mentioned that your plug colour is only an indication of your mixture, and he is right, its not easy to read a plug, or to do a proper plug chop, you should simulate the conditions it siezed in,best plug chop is uphill full throttle and held there , your fuel mixture is the biggest cooling factor on your engine, too lean and your in trouble, hills put your engine under more load so you will open the throttle more to compensate, i would check your flow of fuel out of your fuel pipe first, then i would do a leakdown test, next strobe your timing, when all that is ok i would check the jetting, i normaly over jet a carb til it bogs on full throttle, then come down in size til it wont bog anymore and you should not have any more nipping up, you wont get max power this way but your engine will be safe at full throttle, i would also check and maybe increase pilot jet as well,
good luck,
holty

Good advice. Hopefully it'll get a good seeing too. There is one thing that I actually neglected to mention. Although not deliberately. The second seize was accompanied by a squeaking. So something was awful dry. I suspect a bearing. The wonder of it is it still ran afterwards. Although perhaps it wasn't the best of ideas.

hullygully wrote:were you wringing its kneck up the hill/incline or just on half throttle?
when you say Scootopia carb is it a sh2/22 version?
how far into your ride was it?
& I prefer rice pudding.....

Me, wringing it's neck? No, it's a good long hill and it seemed to be struggling more than usual. It was about 15 miles into the ride or so.