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Old 04-12-2012, 02:27 PM   #55
FJ_Kevin OP
Gnarly Adventurer
Joined: Dec 2010
Location: Maryland ==> originally from Long Island
Oddometer: 365
Motor Rebuild:

With a lot of the chassis issues resolved, it is time now to move on to the engine. Over the last year more and more 465/490 parts have come my way. I have to admit...I had lost track of what I had in boxes and tucked away in another building .

To get started, I have posted a couple of photos where I am sizing up a few of the various parts motors/cases as well as the original motor on the work bench.

From left to right,
1) late model 490 cases,
2) 3R5 YZ465 bottom end
3) 4v4 (81) YZ465 bottom end
4) complete 3R5 YZ465 motor from my bike

Not shown is an 83 IT490 engine and 2 more complete 4v4 YZ465 parts motors on the floor!

Boy, things really have gotten out of hand here !

As I have been going through all these motors, it has been interesting to observe some common failures as well as design changes meant to address them. The kick starter mechanism is one example of a problem area that I will discuss here and in a future post.

There have also been several design changes to the clutch basket through the years. And for good reason too. The early model clutch backet has a pressed on kick start gear that can move over time. In a later 490 design, the gear is made integral with the basket to avoid this problem. I'll follow up with some photos that show all this.

In any case, for competition bikes this old, you really need to examine just about every part to be confident in what you have in the end. While most parts in the motors I examined were in good shape, it did seem that all of them had least one or more show stopping issues. And there were quite a few examples where previous mechanics? had gotten in there and hacked things up a bit .

Overall though, I think these are well made and very robust engines. Its also cool how Yamaha kept improving them and how many of these improvements can be retrofitted to the original 465 design.

The famous kickstarter case leak:

So moving on, one of the 1st things I noticed was how many motors had epoxy on them to seal cracks in the engine case at the back of the blind hole that accepts the kick starter shaft. I have come to find this is a very common issue. The only harm seems to be weeping oil which the epoxy is meant to stop.

The next 2 photos campares a good case with a case with the epoxy fix. A 3rd photo shows an engine case that has been severely busted out and welded back together, yuk!

Good case (notice no epoxy on kick starter boss - upper right)

Epoxied case

and broken/welded case. Whoah!

What's behind all this? ... I have several ideas but I'll have to post that next time

My '81 YZ465 Factory Race Replica

My Vintage Husqvarna/Motocross Restoration Extravaganza Thread
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