Interchangeability thread

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rosbullterier
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Interchangeability thread

Post by rosbullterier » Wed Mar 12, 2008 1:04 am

Your advice is that the 170 and QB blocks are best left to their own crankcases than fit to Century cases. ( they don't fit?)

However, what is the bearing weakness in the 170 - is it weaker than the Century? I presume the QB crank and rod is different to the 170?

Its very difficult to compare anything with the QB, they are not so plentiful!

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charlesp
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Post by charlesp » Wed Mar 12, 2008 9:40 am

I see that you too are suffering from the 'double post' syndrome. At first I put it down to too much Ringwood Bitter.

I don't think the 170 is inherently weaker than the Century, the problems seemed to occur with roller bearings on later models.

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Post by charlesp » Wed Mar 12, 2008 11:33 am

Of course, I was wrong earlier.

The 170 has a plain aluminium big end cap, which doesn't last for ever, and there are apparently no more.

So if you have one, treat it gently

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Post by rosbullterier » Wed Mar 12, 2008 5:55 pm

Yes I spoke to John today who told me they have no shells and the crank runs straight in an aluminium cap! Also all Seagulls run straight in their bearing caps without separate shells, except he can only remember replacing two in twenty years - they are all bronze (phosphor bronze?)
Anyway, beside explaining my phobia for incorrect spelling is why I didn't edit my first thread in time to prevent duplication - important question to ask: ( I didn't dare ring John back yet again) is the 170 flywheel removed with a puller?
Thank you very much, and if my elderly machinist neighbour can successfully make a bearing cap copy in bronze I'll let you know ( we are just starting negotiations)

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Charles uk
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Post by Charles uk » Wed Mar 12, 2008 8:19 pm

Somewhere at home I have some Autocad drawings of the 170 endcap but they are only hard copies, as the computer they were on died when I get home I could talk to your machinest, To explain where I got to in this quest.
the major problem is you could make a batch, but the bolt holes are in different locations in every rod that I've seen, so every one has to be fitted by the machinist before the lower half of big end hole is bored.
It's sunny here in Kiwiland.

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40TPI
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Post by 40TPI » Wed Mar 12, 2008 10:41 pm

rosbullterier wrote:............ Also all Seagulls run straight in their bearing caps without separate shells, except he can only remember replacing two in twenty years - they are all bronze (phosphor bronze?).................

Maybe only half the story. The pics are both # S1294 102cc conrods (102, Century/Silver, 75, 80 & 90 models) showing ali alloy endcaps with p/bronze liner/shell. Not all p/bronze endcaps. The second picture shows a less healthy specimen where the liners have become detached and which gives a better idea of the individual components.

Image

Image

Peter

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Post by rosbullterier » Thu Mar 13, 2008 12:01 am

That looks very scary. I shall not run this 170 until I have a p bronze bearing cap. Thanks

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Post by Charles uk » Thu Mar 13, 2008 7:32 am

Many 170's have run for years without any problems.
By all means check the big end bearing condition, if it's tired fix it, if it's ok use it like it was intended, but don't over rev it out of gear,
& run it on 20 : 1.

I don't know if this will prevent problems, I use all my 25 : 1 Seagulls at 20 : 1 it makes me feel more confident.

Charles in NZ

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40TPI
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Post by 40TPI » Thu Mar 13, 2008 3:47 pm

The big end pictures above were not meant to alarm! simply to show that the main type of conrod endcap was neither wholly ali nor PB. I have no idea how the smashed conrod met its fate but the piston has a hole punched through the top so I'd guess it was a ham fisted attempt at a seize clearance. The motor arrived as a pile of bits in a cardboard box! The witness marks, similar to PEM/clench nut marks which are just visible on the inner surface of the end cap and conrod suggest that the PB linings were pressed into the end cap and con rod. Anybody know how this was doen on the line?


Peter

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charlesp
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Post by charlesp » Thu Mar 13, 2008 4:05 pm

Obviously my post suggesting it would be richer is completely bonkers - there's a lesson on rushing to post when you should really read the original properly. I've deleted it now!

Having seen the way many Seagull owners mix their fuel - by the 'that looks about right' method, then I'm sure that won't make much difference either way

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40TPI
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Post by 40TPI » Thu Mar 13, 2008 4:19 pm

Hilarious Charles!

Too many people posting and editing at once!

I notice Vic is online as well so I'd better check if he has put his tuppenorth in before I post this!

I posted on top only to wonder where your post had gone! So I deleted my arithmetic in my post above since it was hanging there without any logical precursor in the thread!

In fact the numbers are quite surprising (although predictable when you think of small percentage changes in small and large numbers) . The petrol reduction is 0.923% going from 25:1 to 20:1 whereas the oil increment is 23.8%

Peter

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charlesp
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Post by charlesp » Thu Mar 13, 2008 4:37 pm

You're right about the numbers. I have always found it a little odd that the mixing instruction changed so many times in the early days - in fact it makes you wonder about just how variable the various oils were.

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40TPI
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Post by 40TPI » Thu Mar 13, 2008 4:56 pm

Actually I looked down on the pad at the wrong number. Before anybody jumps it should be 0.9599%.

As you say many mix with abandon and the lubricating qualities of oils are not going to be identical. Makes you believe that these engines are either engineering miracles and very tolerant or nobody appreciates the amount of wear taking place since the hours run per engine per year is usually very small in terms of total engine life.

Now that we are back in sequential mode have you any guess on the manufacture of big ends as per my note above?

Peter

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charlesp
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Post by charlesp » Thu Mar 13, 2008 5:39 pm

Not so much a guess, more of an eyewitness report.

By this time British Seagull's sales of motors had really fallen away to four figures annually. The 170 was one of a number of manful attempts to modernise after a fortune had been spent on Conran Associates ( he of 'Habitat' fame) who told the directors that modernisation was the thing. This was the first of the completely new designs, and of course had the cowling that was intended to tell the world that British Seagull was 'modern'. The same message was conveyed by steel tanks, blue paint, a modern logo, and 25:1 mixtures in other parts of the range.

Conrods and endcaps for the 170 were all made up and machined by one man - Ken Rolfe - at the factory. This never really got into a 'production line' way of doing things because there were never very many 170s made.

They were made as a matched up set, and really one should attempt to find a conrod and cap together. They were drilled in a jig, of course, but British Seagull were never exactly High Tech.

Apparently Doug Hele - the Engineering Director at that time - wouldn't allow these motors to be favoured with the bronze shells they so obviously need.

British Seagull in it's later years did many strange things.

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40TPI
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Post by 40TPI » Thu Mar 13, 2008 7:10 pm

Actually it was the pressing of the bronze shells into the earlier ali end caps and con rods I was curious about. The "clench nut /PEM" witness marks look to have been formed by a pressing process.

Peter

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