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Meriden Thruxton 650 engine spec #381074
06/27/11 6:56 am
06/27/11 6:56 am
Joined: Aug 2001
Posts: 1,081
Cheshire UK
Phatt Bob Offline OP
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Phatt Bob  Offline OP
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Joined: Aug 2001
Posts: 1,081
Cheshire UK
Hi all,
Does anyone have access to the engine spec for any of the factory Thruxtons made in the 60's. Info seems to be vague from the usual sources. I don't suppose there are any big secrets we haven't stumbled across already, but it would be nice to see them all in one place.

Looking for things like compression ratio, ignition timing etc. Service sheet 310 is OK so far as it goes for cams and followers etc but were any others fitted? Also to what extent was any lightening work carried out on the top and bottom ends? I once one had a "Thuxton" crank with a very narrow flywheel.

Any advice gratefully recieved.

Thanks and regards

Bob


Phatt Bob
'95 Daytona 1200
'98 Daytona 1200 dragbike
ex-850 T140 Caff Racer, 850 Triton, Morgo T120, Starfire and Pretend Daytona 500 owner
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Re: Meriden Thruxton 650 engine spec [Re: Phatt Bob] #381076
06/27/11 8:03 am
06/27/11 8:03 am
Joined: Jul 2005
Posts: 604
back down the 'smoke',England
6T Offline
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6T  Offline
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Posts: 604
back down the 'smoke',England
..can't help much regarding internals,mines only done 500(none racing)miles but its got the morgo 750 kit & quaiffe 5 speed box..here's some photo's.Notice the pushrods that had not seated properly in the standard rockerboxes,more on that later(another thread)Cheers...

Last edited by 6T; 06/27/11 8:05 am.

...I do not and cannot accept the principal that incompetence justifies dismissal...
BMW R1100rt
6T 1965
T110 1958
Re: Meriden Thruxton 650 engine spec [Re: Phatt Bob] #381082
06/27/11 9:58 am
06/27/11 9:58 am
Joined: May 2006
Posts: 509
melbourne, australia
7
76degree-triumph Offline
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76degree-triumph  Offline
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7
Joined: May 2006
Posts: 509
melbourne, australia
Gday Bob, years ago I bought a genuine Boyer race engine. Its fitted with the 3" radius followers but what was not mentioned in his book was the tube connecting the inlet followers to the exh to feed oil to the inlet side.



As I understand it the thruxton cams were part #E4220. These were also listed as T-Bird cams in 1961 or 62 for a short time. Ive got a set here but they have worn the nose off them.

This engine came with the "spitfire" cams, as per the Boyer book, not the 4220's.

Cam timing was IO 51 IC 72. EO 83 EC 47. All @.020".

I dropped those cams into my T140 road bike, it transformed it.

I have a 4220 cam on the inlet of my dirtbike but I cant find the timing events. It uses 'R' followers.
If you are interested I will try and dig them up.


1950 Speed Twin outfit
1951 Thunderbird outfit (76 degree racebike, or is it 90 deg now?)
1955 BSA D3 minibike outfit
Triumph solo's
Re: Meriden Thruxton 650 engine spec [Re: 76degree-triumph] #381088
06/27/11 10:39 am
06/27/11 10:39 am
Joined: Aug 2001
Posts: 1,081
Cheshire UK
Phatt Bob Offline OP
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Phatt Bob  Offline OP
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Joined: Aug 2001
Posts: 1,081
Cheshire UK
Thanks 6T and 76degree-triumph, this is exactly the sort of info I'm looking for.

6T, those look like mushroom headed tappets. Do you know if they were an original fitment or aftermarket? Also polished and shimmed rockers as I would have expected.

76DT, I once owned a set of thruxton tappet blocks in alloy bronze IIRC, they were bigger and slot machined for the 3" tappets was wider in the front to back dimension, it's hard to tell from the photo, but are the tappets longer than the 3059s? Also are they dome headed or cupped at the other end. I was told that if you used the shorter 3059s with 4220s the leading edge would dig in. Never actually got chance to try it. I've got a 4220 also, but assumed if the block needed machining to fit a bigger guide block, T140 inlets would have been simpler.

Thanks again all.

Regards

Bob


Phatt Bob
'95 Daytona 1200
'98 Daytona 1200 dragbike
ex-850 T140 Caff Racer, 850 Triton, Morgo T120, Starfire and Pretend Daytona 500 owner
Re: Meriden Thruxton 650 engine spec [Re: 76degree-triumph] #381089
06/27/11 10:42 am
06/27/11 10:42 am
Joined: Jul 2005
Posts: 604
back down the 'smoke',England
6T Offline
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6T  Offline
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Joined: Jul 2005
Posts: 604
back down the 'smoke',England
...I see Morgo do the Thruxton tappet blocks but the barrels have to be machined!
http://www.morgo.co.uk/tappet.html


...I do not and cannot accept the principal that incompetence justifies dismissal...
BMW R1100rt
6T 1965
T110 1958
Re: Meriden Thruxton 650 engine spec [Re: Phatt Bob] #381090
06/27/11 10:46 am
06/27/11 10:46 am
Joined: Jul 2005
Posts: 604
back down the 'smoke',England
6T Offline
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6T  Offline
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back down the 'smoke',England
..I don't have special pushrods in mine but THINK the Thruston used triunph 250 ones moded?Have you got the Stan Shenton book?Cheers..


...I do not and cannot accept the principal that incompetence justifies dismissal...
BMW R1100rt
6T 1965
T110 1958
Re: Meriden Thruxton 650 engine spec [Re: 6T] #381103
06/27/11 12:20 pm
06/27/11 12:20 pm
Joined: Aug 2001
Posts: 1,081
Cheshire UK
Phatt Bob Offline OP
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Phatt Bob  Offline OP
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Joined: Aug 2001
Posts: 1,081
Cheshire UK
Hi mate, yes, I have got it, but until you mentioned I'd forgotten...its me age.

It shows the flywheel and tappets etc quite nicely, but I reckon both the cams it shows are the same profile......

The reason I ask this is that I have an acquaintance who has a "Thruxton Spec" 69 Bonneville. I'm beginning to wonder if "Thruxton Spec" is a bit variable apart from all cosmetic bits!

Cheers

Bob


Phatt Bob
'95 Daytona 1200
'98 Daytona 1200 dragbike
ex-850 T140 Caff Racer, 850 Triton, Morgo T120, Starfire and Pretend Daytona 500 owner
Re: Meriden Thruxton 650 engine spec [Re: Phatt Bob] #381130
06/27/11 2:10 pm
06/27/11 2:10 pm
Joined: Jul 2005
Posts: 604
back down the 'smoke',England
6T Offline
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6T  Offline
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Posts: 604
back down the 'smoke',England
..I remember the quip quite well.. Stan Shenton told his employees.. "The Thruxton Bonnevilles arrived!!" to which someone said "but its not a works Thruxton is it!".....


...I do not and cannot accept the principal that incompetence justifies dismissal...
BMW R1100rt
6T 1965
T110 1958
Re: Meriden Thruxton 650 engine spec [Re: Phatt Bob] #381303
06/28/11 9:01 am
06/28/11 9:01 am
Joined: Jan 2007
Posts: 209
New Zealand
T
Trevor Stapp Offline
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Trevor Stapp  Offline
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T
Joined: Jan 2007
Posts: 209
New Zealand
Bob,

Check out http://www.hoppybikes.co.uk/
Talk to George Hopwood, great guy and wealth of infor.
Spannered back in teh 60's on Thruxtons.

Cheers,
Trev


66T100SR Cafe racer
59 T20 Cub
1938 - 53 5T Bitsa project, now a roller
Duplex frame under the bench
Re: Meriden Thruxton 650 engine spec [Re: Phatt Bob] #381308
06/28/11 10:29 am
06/28/11 10:29 am
Joined: May 2006
Posts: 509
melbourne, australia
7
76degree-triumph Offline
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7
Joined: May 2006
Posts: 509
melbourne, australia
Bob, Ive used the 4220 on the inlet for many years with 'R' followers with no probs or abnormal wear whatsoever. They are in a unit engine with a T140 topend and norton crank and rods.
STD T140 guide blocks.
The thruxton followers in the front to back dimension are around 1/8th longer then std or 'R'. They are in my 650 race engine at the moment so I cant measure them.
They are dome headed and although I have not measured the length the pushrods appear to be STD 650 items.
I hope this helps,
Chris.


1950 Speed Twin outfit
1951 Thunderbird outfit (76 degree racebike, or is it 90 deg now?)
1955 BSA D3 minibike outfit
Triumph solo's
Re: Meriden Thruxton 650 engine spec [Re: 76degree-triumph] #381487
06/29/11 7:13 am
06/29/11 7:13 am
Joined: Aug 2001
Posts: 1,081
Cheshire UK
Phatt Bob Offline OP
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Phatt Bob  Offline OP
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Joined: Aug 2001
Posts: 1,081
Cheshire UK
Thanks again folks,

Grumpy Trevor,
Funnily enough, this IS one of George Hopwoods motors, with the 3" followers and Spitfire (E6897 and 8 or his version) cams not E4220s, but sold to my mate as a Thruxton spec motor. Hence my question about what the spec was. Cam timings are similar for inlet but not exhaust, so they're obviously different beasts.

When is a Thruxton not a Thruxton? Does it need to have Thruxton cams to be a Thruxton, or just the word from an authoratative figure (e.g. Hoppy) that it can be considered a Thruxton.
I'm beginning to suspect the answer......

Bob


Phatt Bob
'95 Daytona 1200
'98 Daytona 1200 dragbike
ex-850 T140 Caff Racer, 850 Triton, Morgo T120, Starfire and Pretend Daytona 500 owner
Re: Meriden Thruxton 650 engine spec [Re: Phatt Bob] #404526
11/19/11 9:38 am
11/19/11 9:38 am
Joined: Nov 2011
Posts: 4
uk
S
Steve69 Offline
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Steve69  Offline
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S
Joined: Nov 2011
Posts: 4
uk
I tahe a copy of the alternative parts list for the 1964 thruxtons
if anyone is interested I could scan it. I have nothing for the
later thruxtons though I'am afraid.

-Steve

Re: Meriden Thruxton 650 engine spec [Re: Phatt Bob] #404595
11/19/11 7:54 pm
11/19/11 7:54 pm
Joined: Jun 2007
Posts: 5,848
Maui Hawaii
HawaiianTiger Offline

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HawaiianTiger  Offline

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Joined: Jun 2007
Posts: 5,848
Maui Hawaii
When I was restoring my '62 6T I hunted the world wide for E4220/1 cams and came up short. No wonder. Only later did I discover that these cams were the same cams used in the Thruxton. They must be coveted by collectors and classic racers. I ended up installing T110 cams and was never satisfied.
E4220 cams are ramped cams and I'm sure by then folks were discovering that the ramps were easier on valve train components. I have saved my cams even though they were not usable in my engine having rusted too much. I would like to have them duplicated and use them in a street rod.
Bill

Last edited by HawaiianTiger; 11/19/11 7:54 pm.

Bikes
1974 Commando
1985 Honda Nighthawk 650
1957 Thunderbird/T110 "Flying Tiger"
Antique Fans: Loads of Emersons (Two six wingers) plus gyros and orbiters.
Re: Meriden Thruxton 650 engine spec [Re: Phatt Bob] #404673
11/20/11 10:33 am
11/20/11 10:33 am
Joined: Jul 2005
Posts: 604
back down the 'smoke',England
6T Offline
BritBike Forum member
6T  Offline
BritBike Forum member
Joined: Jul 2005
Posts: 604
back down the 'smoke',England
Hi Bill,look up "David Newman camshafts" of Orpington,Kent... He's refaced cam followers for me,very good service and reasonable price... It wouldn't be too expensive to ship your cams,would it? Cheers!


...I do not and cannot accept the principal that incompetence justifies dismissal...
BMW R1100rt
6T 1965
T110 1958

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