Engine rebuild - take the leap?

[fatfreddy]

Hi,

So after much procrastination and lurking on this forum, my Swedish 250LC is has been stripped down, frame and other bits powder coated and a large order (no doubt the first of many) has arrived safely from Norbo.

The big question is, to what extent do I rebuild the engine? It had 30k kilometres on it and has had one rebore and, to my untrained ear, seemed to run fine when I got the bike.

Alternatives are: top end refresh with new pistons etc. or do I go the whole hog (first time for me) and split the cases and do the lot? And what about the crank? Can you tell if that needs a rebuild or is it a case of you pay your money (or not) and take your chances?

Finally, if I do take the plunge, what the collected wisdom on seals, gaskets and bearings? Pattern or Yam and where is the best place to get them?

Thanks in advance!

[muttsnuts]

use only genuine Yamaha crank seals, gearbox bearings some are only Yamaha supplied anyway, others will be fine if you use a decent make, a decent gasket set like Athena is ok and then the question about head gasket, research it, its been done to death on here

Crank, get it checked while its out, will save you time and m onety later, have it overhauled if at all suspect, get the bores checked for wear, if in tolerance then a good hone and a new set of pistons rather than rings will see it run for many more years etc, if out of spec, get it rebored

HTH

[Yogi]

Definitely split the cases,get the crank checked,
you can then check all the gearbox components for wear and most importantly you can replace the crank seals which are probably on there last legs
Norbo can sort you out with all the gaskets and seals and even the three spec tools you'll need
Makes sense while the engines out for peace of mind
Matt

[oldelsieboy]

Ideally a full strip & rebuild is recommended but on the other hand if it ain't broke, don't fix it.

Bear in mind, a crank rebuild, rebore, new pistons, seals, gearbox bearings, gaskets etc might cost you as much as £600

OEB

[davey]

If you go for the full rebuild research and make sure you have all the parts and tools before you start , this will save time .
My stumbling block as i just completely rebuilt mine was that my torque wrench was fine for the big stuff however you will need a wrench that goes low ft lbs for the casing halves on reassembly and the clutch .
Im not a mechanic but found it very straight fwd to do a motor , take lots of pics if you think necessary , in fact take em even if you don't .
My crank was goosed but while it was torn down i changed the WP bearing and impeller , clutch friction plates and all the seals through out .

[fatfreddy]

Many thanks for all the advice!

[bare]

At 30K kms Both Crank and Bores ...will... need redoing.
Seriously surprising if not.
Annoyingly: If the thing was a 4 stroke with 3x the wearing parts It would just be broken in at that mileage.

[sp885]

Hmmm something for me to think about here then, my 350LC has done nearly 25,000km, It's had a top end rebuild just before I got it at around 21,000km but nothing else engine wise as far as I know

[4l04ever]

The life of an engine will also depend on the amount of abuse, quality of oil and other consumables (seals etc). I have seen bikes with over 40k miles which have never been rebuilt, but there have been others that have died in less than 1000 miles.....

Make sure you do a leak down test whether you rebuild it or not, to make sure there are no air leaks, as they are a major cause of two stroke death!

[jackjabba]

Hey Freddie just make sure your cat doesn't shit in your headphones.




You need to read the comics to understand.

[midlifecrisisrd]

Hard to tell what it will need

Depends how much piece of mind you want. A newly built engine will last for years and many miles.

Having to strip it all to bits after 1000 miles is soul destroying.

Last 2 ypvs motors I stripped surprised me

1st had 29k miles on it and was on standard bore. Ring gap measured within 0.05mm of a nos barrel.

Crank was OK but near service linits on big end clearance and rod end deflection so was changed.

Conclusion was that the top end had been changed.

2nd had 26k miles on it and also on standard bore. Bores have wear and them but will live to fight another day with new rings.

Crank measures fine, well within limits

Conclusion is that it has had a very very easy life.

Will I strip the bottom end to inspect and chang the crank seals....

.....still not sure lol



Steve

[spondonchris]

If it was mine and it runs fine...for peace of mind re ring it, chuck some small ends in and go and enjoy it. No need to strip the entire engine.