Building a 1981 Yamaha YZ465 Factory Replica...

OK, fair warning, I am really going to beat a dead horse in this section!

------------------ Top end continued

During the time the cases and top end were apart, I made some effort to consider how the Yamaha OW factory porting methods (shown earlier) could be applied to the YZ465 / 490. Of course this would be for future modifications to another motor as the top end of the current motor has already gone back together.

This is interesting to me because many of the methods used in the factory OW’s were closely held secrets back then. So it is fascinating now to be able to look back at what was done and how some of the same methods have turned up in later production race bikes. In fact, I found several photos of big bore MX cylinders and competition snowmobiles that will be included to illustrate this point.

In any case, two questions came to mind after studying the photos of the factory OW cylinder photos and how they may relate to modifications of the 465.

1) Can the two additional intake to transfer ports be added to the 465 cylinder?
- We already know the answer is yes as LOP cylinder shows this. Still I think it is worth taking a closer look especially when comparing these early implementations to those in modern big bore cylinders.

2) Can the OW style case induction port be added?
- To answer this we can look at the cylinder to case interface to consider what is possible.

To refresh, here again is the OW cylinder where the new ports in question have been labeled.







New intake/transfer ports

The next photo better compares the OW cylinder to the LOP 465 cylinder where the top row is the OW cylinder and the bottom is the LOP.

The red arrows show the corresponding intake to transfer ports. The blue arrow points to the case induction port in the OW cylinder and where we would like it to be in the 465 cylinder.




The OW cylinder is thought to be from a late ‘70s (pre-watercooling) 250. The LOP 465 photos (bottom row) show the addition of the intake/transfer ports like the OW. I was later to find out that these are called "Boyesen Ports" after inventor Eyvind Boyesen of dual stage reed valve fame.


It turns out the ports in both these cylinders are relatively small compared to photos of newer model production cylinders like CR500 and others that I have found. Unfortunately, making these ports much larger in the 465, without breaking through the side, would be difficult due to the location of the cylinder studs and the clearance needed for the stud nuts.

Perhaps LOP has defined the limit on this?

Case Induction
Regarding the case induction port question, the first thing I tried to do was find another example of this, especially one with photos showing the engine case side as I do not have a photo of the OW engine case. I was lucky to find this example,





The left photo above shows the induction port on the engine case side. It is milled to some depth below the base gasket surface.

The right photo above shows the base of the cylinder. The induction port is milled from the base right through to the intake port. Notice too how the intake side of the sleeve is cut back near the induction port.


This cylinder also has the LOP/OW style intake to transfer ports (although they appear much larger). I believe this is a good example of how to go about adding the case induction port to the 465 motor.

----

Now let’s look at the YZ465 case to cylinder interface where the cylinder to case induction port would be. The upper left picture shows the area in question and where any modification would take place.



On the case side, there is danger of milling through the crank case and into the transmission cavity (very bad!). A possible region for milling of the case and cylinder is shown in the lower left photo. This region, in green, leaves just enough surface area in the case for a good seal when the case halves come together.

The above right photo shows how the sleeve might be cut away. Only half the region is colored in green (along the case centerline) so the width of the cutout would twice shown.
Note that the sleeve cut away is in an area corresponding to the skirt cut away in the piston. Cutting the sleeve in this area does not reduce support for the piston skirt.

So, given the above, it does appear that both OW style port modifications could be applied to the 465.


Take a break now with a few photos. Here is Lauren Offner of LOP on left,

I did a search for big bore MX cylinder to see have far things have come since the OW and YZ465 days.

Here are some examples to compare with the previous post.

First is this aftermarket cylinder for the Honda CR500. Observations include,
- Large “OW” style intake to transfer ports (missing in the YZ465)
- No case induction port.
- Water cooling
- Exhaust power valve
- Two small auxiliary exhaust ports
- Six transfer ports plus boost ports (from the intake)




The Kawasaki KX 500 cylinder is also impressive.
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It has,
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- Large “OW” style intake to transfer ports (missing in the YZ465)
- No case induction port.
- Water cooling
- Exhaust power valve
- Auxiliary exhaust ports
- Four transfer ports plus boost ports (from the intake)



And finally, here is a radically ported Yamaha snow mobile cylinder



Ok, so here are a few oldies!

I raced against #622 in several classes during the '70's. Here he is at Bridgehampton in 1978
He was a really nice (and fast) kid!



And a photo of another good friend taken in 1979... now we ride together again as old guys!



This is me on taken on the same day and place as above. Looks like we are taking different lines.

Hey, check out #122 on the YZ465 ripping through the field at the 2012 ISDT Reunion Ride

Anyone know this guy ?

That guy is a goober, here is his story:

http://www.advrider.com/forums/showthread.php?p=20029543#post20029543

By the way Kevin, thanks for the tip on the YZ kick starter shaft. I got it in the other day and it looks like a heck of a lot better than the one I took out of the bike!

So glad to see that you stuck with this project and kept it going, while I completely fell off on mine.

I have a 1980 YZ 465 and I have a REALLY nice set of gold rims to put on it, but when I went to put them on my break hub won't fit on the gold rims (about a 6 1/4" hub) and my gold rim is a 5" hub. - I think the gold rims fit a 1981 YZ 465 (which is a 5" hub!) Could you tell me if I am right or wrong on that? and also the axle pin is bigger on the gold rim Thank you!

~Jenn

Well, I have been a little slow on the updates myself. But dont be too hard on yourself, I am sure you will get back to it when the time is right!

Kevin

Welcome and congratulations on you ownership of an '80 465. I am assuming you are talking about the rear wheel?

Wait here while I take some measurements....

ok, I am back. The 465/490 rear hubs measure about 5 7/8 inches diameter across the steel brake drum. I am not sure where you are taking your measurements but try comparing to that.

You may want to verify the stamping on your rim to make sure it is not for a YZ125 or 250. The YZ465/490's should be stamped 18 x 2.50.

On the axle diameter. The 1981 and later axles are larger diameter. I fitted a yz 490 rear wheel into a 1980 yz 465 swing arm but it required milling the axle slot to accept the larger axle spacers etc. You have do something about the brake plate too. If you look back a few pages you will see the modifications I did to mine. Should be right around here http://advrider.com/forums/showthread.php?t=772033&page=2,


Hope this helps, let us know how it turns out!

It has been interesting to look and compare photos of the 465/490 cylinder and porting to the later model engines.
I was thinking that these later motors could provide some guidance for future modifications of the old YZ's.

I mean, why not just copy the porting of the kx500 or cr500?

To see if this was reasonable I spent a little time collecting bore and stroke data from various big bore two strokes. If the stoke is the same as the YZ, then perhaps the port area and timing could be copied over as well... unfortunately, I found no other bike has the exact same stroke.

In any case, here is the table I made that lists the bore and stroke dimensions for the yz465/490 (in all oversizes) and the other big bore two stroke motocrossers. Dimensions are given in metric and english units. The bike with the closest stoke to the YZ at 82mm is the Maico 490 at 83mm.




There is one other interesting point from the table, that is, the standard yz490 piston is equivalent to an 8th oversize for a 465. Can those worn out 465 cylinders be saved by boring to 87mm?

Please let me know if anyone has tried this .

Books and other resources... continued

So straight forward (if there is such a thing) copying of another makers porting is not so straight forward . So with that I began reading up on two stoke engine theory. There seems to be several good books on the topic, here are a couple of the more popular ones,



The Two-Stroke Tuners Handbook can be downloaded free from a couple of sources (google is your friend). I found the Grahm Bell book to be pretty good too (about $25 on amazon).

If these books dont put you to sleep, try the Eyvind Boyesen patents on porting and reed valves...
http://www.google.com/search?q=Eyvind+Boyesen+port+patent&rls=com.microsoft:en-us:IE-SearchBox&ie=UTF-8&oe=UTF-8&sourceid=ie7&rlz=1I7DKUS_enUS265#hl=en&sugexp=les%3B&gs_nf=3&gs_rn=1&gs_ri=serp&pq=eyvind%20boyesen%20port%20patent&cp=15&gs_id=3&xhr=t&q=Eyvind+Boyesen++patent&pf=p&sclient=psy-ab&safe=off&tbo=d&rls=com.microsoft:en-us%3AIE-SearchBox&rlz=1I7DKUS_enUS265&oq=Eyvind+Boyesen++patent&gs_l=&pbx=1&bav=on.2,or.r_gc.r_pw.&bvm=bv.1355325884,d.dmQ&fp=cd9fa48ec9efd9ad&bpcl=39967673&biw=1189&bih=720


After reading these, the take away for me is that blue printing is about the best I can shoot for with the finite time I have. Yamaha knows quite well what they are doing (certainly more than me) and it would require a great deal of effort and experimentation (access to a dyno) to improve upon the original design.

Also when I look at what a guy like Eric Gorr charges for port work, it's a bargin compared to the time it would take to replicate his know how from scratch.

So my focus was and remains a high quality, reliable rebuild with focus on proper running and jetting. Sometimes I simply forget the bike is too fast for me anyway .

Still, it would be fun to take port area/timing measurements, crank through the equations, and see how the yz design stacks up agaist the recommendations of these books. If I get through all of this I will be sure to post the results here.

Next up will be pistons and the rest of the top end.

First, recall this bike was stolen and then recovered, here is a recent picture after repairing the (minor) damage. The thieves never started it so I am happy to say it still runs great!

FJ,

When you return, if you could look at this thread it would be greatly appreciated: http://www.advrider.com/forums/showthread.php?p=20489910#post20489910

Well, you could do a lot worse than having a motor with similar specs to a Maico 490. I believe using a standard 490 piston is a common practice in 465 motor builds, which gets you purty close the Maico 490 B/S ratio.

EG loves old school 2 strokes. When I talked to him last year he was getting ready to join Millennium Technologies last November and his prices were getting ready to go up. Still, he can build a 465 to do just about anything you want from the motor.

Your bike looks awesome! Did you find any swingarm wear at the shock mount location?

I have a little free play at that location on mine and I'm looking for a way to fix it? Drill and sleeve, Weld and re-drill?
I haven't found a kit anywhere but there probably is not one since no bearings?

Thanks Frank!

There are bushings lightly pressed into the swing arm at the shock pivot. These are replacable although I dont recall if the parts are still available from Yamaha. Sometimes the pin can have a little wear also.

Not too long ago I bought some bronze bar stock from Enco. I am intending to make a bushing for the clutch cover kick start hole someday. You could use the same material to make bushings for the shock pivot.

Good luck with your bike.

Kevin

Over time I have collected a fair number of new and used 465 / 490 pistons of various oversizes.



Some are OEM Yamaha and some are Wiseco. Wossner also makes pistons for the 465/490 but I dont have any of these.

The Yamaha pistons are cast pistons while the Wiseco's are forged. The cast pistons expand less than forged pistons as they heat up. Yamaha specifies ~2.5 to 3.5 thou clearance in the various 465/490 manuals I have with the larger 490 piston at the upper end of that range.

The forged pistons are claimed to be stronger and lighter but require greater clearance or they will seize when hot. I
had trouble finding clearance specifications for the wiseco but I did find a application note from JE pistons that gave guidance on clearance for their forged pistons. The clearance they spec varies according to bore size and application but for a yz sized piston it seems to be around 4-5 thousands.

This seems to agree with what I see in my IT490 with 1.5mm wiseco piston. Knowing about the greater expansion rate of these pistons has made me more inclined to let the bike warm up before really cranking on it. I have not had any problems with mine but can understand how one might experience seizures if a wiseco was used with Yamaha OEM clearances.

With all these pistons around, I thought I would weigh them to see how much they varied across bore size and between vendors. I used an old triple beam balance that I calibrated against the weight of 10 pennies.



I measured each piston with rings, wrist pin and bearing (the wiseco rings are thinner than the OEM yamaha's).

Here is a table with results I have so far. Columns are listed for Yamaha, Wiseco and Wossner. Rows are for 0 through 8th oversize.

"Yes" means the listed oversize is available but I dont have one to weigh. Otherwise I list the weight in grams. Red indicates the oversize is not available for that particular vendor.

There is one case where I have a yamaha and wiseco piston in the same oversize (490, 2nd over). The wiseco piston kit is about 12 grams lighter than yamaha.

So as mentioned earlier in this thread, I wound up running a 1mm oversize YZ465 cylinder giving 476cc.





One thing to watch out for is the base gasket. The later version Yamaha (and some aftermarket gaskets) have a sealer as shown below. This is an improvement on earlier gaskets with no sealer.I became aware of this issue when my IT490 developed an air leak using one of the earlier gaskets.



The cylinder head was painted in silver enamel and baked in an oven.



And then the motor, with assembled top end, was bolted back into in the bike.



The stator plate was pretty dirty...





I used contact cleaner to clean the plate and various ground contacts. I also cleaned and checked the mounting screws and wiring harness. I did not go overboard on the coils as I did not want to stress the wiring or insulation.






After cleaning, the stator was mounted to the engine and the timing marks were aligned as specified in the manual.
Both crankshaft and flywheel tapers were carefully cleaned. A light grinding compound was then used to lap the tapers together to ensure a tight fit. The tapers were cleaned again and a new flywheel key was used when mounting the flywheel for the final time.








I could not find my flywheel holder tool so used the old tie down flywheel holder trick.

Using a tie down, hook one end to the frame then make a couple of wraps around the flywheel like this



Hook the other end of the strap and pull up tight.



Then use one hand to put weight on the strap to tighten and hold the flywheel from turning while you tighten the flywheel nut
with a torque wrench with the other hand.

Sorry, but with both hands occupied, I could not get a photo of this final step .

My last motocross helmet was a nice Bell Moto 3. Unfortunately, the foam in the liner disintegrated over time. Thinking my mxing days were behind me, I threw the darn thing out sometime in the late '80's!

That was a great looking helmet and the one I buy today if I still could.

Most of the new helmets dont appeal to me because of the crazy graphics and odd color schemes. So instead of buying a new one, I picked up nearly new Bell Moto 5 that I have been using for the last 2 years. But even though it was in good shape, it is an old helmet and past its prime I am sure.

Then I found this reasonably priced ($107) HTC helmet with both DOT and SNELL 2010 approvals. I believe either AHRMA or AMA will require snell 2010 this year. I am not sure if they actually check this at the races but didnt want to have any problems.

The HTC iscomfortable and a good fit. The best part is that it is plain white. I was not wild about the visor so decided to mount a traditional Paulson Moto Peak visor in blue. The goal was improved safety with old school looks.

The Moto Peak visor is not a direct replacement. New snaps are required to make it all work. Here are the steps

Helmet with new fangled Gen Y visor,




Old school moto peak like I last used 30 years ago,



Note there are 3 - 6mm screw holes in the hjc helmet to hold the factory HJC visor but no provision for a standard type visor.

Therefore it is necessary to mount five snaps to the helmet. I found the snaps to be available from the Motorcycle Superstore (3 snaps per package).

The snaps come with screws to mount to the helmet. I placed the visor up to the helmet and marked the desired snap location with a pencil. Then I drilled a hole for the snap screw.



Four of the five screws are mounted in this way. However, the center snap had to screw into the snap location as the original 6mm scew.

The work around was to cut a short section of 6mm screw to use as a stud to fill the original 6mm hole. A small hole was drilled into this trimmed 6mm stud for the new visor snap screw. The trimmed 6mm stud was screwed into the helmet and then the snap was then screwed onto the stud.

I actually did the center snap first as I wanted to make sure it would work before drilling holes in my new helmet



The next photo shows the helmet with all five snaps.

The visor is vertically slotted at the center snap and so accomodated the offset center snap position as dictated by the original 6mm hole while allowing me to have the visor angle I wanted.




Anyway, it all went pretty smoothly and gives me a new helmet that looks a little closer to something from 1980.

This photo show a comparison of the HJC, a Bell Moto 3 and a Bell Moto 5. And yes, I do have Bell stickers to go on the HJC




Now check out this guys helmet



And some more Moto 3's

Kevin,

I just received my 2013 AHRMA Handbook. Under section 3.3 Technical Inspection sub section 3.3.2 it states that Snell M2010 helmet are required for ONLY road racing and dirt track. All MX, PVMX and Cross Country must meet Snell M2005 or equivalent standard.

So in those respects you are good to go. Unfortunately, you modified your helmet and in the same section it also states that ALL helmets will be closely inspected for ANY damage OR modifications to the shell and inner liner. Any damage or modifications (to include non-OEM visors) to the helmet found will be grounds for immediate denial or disqualification from any AHRMA event.



























...just kidding about that last part

Haha, lucky for me I saw your last sentence first before reading the first part. Otherwise, with the way things go these days, I would have believed!

BTW, I had a good time at the York PA swap meet a couple of weeks ago. Seemed to be a good turn out with lots of parts and bikes up for sale. They had an auction for the first time too. I was too busy to watch much of that but it looked like fun and folks were bidding. There were bike for sale out in the parking lot too.

This Montesa looked pretty good,



Here are some Hondas out in the parking lot.








Some top notch show bikes were on display indoors,





This Elsinore was in the auction as were the bikes behind it.



My understanding was that all the following bikes, with number 46, were from the same family