Benelli 750 SEI

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Anonymous

I have just purchased an early 750 with a blown engine for a grand.
Who and where could rebuild this unusual motor, does anyone know?
The cosmetics aren't too hot either but it's complete and the basic structure is fine.
Ta.

kevash
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Re: Benelli 750 SEI

I believe the engine was very closely based on a Honda 500 Four of the same period, so it'll be worth asking a classic dealer who has experience in those. I gather many components are even interchangeable, although this is not definitive, it's only what I recall from (too) many years ago.

749R (not verified)
Re: Benelli 750 SEI

Thanks Kev, you are right, bore and stroke etc and valve sizes appear the same.

A really good and long 'Google' has thrown up 2 classic bike builders, although circa £1,600 for the motor alone is the best price for a total engine once over,
I am thinking maybe a grand or so for chrome, other cosmetics etc.
Some more for a few parts i need, like a new seat.

If i can get the thing done, looking good and running like new for £4,500 i will be happy.
It surely will fetch more at some stage as they get rarer?

silvercub
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Re: Benelli 750 SEI

You might be interested in this article.

http://data.sohc4.net/AR500/500bw.pdf

We are a broad church at ashonbikes (in the broader sense of church!).

kevash
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Re: Benelli 750 SEI

I'm not particularly in touch with classic values but £4500 for a rebuilt and well restored 750 Sei sounds like a bargain, and it's not going to depreciate either, assuming the condition stays good. What about the pipes an silencers? You'll be very lucky if those are in good nick, and if they're not I imagine a full set of six could easily add 50 per cent to your rebuild costs. Availability could be a problem too.

749R (not verified)
Re: Benelli 750 SEI

Yes, pipes were the single biggest reason the bike cost me £1,000 only, Kev. The downpipes were fine having been well greased and internally oiled prior to storage but the silencers, despite the grease and oil are being replaced. A friend who does custom pipes for a living is sorting me out a set of plain stock-looking silencers for £500 so not too tragic.

749R (not verified)
Re: Benelli 750 SEI

The owners club has since told me that £8000 is the going rate for a nice 750, so that's encouraging as the pounds go flying out of the wallet!

Silvercub-cheers. Interesting link, ta.

Navy Boy
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Re: Benelli 750 SEI

Show us a picture will ya!

I haven't seen one of these for years!

749R (not verified)
Re: Benelli 750 SEI

I will put some (restored) pics up.

749R (not verified)
Re: Benelli 750 SEI

Moved the 750 on!
OMG. The restoration was going to cost a mint and i wanted to do it properly.
Gawwwn but not forgotten!

kevash
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Re: Benelli 750 SEI

That's a shame, but probably wise...

749R (not verified)
Re: Benelli 750 SEI

Yes Kev.
Some bikes are almost always worth a punt on a restore, but with something like the 750 the market can be very unreliable.
I had a 1957 DBD34 Gold Star for a while (complete with RRT2 'box, Goldie silencer and GP carb.) and it was never going to lose me any money, for example.
I made plenty on it.
The Honda CBX 1000 MK1 is always worth money, also.
I had 3 of those and i still love them.

bakes
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Re: Benelli 750 SEI

Im am looking for another 750 anyone got one they want to get rid of
wish id known you where getting rid of yours 749R

749R (not verified)
Re: Benelli 750 SEI

Sorry about that. I got rid of it when i started adding up what it needed, to become mint.

pittsy
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Re: Benelli 750 SEI

I restored a Benelli 350 RS 4 cylinder back to mint in the late 80's. lovely little thing. Engine clearly based (read "copied") on a Honda 500 four.

I still have the owners handbook, mint condition, in Italian!

All the chassis parts for the smaller fours ie: forks, brakes, yokes etc are moto guzzi. Eg: V50 etc. Maybe the same goes for the SEI? This would help narrow your search considerably, as it did mine!

Good luck.

BiKenG
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Re: Benelli 750 SEI

Kev's right, the Benelli 750 Sei was basically a Honda CB500 four with an extra cylinder at each end. Truth is, Benelli even asked Honda for a bike so that they could copy it, but IIRC Honda declined.

pittsy
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Re: Benelli 750 SEI

Did the Honda 500 four have a primary hy vo chain tensioner, do you know?

BiKenG
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Re: Benelli 750 SEI

pittsy wrote:
Did the Honda 500 four have a primary hy vo chain tensioner, do you know?

Ah, you got me there. It's so long ago now, but I don't think it did. AFAICR all the SOHC engines used normal chain then introduced HyVo with the DOHC engines.

pittsy
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Re: Benelli 750 SEI

The benelli 654 I once stripped down had a morse chain primary drive without a tensioner.

I'm reasonably confident in saying the Honda cb750, 500, 400 etc sohc engines all had, what the press described as hy vo primary chains. Whether they were using hy vo as a generic term I'm not sure.

I think that the hy vo tooth form and morse tooth form look the same but are slightly different. The term hy vo seems to get used as a generic term for both. Unless it was morse who made the "hy vo" chain. Can't remember!

Morse themselves made a few different styles of "toothed" chain but I think only one was taken up by the automotive industry.

I seem to recall that the above bikes all used roller chain for the cam drive. It was the dohc Honda's which started the use of "hy vo" cam chains (certainly in honda's, if not the rest)

BiKenG
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Re: Benelli 750 SEI

In fact the SOHC CB750 used two roller chains for primary drive. Can't remember about the 500 and 400 though.

The Japanese referred to the Morse/HyVo style as "Silent type" chains. I don't know now if they really were Morse or HyVo or their own derivative of that idea although I almost certainly did at the time.

pittsy
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Re: Benelli 750 SEI

BIKenG

I must apologise. After a bit of searching I've found a (blurry) cutaway drg for the very first cb750k. It looks to have duplex roller chain as primary drive. (i did say "reaonanly" confident!).

One would assume it must have had a tensioner. Can't see.

None of this matters anymore but I like to know if I'm wrong. I'll try and check on the others if I get a mo. the Benelli range was modelled on the Honda 500 four so I'll see what I can find on that.

pittsy
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Re: Benelli 750 SEI

Had crossed posts then! By the time I'd written mine, you'd beaten me to it.

Being the saddo that I am, I kept a really old "motorcycle sport" magazine which really went to town on the toothed chain business. If I can find it I'll let you know.

pittsy
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Re: Benelli 750 SEI

Looking on cmsnl micro fische. Both the Honda cb400 and cb500 sohc fours had roller chain cam and toothed chain primary.

I wouldn't mind being clear in my own mind regarding the difference (if any) between morse and hy vo so I'll get back to you.

Initially I think testers used to refer to it as "morse type" and "silent chain". Then later the term hy vo seemed to be used.

pittsy
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Re: Benelli 750 SEI

The chain in question is classed as the INVERTED TOOTH chain. The same chain is also called the SILENT chain. There are American National Standards (ANSI) for it and it's chain wheels or sprockets.

One important characteristic of the inverted tooth chain is that as the chain pitch increases due to wear in the joints, the chain shifts outwards on the teeth of the wheel, engaging the wheel on a pitch circle of increasing diameter. The result of this is that the pitch of the wheel teeth increases at the same rate as the chain pitch.

Morse referred to theirs as hy vo, meaning high velocity (so morse and hy vo ARE one and the same).

Inverted tooth chains operate at substantially higher speeds than roller chains. They undergo hardly any "chordal fluctuation", which is a bad trait of roller chains. They are reckoned to not require tensioners.

I presume the tensioners on hy vo cam chain drives is due to the quite dramatic expansion of the cylinder and head. That and the need to maintain accuracy of timing. One thing for sure, if it didn't need a tensioner, they wouldn't put one there, on cost grounds and friction. Maybe Kevin can enlighten further.

BiKenG
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Re: Benelli 750 SEI

I think the CB750 twin chains had hydraulic tensioners. Whatever they used, it was bulletproof.

I never did any of the technical training on the SOHC fours as they were just before my time at HUK. But I do still know the person who did all that training for the dealers so I can ask him if we need to.

Ask me about the CBX1000. I did most of the training for that. Beautiful engine. So elegantly designed.

Tensioners are required for cam drives to keep the tension side of the chain, well, in tension, to keep the timing accurate. If the cam is flapping about (as it were) it doesn't do much for the cam timing and engine efficiency.

pittsy
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Re: Benelli 750 SEI

BIKenG

No need to trouble your friend, unless he wants in! That's great!

pittsy
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Re: Benelli 750 SEI

Chordal Effect (Chordal Action): The effect produced by the chain joint centers being forced to follow arcs instead of chords of the sprocket pitch circle.

Gekom57
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Re: Benelli 750 SEI

Hi,
My name is Jerzy and I also have become a new owner of Benelli 750 sei. So I think will have lots of common subject to write about as my bike needs some restoration work too.
I have already done my googling and I know that the parts are still quite easy to get
There is one place in Germany and one in Spain.There is good idea is to join a motorcycle club and get some parts from members who may have what you lookin for.
My Benelli 750 sei comes from the lats year production which is 1978 year.
Cheers Jerzy

roundincircles
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Re: Benelli 750 SEI

Gekom57 wrote:
Hi,
My name is Jerzy and I also have become a new owner of Benelli 750 sei. So I think will have lots of common subject to write about as my bike needs some restoration work too.
I have already done my googling and I know that the parts are still quite easy to get
There is one place in Germany and one in Spain.There is good idea is to join a motorcycle club and get some parts from members who may have what you lookin for.
My Benelli 750 sei comes from the lats year production which is 1978 year.
Cheers Jerzy

Jerzy, any photos? Great bike and engine.

Gekom57
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Re: Benelli 750 SEI

roundincircles wrote:

Hi,Jerzy, any photos? Great bike and engine.

I have just bough it on e-bay so the bike is steel in transit from Queensland to Sydney in NSW .It has 6 in 2 exhaust system, modified front including handlebar to be suitable for racing.There is only speedometer ,no tachometer. All that I intend to bring to a original condition.Nice blue color of fuel tank and side covers.There is some rust and corrosion to chromed and alloy parts, but that is normal when a bike is not in use for 10 or more years.Thanks God it was not kept in the open, I did this to my Kawasaki Z650SR and I felt sorry for it.
Cheers Jerzy

pittsy
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Re: Benelli 750 SEI

If memory serves, a lot of the "non engine" parts were common with guzzi's of the period. This may help with sourcing spares.

(A version of the smaller fours was cataloged by guzzi as well as benelli. I've never seen one in the flesh however!)

Hope you enjoy riding your project.