Suzuki 2 Strokes

i recently stripped a ramair crank down to replace the seals etc and found these conrods in it. this is a generic photo, but my conrods are exactly the same. they are from a mid 80's yamaha yz125. anybody ever seen this before? i certainly haven't and i've stripped hundreds of gt250 engines. they seem a lot more substantial than the standard gt250 rods, so i thought it might be a common proddy racing trick? anybody know?
cheers, dd.

Your pic link didn’t work.

But that’s interesting.
T250 & GT250 has 54 x 54 bore & stroke
T350 has 61 x 54
GT380 has 54 x 54
YZ125 has 54 x 54.5 (for 2004: http://www.bikez.com/motorcycles/yamaha_yz_125_2004.php)

what link? i get the photo straight up on the post - odd
i did some googling about and noticed the yz was 54.5mm stroke. perhaps the big end on the yz uses different bearings? just guessing here, and if i scratch my head hard enough i seem to remember this engine [a gt250k] having 2 head gaskets each side, which seemed a bit daft to me at the time. i measured a gt250k conrod end to end and according to my little metal ruler it was 140mm and so was the yz rod and as near as i could tell the centre of the big end eye to the centre of the little end eye was the same on both sorts of rods. hmm thanks for the reply anyway
cheers, dd.

The second head gasket likely was intended to deal with the additional 0.5mm connecting rod length.
I’m certainly no expert on this, but I’m inclined to think that it would be better to use multiple cylinder base gaskets.

The pistons in the bike might not be for the GT250K.

hi jab, they were definitely gt250k pistons on a +0.5mm. they were scored to hell on one side, as were the barrels. looked like one circlip each side had come out - somebody using old circlips or didn't put the new ones in properly threw the pistons in the scrap bin and put the barrels aside for a rebore, as the exhaust threads were good [for a change]
cheers, dd.

Shirley, conrod length wouldn't affect stroke, it would be crank tbrowthat gave the extra 0.5mm? The piston would only move the same distance, but slightly further up the barrel, hence thicker head gaskets. Mike Yeadon had a crank done and the company fitted (I think) KTM 125 rods which were 0.5mm longer and caused 'conflict' (read 'hitting!') between piston crown and head.
Are the ports or pistons modified on the engine as they would be operating slightly differently if the pistons were 'higher' in the bores at any crank angle compared to standard rods? Thicker base gaskets would put that to 'standard' as jab suggests.

hi alan, i measured the rods against each other with my battery powered length doohicky and they were very close, something like 140.232mm against 140.234mm so i'd say they were the same length. the 16mm little ends fit perfectly in both, the big end roller and crankpin fit perfectly. i mean for all i know they could be an aftermarket product specifically for the t250 and early gt250? unfortunately there's no markings on them anywhere. the pistons were scrapped years ago and i must have 5 sets of barrels with scores in them, so i couldn't really check on the ports. the only reason i asked this question is because i was going to use them on MY NEW PROJECT btw, don't call me shirley
cheers, dd.

Sounds like those rods are a good swap for OEM Suzuki, 0.002mm difference in length is probably well within Suzuki's production-line tolerances ...

As Mike said, the YZ Yam will get the extra 0.5mm stroke from the position of the big-end pin relative to the crank centre.

hi craig, i think you mean alan, not mike but i think he's right. i just can't remember when this engine came to me. i keep records of all my engine numbers, size of bore, size of little end, but not where i bought them from. bit late now after 40 years
anyway, here's a photo of my rods, the yz type and a normal 250k.
cheers, dd.

Apart from the extra machining around the big-end eye, they look identical ... that extra machining is probably good for big-end lubrication too

hi craig, the big end is a lot heftier, slightly wider and much thicker. when i get back up the shed i'll weigh them for comparison. i'll edit this post when i've done it.
cheers, dd.
right, i weighed both.
yz type are 494 grams each
gt type are 420 grams each.
so quite a difference

DD,

What is the Part # for the YZ125 rod if you know? What year yz125. If that truly fits a GT250K/T350 that is a sweat find... getting hard to find the early GT250 Con Rod.