Alan F.
Veteran Member
I've read some threads on the old HT site about overboring the SOHC 450 and how overbore pistons and rings are NLA from Honda. This got me thinking about how big you could safely go with a 450.
I'd like to do this with stock parts from another bike, young enough to ensure availability into the future.
Another key point would be to keep the necessary machine work to a minimum.
After looking around at lots of parts online I settled on a set of pistons with rings and cylinder jugs from ebay, in good shape for about $150 shipped. They're all from the same 13k mi. bike, a 2002 Triumph Bonneville T100 790cc.
Somewhere I downloaded a full size printable base gasket from a 450 (can't find it now) at each cylinder there is one stud nearer to the cylinder sleeve than the other 3:
It seems the jugs can be resleeved larger but this stud will be the limiting factor.
I measured 5mm between that stud and cylinder sleeve holes in the base gasket. The cylinder sleeve hole measures 83.5mm
So 83.5mm with 5mm on each side = 93.37mm
Which will be the largest sleeve OD that the block will accept.
In one of the threads I read TOOLS1 say that a .100" cylinder wall (2.54mm) will be a good minimum.
93.37mm - 5.08mm = 88.29mm as our max bore.
So if I found an 88mm piston, with an 18mm wrist pin, with pin to piston top distance same as stock....
It'd fit easily.
The T100 piston bore is 86mm, wrist pins are 19mm
(I'm hoping the SOHC 450 rods can be reamed from 18 to 19mm)
The Triumph sleeves measure 96.16mm OD.
I don't know if sleeve OD can be turned down or not, but I've got the idea of boring the block to accept these sleeves and grooving the sleeve with a ball endmill 4.5mm deep to clear the stud bore.
96.16 - 4.5 = 91.66
Sleeve ID is already 86mm, 91.66 - 86 = 5.66mm
5.66mm divided by 2 gives us a cylinder wall of 2.83mm or .1114" plenty according to what TOOLS1 had said in an earlier thread.
These pistons use a 19mm wrist pin, I'd read Longdistancerider mention that the 400 uses 17mm wrist pins but the 450 uses an 18mm wrist pin.
Can these rods be reamed from 18 to 19mm?
And piston pin to piston top measurement would need to be close to stock, an exhaust valve relief in the piston top may need to be added.
The bottom of the Triumph sleeves will need to be altered to a shape closer to stock, and the top engine case will need modification to fit the fatter sleeves also.
I'm not sure what can be done for a head gasket, make a copper gasket I suppose.
Will the difference between combustion chamber diameters and cylinder bores be a factor? Will the chambers need alteration?
I think the head will flow well but I'm not so sure of a stock exhaust.
Carburetors will require larger jets, I'd have to look at the carbs the Triumph uses
Thoughts?
I'd like to do this with stock parts from another bike, young enough to ensure availability into the future.
Another key point would be to keep the necessary machine work to a minimum.
After looking around at lots of parts online I settled on a set of pistons with rings and cylinder jugs from ebay, in good shape for about $150 shipped. They're all from the same 13k mi. bike, a 2002 Triumph Bonneville T100 790cc.
Somewhere I downloaded a full size printable base gasket from a 450 (can't find it now) at each cylinder there is one stud nearer to the cylinder sleeve than the other 3:
It seems the jugs can be resleeved larger but this stud will be the limiting factor.
I measured 5mm between that stud and cylinder sleeve holes in the base gasket. The cylinder sleeve hole measures 83.5mm
So 83.5mm with 5mm on each side = 93.37mm
Which will be the largest sleeve OD that the block will accept.
In one of the threads I read TOOLS1 say that a .100" cylinder wall (2.54mm) will be a good minimum.
93.37mm - 5.08mm = 88.29mm as our max bore.
So if I found an 88mm piston, with an 18mm wrist pin, with pin to piston top distance same as stock....
It'd fit easily.
The T100 piston bore is 86mm, wrist pins are 19mm
(I'm hoping the SOHC 450 rods can be reamed from 18 to 19mm)
The Triumph sleeves measure 96.16mm OD.
I don't know if sleeve OD can be turned down or not, but I've got the idea of boring the block to accept these sleeves and grooving the sleeve with a ball endmill 4.5mm deep to clear the stud bore.
96.16 - 4.5 = 91.66
Sleeve ID is already 86mm, 91.66 - 86 = 5.66mm
5.66mm divided by 2 gives us a cylinder wall of 2.83mm or .1114" plenty according to what TOOLS1 had said in an earlier thread.
These pistons use a 19mm wrist pin, I'd read Longdistancerider mention that the 400 uses 17mm wrist pins but the 450 uses an 18mm wrist pin.
Can these rods be reamed from 18 to 19mm?
And piston pin to piston top measurement would need to be close to stock, an exhaust valve relief in the piston top may need to be added.
The bottom of the Triumph sleeves will need to be altered to a shape closer to stock, and the top engine case will need modification to fit the fatter sleeves also.
I'm not sure what can be done for a head gasket, make a copper gasket I suppose.
Will the difference between combustion chamber diameters and cylinder bores be a factor? Will the chambers need alteration?
I think the head will flow well but I'm not so sure of a stock exhaust.
Carburetors will require larger jets, I'd have to look at the carbs the Triumph uses
Thoughts?