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 Post subject: Re: 1990 750 Sport for sale
PostPosted: Fri May 25, 2018 11:23 pm 
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Joined: Tue Mar 13, 2012 9:02 am
Posts: 319
Location: The Blue Mountains, NSW, Australia
model: other
year: 1988
Great stuff Challenger392 sounds and reads like your getting fairly close to the cosmetic stage of the revival.

Cheers

Peter

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 Post subject: Re: 1990 750 Sport for sale
PostPosted: Sat May 26, 2018 11:41 am 
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Joined: Sun Mar 25, 2018 6:39 pm
Posts: 36
Location: Vermont,USA
model: 750 Sport
year: 1990
Yes, the cosmetics will probably take a back seat to some other projects for the summer. Ill just ride the bike naked for now to work out any more mechanical problems. Then make her real pretty this coming winter. On another note. What do y'all recommend for motor oil? Is synthetic a good or bad idea?


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 Post subject: Re: 1990 750 Sport for sale
PostPosted: Wed Jun 13, 2018 9:26 pm 
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Joined: Sun Mar 25, 2018 6:39 pm
Posts: 36
Location: Vermont,USA
model: 750 Sport
year: 1990
Update, for all the fans that are watching :D I changed the oil, and took her for a ride. Rode 25 miles with no problems, still on the old tires. The bike ran great!!! Makes pretty good power. It seems to like the long intake runners in the mid range. Once I got it back I decided to install the new timing belts I purchased. After I got everything back together I tried to start it and it sounds HORRIBLE. Some disassembly revealed I bent a valve. Im sad, I broke my favorite toy. Im not sure what went wrong. I double, triple, guadruple checked the timing before I attempted a start it. How hard can it be, you line up the timing marks on the pulleys with the marks on the case/heads. Any advise would be appreciated.


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 Post subject: Re: 1990 750 Sport for sale
PostPosted: Thu Jun 14, 2018 9:58 am 
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Joined: Thu Nov 29, 2007 2:38 am
Posts: 283
Location: UK
model: 907 I.E.
year: 1990
Challenger392 wrote:
Update, for all the fans that are watching :D I changed the oil, and took her for a ride. Rode 25 miles with no problems, still on the old tires. The bike ran great!!! Makes pretty good power. It seems to like the long intake runners in the mid range. Once I got it back I decided to install the new timing belts I purchased. After I got everything back together I tried to start it and it sounds HORRIBLE. Some disassembly revealed I bent a valve. Im sad, I broke my favorite toy. Im not sure what went wrong. I double, triple, guadruple checked the timing before I attempted a start it. How hard can it be, you line up the timing marks on the pulleys with the marks on the case/heads. Any advise would be appreciated.


That is really sad news, the reason it happened is because either the markings were wrong or you did not alligned them correctly.

Another possible reason is that you did not give the right tension to the belts and it "jumped" the pulley.

I never trust markings so I always make my markings before taking off the belts.

Moreover you need to be very careful with the fitting as one of the cams is always under pressure from the closing springs and tend to slip backwards (usually the vertical Cylinder)

One rule is to remove the sparkplugs , replace the belts, tension, then do several turns of the crank by hand (4-5th gear and turn slowly the back wheel) just to check if there is any binding which means you have a valve touching a piston and that something is wrong.

The best would be fitting a comparator in place of the spark on the vertical cylinder, so you know exactly where the piston is when you turn , this way it helps to understand the "whole picture" and potentially avoid any damage.

Now you need to check if the problem is for one or both heads, hoping the damage is only to the valve and not to the head or the piston.

I would source a set of heads , get them ready on the bench (tollerances, etc) and just swap them over...


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 Post subject: Re: 1990 750 Sport for sale
PostPosted: Fri Jun 15, 2018 8:26 pm 
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Joined: Sun Mar 25, 2018 6:39 pm
Posts: 36
Location: Vermont,USA
model: 750 Sport
year: 1990
Is it possible that someone before me could have reassembled the bike wrong after a valve service? Resulting in the timing marks not lining up correctly. (trying to avoid personal blame)


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 Post subject: Re: 1990 750 Sport for sale
PostPosted: Fri Jun 15, 2018 8:47 pm 
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Joined: Thu Nov 29, 2007 2:38 am
Posts: 283
Location: UK
model: 907 I.E.
year: 1990
the pulleys are all fitted with keys , the only way to get a pulley "wrong" is to remove it and refit it without a hey, this way you don't really know how the camshaft is aligned and you could get it completely out of sync

did you remove the pulley and forgot top refit the key?

As mentioned before when all the markings are aligned , one of the camshafts remains in tension (on my 907 it was the vertical) so it tends to turn backwards when you remove the belt (or the pulley).

if by any chance the pulley was removed and no key was fitted then most likely there will be mis-alignement.

Another thing is if you my any chance rotated the engine, and did not check the alignment of the lower pulley, the one on the cranckcase.

one piece of advise is always to mark the position of the 3 pulleys with a marker/ dot of paint so you can immediately recognize and NOT make mistakes and it is much easy not to get confused... sometimes we rely on markings that we thing are correct then we realized, too late, that we picked the wrong ones.


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 Post subject: Re: 1990 750 Sport for sale
PostPosted: Sat Jun 16, 2018 11:17 am 
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Joined: Sun Mar 25, 2018 6:39 pm
Posts: 36
Location: Vermont,USA
model: 750 Sport
year: 1990
Someone on another Forum has a set of 900ss heads they say should fit. Does that sound right? He says they are "Big Valve" heads.


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 Post subject: Re: 1990 750 Sport for sale
PostPosted: Sat Jun 16, 2018 12:41 pm 
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paso grand pooh-bah

Joined: Thu Jun 21, 2007 12:00 am
Posts: 1443
Location: Gothenburg, SWEDEN
model: 907 I.E.
year: 1991
Big valve heads are marked V2, small valve W.

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907 I.E. -91
M900 -97
MTS 1100s -07


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 Post subject: Re: 1990 750 Sport for sale
PostPosted: Sat Jun 16, 2018 1:43 pm 
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Joined: Sun Mar 25, 2018 6:39 pm
Posts: 36
Location: Vermont,USA
model: 750 Sport
year: 1990
Yes he said they are marked V2, are V2 and W heads interchangeable?


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 Post subject: Re: 1990 750 Sport for sale
PostPosted: Sat Jun 16, 2018 5:30 pm 
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paso grand pooh-bah

Joined: Thu Jun 21, 2007 12:00 am
Posts: 1443
Location: Gothenburg, SWEDEN
model: 907 I.E.
year: 1991
Yes.

Edit: V2 and W heads for 904 cc are interchangeable.

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907 I.E. -91
M900 -97
MTS 1100s -07


Last edited by Tamburinifan on Sun Jun 17, 2018 2:38 pm, edited 1 time in total.

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 Post subject: Re: 1990 750 Sport for sale
PostPosted: Sat Jun 16, 2018 6:01 pm 
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paso grand pooh-bah
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Joined: Sun Jul 18, 2004 12:00 am
Posts: 5236
Location: southern Germany
model: 750 Paso
year: 1987
No! But for another reason.
900SS heads won't fit on a 750 engine.


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 Post subject: Re: 1990 750 Sport for sale
PostPosted: Sat Jun 16, 2018 7:01 pm 
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Joined: Sun Mar 25, 2018 6:39 pm
Posts: 36
Location: Vermont,USA
model: 750 Sport
year: 1990
Bummer, I was all excited for the bigger valves/ cam.


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 Post subject: Re: 1990 750 Sport for sale
PostPosted: Sat Jun 16, 2018 7:48 pm 
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Joined: Thu Nov 29, 2007 2:38 am
Posts: 283
Location: UK
model: 907 I.E.
year: 1990
Most 750s have 41/35 some 900s have the same so you need to be careful anyways. Most 900s are 43/38 and the 100ds should be 45/41

I read that the 800ie had the 43/38s but I don't think it will fit the 750 heads most likely the 800 was a 900 downsized but would be interesting checking....

The 600 and 620 definetively will fit the 750 but valves are very small, 35/30

Keep looking on ebay they show up regularly, sport 750, ss 750 or paso any will do. The other thing is fixing what you have , maybe the damage is minimal and in the endo you might just be replacing a valve and making a "big service" .


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 Post subject: Re: 1990 750 Sport for sale
PostPosted: Sun Jun 17, 2018 9:24 am 
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paso grand pooh-bah
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Joined: Sun Jul 18, 2004 12:00 am
Posts: 5236
Location: southern Germany
model: 750 Paso
year: 1987
The 900 heads with the 750 valves were i.e. used in the Cagiva Elefant were they make sense considering it was a bike developed also for off-road use.

600 piston 80mm diam
750 piston 88mm diam
900 piston 92mm diam (larger cylinder stud distance than 600/750)

compression ratio
600SS 10.7:1
750SS 9:1
750 Sport 10:1
900SS 9.2:1

Considering that the cylinder head's combustion chamber diameter always matches the cylinder bore it should be clear why a 600 head can't be used on a 750 (valve size differences aside). Also since 600, 750 and 900SS pistons have a flat dome but the engines have different compression ratios it's obvious that the combustion chamber volumes are different. The 600SS head will have a volume of ca. 62ml to achieve 10.7:1. If that would be fitted on a 750SS the CR would jump from 9:1 to 13:1. Actual volumes may differ but this is just to get an idea.
The 900SS must have a combustion chamber volume of around 110ml to get a CR of 9.2:1. The same volume in a 750SS head would lower CR to 7.8:1. Maybe that would be acceptable when installing a turbo but on a normal aspirated engine larger valves and higher lift cams wouldn't make up for that power loss.

Not sure you really want bigger valves and higher lift cams unless you're always pushing the bike hard. It makes more sense to do one or the other depending on which result you're after and what else you're planning to do to the engine. I would consider just keeping the standard valves, installing cams from a carbed 900 (OHT/VHT) and advancing them a bit.


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 Post subject: Re: 1990 750 Sport for sale
PostPosted: Sun Jun 17, 2018 10:07 am 
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Joined: Thu Nov 29, 2007 2:38 am
Posts: 283
Location: UK
model: 907 I.E.
year: 1990
Nice post!

The only thing I would change is the advice on the cams, I personally would go for the ST2 version which is the preferred one for all raving BOT stuff . These have a higher lift and will need to be checked for piston clearance.

Having said that I would not bother in changing anything that engine is asmatic and whatever you do to it is not going to make it more powerful unless you spend a lot of money and time , I know it for experience. Much cheaper to get a 900 and do an engine swap...

Going back to the cam specs, Brad Black in Oz keeps a very interesting website full of info and hi has a specific page on camshafts

http://www.bikeboy.org/duccamspec.html

Well worth studying. He also has a lot of info on many other things as he likes to tinker on the dyno


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