OzVMX Forum
Marque Remarks => Spaniards (Bultaco, Ossa, Montesa etc) => Topic started by: VR250 on December 03, 2011, 08:33:55 pm
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Has anyone heard if its possible to modify a vr250 engine into an open class (300cc +) motor using pre 1975 sleeves pistons etc?
Got a spare motor lying around and curious if it can be done.
Im sick of running a 250 against open class bikes and need a little boost to help carry my ever increasing waistline over the finish line.
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The only thing I know of was a GP 360 motor in a VR running chassis
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Next to impossible to do with the existing VR cases (34M cases) An extreme overbore on the
VR cylinder, still does not give you an over 300cc displacement. Stud placement of the VR cases
makes the use of the 360GP cylinder a no go. Montesa just did not offer any pre 75' big bore motors
except for the 360GP engine, which can be swapped in easily, but is not a suitable option for what
you have in mind. As a side note, the 77' VB 250 can use a Cota 348 piston which will yield a 305cc
displacement.
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This is the VR360 (VR 250 frame with a GP 360 engine) built by Lyall O'Brien that his son Gary won the 1973 Grand National on. I will restore it next year hopefully in time for CD9.
Stan.
(http://i991.photobucket.com/albums/af39/gf079/CD8%20pics/SAM_0877-1.jpg)
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(http://i914.photobucket.com/albums/ac346/albrid-3/GaryOBrienGrandNationalChristmasHills1973Montesa360GP.jpg)
Gary O`brien on the Montesa 360GP VR 1973 winning the Grand National.
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....are they the same bike??
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Yup! ;)
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Sorry for the poor quality of the picture. Lyall sent me this pic of the VR 360 some years ago.
Of note is the sprocket cover.
(http://www.southwestmontesa.com/360vr.jpg)
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He must have been worried about throwing the chain with the LTR. Is there a fair gap between the swingarm pivot and countershaft?
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Yes, there was a long distance between the sprocket and the swingarm pivot.
Was alway's a problem with Montesa motors. A byproduct of using a dated engine
design well in to the eighties.
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Sorry there are 2 different bikes there.
The one of Gary racing is an early Vr.
The 2 others are late Vr's.
So someone out there has an early Vr with a 360 motor hiding in their shed somewhere in oz!
Come out, come out, wherever you are.
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They could be the same bike only with the addition of lay down shock mounts and other minor changes.
The bike appears to have been "enduroized" in it's last incarnation.
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the other vr 360 still lives with its owner and its not me and he doesnt want to sell it thats all i can tell you cheers
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Sorry there are 2 different bikes there.
The one of Gary racing is an early Vr.
The 2 others are late Vr's.
So someone out there has an early Vr with a 360 motor hiding in their shed somewhere in oz!
Come out, come out, wherever you are.
VR250, the three photo's are the same bike which I have in the shed. In 1974 Lyall up dated Gary's 73 bike with a 74 tank seat and wheels. In late 74 the rear suspension was modified. The bike was sold later through Ryan's in NSW to the guy that is pictured in my photo. He then modified it to race enduro's and that is the state that I bought it in.
I have spoken to Gary O'Brien recently and he confirmed the history as he remembers it. When I get around to it I intend putting it back to the same as it was when Gary won the 73 Grand National on it. I hope one day to intice Gary into doing some laps on it at an Demo event somewhere, but that's sometime down the track.
Stan.
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stan your right but there still live one more that was built by lyle
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stan your right but there still live one more that was built by lyle
Chis, I didn't know that still existed. I would be very interested in hearing about it's known history. The one I have came with some paperwork from Lyall and some specially made conrods that were manufactured for Gary's bikes. I ate plenty of dirt from behind these bikes in 73 and 74 before Gary received a prototype VA360 for the 75 season. Got to eat plenty from behind that one as well :D. I would love to know where that prototype ended up.
Stan.
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Lyle sent me some info/pics on this bike too, which I've previously posted on here. I'll have to check my info but I'm sure he said he built about 4 VR360's. Of course he could have been stretching the truth (which wasn't unheard of!)
Did Ed Lancaster ride one too?
He also built some 360 63Ms too but he said they weren't so successful. I know Ed rode 1 of those. Just as an aside, how many remember Ed won an Oz title on the humble 4sp 125 Mont in 72 or 73
Getting back to the original question about the VR engine, I'm no Montesa engine building guru, but the VR/V75 sleeve is quite thick - OD is 80.5mm w 70mm bore. I'd have tho't that could be safely bored to take a 75mm piston, perhaps even 76mm, if you could find one w a 16mm gudgeon to suit the rod.
Perhaps try watercraft pistons. Kaw often used 16mm gudgeons.
That would give about 280 - 290cc. But I have no idea if the stock rod/big-end could handle it reliably.
It would take some boring tho. The liner is very hard. Lyle once told me the Rockwell hardness but I've long since forgotten it.
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how many remember Ed won an Oz title on the humble 4sp 125 Mont in 72 or 73
1972
1: Ed Lancaster......Montesa
2: Steven Cramer...KTM
2: Geoff Taylor......Yamaha
Cramers second spot is the earliest title rostrum appearance by KTM too.
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Gary was the only person racing the VR360, the 73 bike was change due to an accident at Calder Rally cross, Gary`s front wheel hit a bog hole which was on the corner of the S-bend and shot gary and the vr off the track over the bitumen track hit the guard rail and rolled on top off the guard rail and came to rest, I was racing that same day same class because I hit the same hole on my husky and it to shot the rear wheel up in the air and rode the full length of the back straight on the front wheel. Gary`s Monty was wrecked Tank, frame etc. then Lyall built the 74 model.