Saving Old Seagulls

Charles uk wrote:Bruce did I make a mistake in my spelling?

No spelling mistake Charles.................................Some levity on my part with the FFFFFFFFFFFFFFs.

I have ordered some replacement MSD Timing tape locally. I will get my FVP power head together in one bit to do a timing check this weekend.

I am happy with that because I need the incentive to do a pre assembly with it anyway. Speeds up the completion so cool.

I can get the other drive tube into the Shiners as well while I am at it....................yes, I have been somewhat procrastinating.

B

I've had a suggestion from one of our members where the error might come from, though I'm not sure if I can get my head around this.

A timing light with the dwell circuitry for a 4 stroke motor is set up for a spark every 720 degrees so the dwell angle displayed will be altered to suit the fact that it's only measured for 1 revolution, 360 degrees, this calculation could be confused by a spark every 360 degrees, giving an answer that is twice the correct result.

My logic would seen to say you'd only get half the correct reading not twice?

I think that we shouldn't concentrate on the possible errors that a strobe light might be giving, just because we are not comfortable with the end result. That is not to deny that errors could be present - we are measuring, and errors (large or small) are always present.

My strobe light is an old simple one (certainly suits me!) giving one flash per one spark.

An alternative low tech method, which is not highly accurate, is of course to observe when the points start to open. This should be accurate enoughto show whether the advance is 50, 40, 30 or 20 degrees and possibly more accurate than that.
Of course, this method is denied to owners of electronic systems.

The reality is that three FV/FVPs have been measured by three different people with three different pieces of equipment with all the results in the 45 to 50 degree range. Further measurements on more engines will either increase or decrease the confidence in these values. So please measure and report.

Jeremy

Has no one thought of checking the 50 degree result by static timing their engine.

Simple battery and bulb.

Works well on my old landrover.

I would expect the timing to be between 19 and 27 BTDC.

Will have a go at one of my engines and see what I get.

H-A

Hi guys,

I hadn't showed up as I was a bit tired investigating matter on Seagulls, I also had to deal with some dents on my FV, a cracked cylinder on a silver century etc etc etc
Well I also didn't know how to locate TDC.

But... you know, the bug get angry.

So let me tell you what I did.

Pick a crankshaft, a screwdriver and some rope. Put the shaft on the spark plug hole and tight it so it couldn't move.
I mounted the screwdriver on the block, that's my reference point.
Turned the flywheel, piston hits the crankshaft (gentle).
I marked the flywheel towards the screwdriver.
Turned the flywheel the other way around, the piston got Bang on the crankshaft again and I marked the flywheel again towards the screwdriver.
Where's the TDC, in the center of the distance of those two marks (I hope, tell me if I am wrong).
I marked the flywheel again towards the flywheel when the points start to open.
I did that two times. I had set the gap to 6 thou as my FVP didn't work nice in any other greater points gap.
Then I set the gap to 20 thou and marked again the flywheel. The angles (TDC,center of crankshaft, where the points open) that I measure with the help of fishing lines were

6 thou...... 35degrees
20 thou...... 48degrees



What's going on guys? Did I make a mistake? I was also thinking that the mixture wouldn't be compressed properly on around 50degrees.

I'm with H-A and Stelios keep it simple..

I would find TDC and mark flywheel and lower plate, then also mark the lower plate at 10, 20, 30, 40, 50 degrees before TDC. Then see when the points are first opening and check the marks. That will be close enough!

Oyster,

I agree completely with you. Thats the low tech method I described in my last post. It produces a quite adequate degree of accuracy for the purpose in mind. Its how I first came across the large (50 degree) advance. I thought then that I had better check it out dynamically, just in case something funny was going on.
Jeremy

Stelious what's the distance between the 6 thou & the 20 thou marks around the circumference, 1.47mm = 1degree, & the 6 degree to TDC.

I had no idea, increasing the points gap changed the timing so much.

Morning guys,

It's 17.5mm Charles. If I divide it by 1.47mm that makes 11.9degrees. (17.5mm is not a straight distance, it's the length of an arc. I use a flexible measuring tape.)
The protractor gives 48 minus 35, that's 13degrees. Very close, I was guessing that my results had an accuracy of +/-3 degrees. I think that verifies that my calculation may has a better accuracy, maybe a bit less than +/- 2 degrees.

Time to start searching for a book to read

Looks like I owe you an apology Jeremy, it certainly looks like the timing was set somewhere close to 50 degrees BTDC rather than in the early 20's like all the other Seagull models that have been measured.

After a great deal of searching I can find no other short stroke, slow running 2-stroke motor with such a large amount of advance.

Wrong again!

This is all fascinating, and if it were not for the females of the family getting ready for an assault on the Soth of France tomorrow I would be joining in the "crocodile clip 'n bulb 'n battery brigade.

I have no idea where the 23 1/2 degree figure came from, apart from British Seagull's own literature, and even that was not specific to the FV range. But 50 degrees does sound a lot.

Charles uk wrote:Stelious what's the distance between the 6 thou & the 20 thou marks around the circumference, 1.47mm = 1degree, & the 6 degree to TDC.

I had no idea, increasing the points gap changed the timing so much.

OK I forgot to measure the other distance 6 thou mark to TDC mark. This is 53.0mm. Divided by 1.47mm makes 36.1 degrees where I had measured with the protractor 35 degrees!



OK a revision of all of my results.

6 thou to 20 thou mark on the circumference is 17.5mm divided by 1.47mm makes 11.9deg, results from protractor is 13deg. Difference between calculations is 1.1deg.

6 thou to TDC mark on the circumference is 53.0mm divided by 1.47mm makes 36.1deg, result from protractor is 35deg. Difference between calculations is 0.9deg.

from all this, its quite surprising just how much of a difference 10 thou on the points can make!

way too early in my opinion to start the ignition cycle, but there you go!

seagulls, a strange breed indeed.
its any wonder they manage to run at all

has anyone looked REALLY closely at a piston crown when they've rebuilt an engine! full of pock marks like its been shot with a shotgun!
is this a timing issue or a compression issue or a fuel issue or a combination of all three!

jon

Just got back from a few days boating and glad to hear that 50 degrees advance (approx) is now accepted (am I right in this?) as the factory setting for FV/FVPs. Does this also apply to the LS?
Thanks for your apology Charles, but there was really no need.
I am glad that we are slowly learning more and more about these early little motors. I know that I am biased, but they really are the best!

I took FV2821 and FV6353 to use on my 10’ tender. Both performed admirably, with characteristics which were very different from running in a small tank at home. Some ad hoc adjustments of ignition timing were carried out, but I need to think about the results. Although starting, even when deeply immersed was very satisfactory. One curious aspect was the plug colour. After one run with FV2821, I looked at the plug and found that the electrodes were an olive green colour! Not grey, white or black but green! This was the same colour as the petroil mix, which was based on Shell Nautilius TC-W3 Outboard Oil. I was very surprised.
Anyway, the FVs pushed my dinghy along very nicely. If anybody knows the Yealm in Devon and the Ship Inn in Noss Mayo, they will find a very nice SJP inside near the main bar. The gents loo has been decorated with Seagull period advertisements, from, I guess the 1950s. The landlord also has a Seagull clock in his garage.

Back to ignition timing. Do the early 40 Minus and Forty Plus ie SJM/SJP have the same or different advance to the FV/FVP? I believe Jon, has some relevant measurement results.

Bruce, glad you like this topic. I look forward to your test results.
Also test results from anybody else who is interested in this topic.

Jeremy