GP 150 to suit ts185 + std crank.

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gimme2
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Gday all ,this will be my first post.
I have dismembered an unfinished project a 1970 gp 150. all seems good other than a few missing bits and an 18mm carb . After removing the piston.. I guess I'm up for a rebore it measures 57.2 . Rings were stuck in their homes like crabs in rocks during a school excursion . One broke.
Seeing I need a rebore...
How much extra work do ya rekon it would be to fit a 185 piston?
Do I need to modify the piston / barrel ? the crank ? Port timings?
Have you done this with good results?
Cheers.



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Stokie
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You'll need to take the bore out to 64mm for the Suzuki TS185 piston
I'm not sure if a 150 cylinder will go that far - check the MB Tech site as I'm sure that'll tell you.
You'll either need to have the barrel shortened (topped & tailed) if using the standard crank and the standard 107 rod or you could use a crank with a TV rod or RD400 rod fitted and then adjust with a packing plate.
You'll want it porting too, oh and the head re-profiled to suit the piston.

These days with various small block kits available it's probably simpler and possibly more cost effective to buy something off the shelf .....
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Stokie
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Here you go ...
Credit to Mark Broadhurst of MB Scooters as copied from his incredible Tech Site
http://www.mbscooters.co.uk/info/cylind ... -x+42.html

150 / 175 – 190 Suzuki conversion

150 cylinders bored to 190cc or better still 175 cylinders bored to 190cc using a Japanese Suzuki piston starting at 64mm with a compression height of 32mm or use our own MB Race-Tour pistons at 64mm with a compression height of 30/31/32mm. 150 cylinders should not be bore straight out to 66mm (200cc) but 175 cylinders can be and have been ok in the past.

Use the original crankshaft (107mm) and ignition set up or convert to standard or race type GP crankshafts.

PROS: Excellent quality Suzuki piston kits either genuine or pattern and easily available with a good selection of oversizes 64 to 65mm (Japanese style) then 65.5 to 66mm (Wiseco) Good kit to do Stage 5 or 6. MB offer 64, 64.5, 65, 65.5 and 66mm.
CONS: Because of the layout of 150/175 cylinder castings, lower tunes are difficult to do with Suzuki pistons using a standard 107mm con rod, which gives a large inlet port timing and or oversized transfer timings as well which will not run right or give a lot of spit back. Expensive, as it requires a new crankshaft, bearings and ignition, requires a lot of machining work to be carried out to the cylinder. Extra machining to the cylinder base makes exhausts difficult to fit.

Change the crankshaft to GP then use a Yamaha con rod (110mm).

PROS: Excellent strong kit, good piston as above and rod set up ideal for stage 2, 3, 4, 5 and 6 tunes, by using the longer con rod less machining is required and improves inlet port timing.
CONS: Expensive requires crankshaft or con rod swap, bearings and ignition change. Could need exhaust modifying to suit the machined cylinder.

Change the crankshaft to GP then use a Yamaha con rod (115mm) this then requires a cylinder packing plate. Or use a standard or uprated 116mm con rod crank shaft.

PROS: Excellent quality piston kits as above with a good selection of oversizes 64 to 66mm. Good kit to do Stage 2, 3, 4, 5 or 6.
CONS: A little more expensive due to the piston, crank or con rod swap required, this is the preferred way to do a 190 conversion.
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