conrods

morning, does anyone run there engines with a t&g uprated con rod kit..

I run one in my 185 longstroke. We used a larger 22mm crankpin (like the TZ250 ones we made for 125 short stroke) with a silver plated RM125 cage, TZ250 thrust washers etc; so it has a stiffer and high rev safer bottom end. It has done 15 hours with no greater detectable play, will measure with micrometer when it comes apart in summer hols.

Hi yes the bike that morgan Thomas is riding has one in if that's any help

thanks for replies

I have one in my road bike, seems OK so far-though I've barely done 100 miles on it.

hello, could anyone shed any light on a big end failure. the bearing rollers are longer round but are flat and the cage and the big end journal are a dark grey/blacky blue colour. the bike first started no probs ticked over for approx 5mins and the bike travelled about 200 yards before tightening up and cut out...i had been running with a standard rod in a standard crank and a small brass bush(rex caunt) enabling me use the pe 175 piston with no probs. i finally got round to installing a new set up along with steel clutch arrangement.and hopefully gear change fix... have i messed up with the crank install? i believe that the big end is lubricated only by the fuel which at present is leaded and at 20:1 mix... or am i just unlucky... (ill bring the conrod/roller bearing to the next meeting to show)..... any pointers would be very much appriciated.

Hi,

If the rollers are flattened and the cage and pin is blue / black then its fair to say that the bearing has jammed , with disastrous consequences.
What state are the thrust washers in ? Are they complete or chewed-up too ?
How much float did you have on the big end / thrust washer assembly ?
Regards,
Jon

hi, i havnt had the thrust washers returned to me only the con rod bearing and crank pin, as to the conrod big end float ive no idea. the crank was put back together by the supplier and i fitted in the engine. ive had a new one put in the crank but im reluctant to use in case im not installing the crank assembly correctly and have the same result... i do have a standard crank im thinking of using just to see if this runs ok with before trying it again.do you think that lubrication would have caused this failure?

nobby1 wrote:

hi, i havnt had the thrust washers returned to me only the con rod bearing and crank pin, as to the conrod big end float ive no idea. the crank was put back together by the supplier and i fitted in the engine. ive had a new one put in the crank but im reluctant to use in case im not installing the crank assembly correctly and have the same result... i do have a standard crank im thinking of using just to see if this runs ok with before trying it again.do you think that lubrication would have caused this failure?

Could be lubrication. When I put my engine together I got a syringe from a printer refill and used it to squirt loads of 2T in both bearings. Did it turn over OK when you put it together? I'd have thought it would have gone a bit further if it was OK to start with.

the bike ticked over fine didnt seem to be any problems. went smoothly for the first 150 yards then as i slowed down to cross a t junction and then opened up the throttle to continue it hestitated and i felt the engine tightening up and then cut out. got back to the garage tried to re start the engine but the grating noises coming from it led me to believe there was a major problem.... ive managed to drag myself from the pit of dispare and decided to put the engine back together today and can only flood the bearings with 2 stroke as you say and hope that ive just been unlucky with maybe a faulty big end bearing first time around...

Hi Nobby1!
This bit of info may be absolutely no use to you whatever. Derek Neil
prepared our Bantam engine and a big-end seizure (at Snetterton) -- first season out -- he reckoned was attributable to the roller-cage. Either its weight or its outer diameter were too great for the revs it was doing. If memory serves me correctly Derek reckoned the cage overheated because its outer surface was rubbing too hard on the inner surface of the big-end eye. I know the cage was skimmed smaller and I seem to remember a relieved section in the middle being made (by Les White) so that the rubbing was on two tramline surfaces, wide apart. Seemed sensible to me that petroil had a sort of reserviour there. In any case with that engine´s big end so modified it lasted several saeson of hard racing -- although it had to remembered Icarus I´s motor only revved to 8400rpm with wind behind.
Engine pictured here...
Good luck!
JayBee ....

Hi Nobby,
You seem to be describing a classic lack of lubrication, but this problem can be caused in a number of ways.
1. No oil in the fuel.
2. No pre lubrication of the big end on assembly.
3. Side to side float of big end is too small so washers nip and overheat rapidly. Side float needs to be massive to allow lubrication down the side of the rod. (this is the most likely cause as it may have been pressd together with the standard clearances.)
4. Assembly using grease as the initial lubricant.
5. Bad big end cage.
6. foreign objects in the assembly can start the problem off.

Hope this helps and you get moving
Cheers,
Alan

thanks for all the replies and advise. i noticed the crank end float has changed again when i went to shim it up last weekend, so i stopped and ive bought some more shims. ill bring the crank assembly with me on the weekend meeting and would be grateful for someone to tell me if the big end float on the conrod is good enough before i re assemble engine again...