New Member Opening a Big Can of Worms

[ny.phill]

I would think that any used gears would most likely not have the backcut in them, right?

IIRC from what I read last night, new gears will have the backcut from the factory so I'm not sure it pays to get used gears as I would still need to do the cut myself. Once i get all the prices together I don't think it'll be too difficult to see where the bast bang for the buck is.

And of course considering I could need bearings, rings, valve seals and who knows what else it's probably best to keep digging to see what i'm dealing with. Sure is nice to have some hard parts in hand at this point tough =)

[bikerphil]

Cheapest place AFAIK for new back cut gears...

http://www.yamahaaccy.com/parts.aspx

[crazy steve]

No, only the new replacement gears had the back cut as far as I know. They cost roughly $100 each, so that isn't a cheap fix. And be aware that new engine parts for these is hit-and-miss at best; while a lot of parts are still available new (although new OEM can be outrageously expensive; $150 for a head gasket!), many parts have gone obsolete. Particularly pistons and rings; there's been a number of searches for a viable interchange, with no luck; the only 'commonly available' pistons/rings are the Wiseco 'big bore' kits (at about $600) so doing an actual rebuild on these can be a bit expensive.

Given the number of these that are being parted out (many running bikes), it's generally far cheaper to find a good used motor if yours is worn or damaged to the point of needing a complete overhaul.

[ny.phill]

Just checked out that site bikerphil and it has been bookmarked... yeah, they run for about $120 a pop there for the 1st and 4th gears, but of course now I'm wondering if I need to replace 1st gear as the dogs are on the 4th gear. You guys think the lands on the 1st gear are worn too bad also?

As for the engine, I came across a post before where someone was saying he had a "well duh" moment when his compression test #'s were way low as he realized he didn't have the throttle open. I've never had the throttle open when i did a compression test so now i'm hoping it's not as bad as i thought so hopefully that works out.

I also saw a post about trying to track down the Hastings rings and it sounds like they got a ring set that's pretty close for $45 though it needs some work. I'm pretty sure you were in on that thread Crazy_Steve so I'm not telling you anything you didn't know already, but figured it was worth mentioning.

Thanks again for all the advice guys. Should have some bearing pron for you guys tonight if all goes well =)

[crazy steve]

As for the engine, I came across a post before where someone was saying he had a "well duh" moment when his compression test #'s were way low as he realized he didn't have the throttle open. I've never had the throttle open when i did a compression test so now i'm hoping it's not as bad as i thought so hopefully that works out.

It makes a big difference as whether or not the throttle is open, so rechecking is good. I'll note that you can check compression with the carbs off too (if the motor is out of the bike) by simply connecting power to the starter to spin the motor, but expect a much higher than spec number if you do; I checked one of mine, and got numbers in the 200 lb range.

[cywelchjr]

It makes a big difference as whether or not the throttle is open, so rechecking is good. I'll note that you can check compression with the carbs off too (if the motor is out of the bike) by simply connecting power to the starter to spin the motor, but expect a much higher than spec number if you do; I checked one of mine, and got numbers in the 200 lb range.

That seems high even for that. If the throttles are wide open, that's pretty much the same as no carbs are cranking speed. I have however always understood that carbon buildup in the ring are can increase compression and cause detonation. It's also possible in that case that just running the engine under normal operating conditions where it gets hot enough to burn out the carbon can fix that too.

[jetmechmarty]

I bought a set of gears for mine and haven't changed them yet. That's one of my winter projects.

I just priced the 2nd gear wheel at $111. www.yamahasportscenter.com

I don't remember spending that much, but.... what else can you do?

[crazy steve]

That seems high even for that. If the throttles are wide open, that's pretty much the same as no carbs at cranking speed...

Cy, you forget that even with the throttle open, the slides are down, blocking 70-80% of the opening....

[cywelchjr]

Cy, you forget that even with the throttle open, the slides are down, blocking 70-80% of the opening....

I dare you to get any vacuum at all under those conditions at cranking speed. You're not pulling enough air at cranking speed for that restriction from the slides to slow the air down at all.

I'll bet if you took readings with the carbs on and the throttle wide open, and then with them off it would be the same reading.

[CatatonicBug]

I wouldn't pay a machine shop to do the dremel fix, but I agree that your gear is just about past the point of no return... Maybe member Andreashweiss has a full set he'll sell? I know I've seen full sets of used/nice tranny countershaft gears go for around $100.

[Guy_b_g]

These bikes are getting old enough now that you may get lucky and get a set of gears that are either factory replacement (with the back cut dogs) or ones that someone has already done the dremel fix on, if you look closely at the ones for sale on Ebay. I bought a grab bag assortment of parts on Ebay a year or so ago, with transmission included, and low and behold...a full set of factory backcut gears! Cost me about $40. Look at the pics, or ask for close up pics of the trannies on Ebay and as I said,,,you may get lucky...just a thought..

[ny.phill]

They should call it AwesomeBay

Wanted to give an update as I saw the two differing sides of our old Yamaha's today. First, the evil side. I spent $10 for a single bolt (alternator rotor remover and i'm actually happy to have it for $10) which was followed by being priced at $200 for replacement gears at my local Yamaha dealer. Ouch. I know I can get new ones cheaper, but still... I don't like to hear prices like that.

Of course, a few hours later I came across the good side. I found out that I won an eBay auction for a complete countershaft assembly for the bargain basement price of $26 shipped. Love the ebay sometimes, so great!

Doubt it's backcut, but that's alright, i'm still quite pleased =)

I've been doing some reading on final drive and 5th gear mods being as I have everything apart anyway... the FD mod seems pretty straightforward if I could get one at the right price, but are there any comparably well done directions on the 5th gear mod? I'm still kind of confused what the outcome of a lot of threads were if there even was a final outcome.

[bikerphil]

AFAIK, nobody ever finished that mod for a taller 5th gear. The 750/850 mod is a good one though, it'll drop your rpm's by about 850. Glad you got some better gears to work with.

[ny.phill]

There HAD to be something ugly in here

Ok, at least I'm not missing anything with the 5th gear swap. That really does sound like the ideal situation.

So after some difficulty, I got the alternator rotor off and after cracking the cases I realized it's better kept together till i got the top end off.

Off come the cams, the heads, and finally I just got the jugs off. As you can see, I was rewarded with a somewhat trashed piston skirt. Damage is very similar on either side of the piston and the sleeve. The other three look pretty good and the few bearings I got to see prior to pulling the crank look to be in good shape also. I'll plastigauge later.

What would say is my best approach here? Or should I say "most cost effective", i'm poor as dirt =)



#4 piston - shreddage



#4 sleeve - matching shreddage


the lovely mess i gone and made

[natemoen]

Ouch. Could put on new jugs and piston. Could talk to the resident parts man andreas and see what he has for parts right now.