Learning to rebuild 4-stank

bierbower105
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bierbower105
My YZ450 just rolled 60 hours and it is time for me to learn how to wrench on thumpers. I'm pretty mechanical but I'm intimidated to start this one.

I have rebuilt 2 YZ125's frame up and motor (one crank) - just looking at my 450 on the stand makes me miss them. The piece of mind knowing you know every bolt on a bike is a really good feeling at the track if something goes wrong.

I have a pretty good relationship with my local motor folks so I'm considering doing a sit in session while they do a top end and take notes.


Do you guys have any books/info/videos you found helpful on your first rebuild?
Where can I pick up a full service manual? (for torque specs and details)
What are some good tools I should pick up that wouldn't be in a typical moto tool box? (flywheel puller etc.)
Any other top end parts I should replace while I'm in there? (I'm thinking just piston and cam chain)


Or just sell and buy another smoker....lol. Thanks in advance.
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Zeke27G
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Zeke27G 10/19/2020 7:12am
10/19/2020 7:12am

Was expecting some Stank Dog talk...
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Forty
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Forty 10/19/2020 7:13am
10/19/2020 7:13am
60 seems low. Maybe check tolerance, change fluids and recheck at 100.
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bierbower105
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bierbower105 10/19/2020 7:18am
10/19/2020 7:18am
Zeke27G wrote:

Was expecting some Stank Dog talk...
Stank dog rules - I like his WeBig gear more than expected.
bierbower105
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bierbower105 10/19/2020 7:22am
10/19/2020 7:22am
Forty wrote:
60 seems low. Maybe check tolerance, change fluids and recheck at 100.
I agree it might be early but winter is coming and I want to go for it while I have the down time.

The Shop

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walent215
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walent215 10/19/2020 7:23am
10/19/2020 7:23am
1. Service manual or PDF of one
2. Flywheel puller
3. Circlip install tool ( not completely necessary)
4. Shim kit
5. Calipers/Bore gauge ( bore gauge not completely necessary)

Dont be intimidated ! Its not near as bad as it may seem. Service manual can be had from online retailer/ebay etc.
You could go til the next piston replacement on a cam chain replacement but there so easy and inexpensive to replace . Plus ive found when doing the piston/ cam chain together its so much easier to remove/install the cylinder/head if you set timing then remove flywheel and cam chain first! makes the whole process much smoother!
Theres plenty of knowledgeable folks here that will be more than happy to answer any questions or walk you though something while doing this.

If you have any issues /questions feel free to reach out.
s.walent1@verizon.net
Text 760-608-1688
8
Dirtydeeds 10/19/2020 7:27am
10/19/2020 7:27am
When I first did my own back in 04, I read the service manual a couple times first that way I understood the whole process vs. learning it step by step. If you have any mechanical abilities it’s not that bad. Good luck!
3
erik_94COBRA
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erik_94COBRA 10/19/2020 7:29am
10/19/2020 7:29am
The number of parts and steps compared to a 2-stroke is what I think makes it intimidating. It really isn’t that bad, just time consuming.

Yamaha manuals are also generally very good IME.
2
wideopen198 10/19/2020 7:38am
10/19/2020 7:38am
What you want to do at 60 hours? Piston change and checking valve clearance should be enough. If you're pretty mechanical like you say, you should be able to do it when you follow the manual carefully. Most important thing is setting the camshaft timing right.
1
Boomslang 10/19/2020 7:39am
10/19/2020 7:39am
bierbower105 wrote:
My YZ450 just rolled 60 hours and it is time for me to learn how to wrench on thumpers. I'm pretty mechanical but I'm intimidated to...
My YZ450 just rolled 60 hours and it is time for me to learn how to wrench on thumpers. I'm pretty mechanical but I'm intimidated to start this one.

I have rebuilt 2 YZ125's frame up and motor (one crank) - just looking at my 450 on the stand makes me miss them. The piece of mind knowing you know every bolt on a bike is a really good feeling at the track if something goes wrong.

I have a pretty good relationship with my local motor folks so I'm considering doing a sit in session while they do a top end and take notes.


Do you guys have any books/info/videos you found helpful on your first rebuild?
Where can I pick up a full service manual? (for torque specs and details)
What are some good tools I should pick up that wouldn't be in a typical moto tool box? (flywheel puller etc.)
Any other top end parts I should replace while I'm in there? (I'm thinking just piston and cam chain)


Or just sell and buy another smoker....lol. Thanks in advance.
If you have 2 T building experience then the transition to 4T will be ok. Purchase a genuine YZ450 workshop manual and you follow it religiously. Good luck going forward.
1
bierbower105
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bierbower105 10/19/2020 7:41am
10/19/2020 7:41am
walent215 wrote:
1. Service manual or PDF of one 2. Flywheel puller 3. Circlip install tool ( not completely necessary) 4. Shim kit 5. Calipers/Bore gauge ( bore...
1. Service manual or PDF of one
2. Flywheel puller
3. Circlip install tool ( not completely necessary)
4. Shim kit
5. Calipers/Bore gauge ( bore gauge not completely necessary)

Dont be intimidated ! Its not near as bad as it may seem. Service manual can be had from online retailer/ebay etc.
You could go til the next piston replacement on a cam chain replacement but there so easy and inexpensive to replace . Plus ive found when doing the piston/ cam chain together its so much easier to remove/install the cylinder/head if you set timing then remove flywheel and cam chain first! makes the whole process much smoother!
Theres plenty of knowledgeable folks here that will be more than happy to answer any questions or walk you though something while doing this.

If you have any issues /questions feel free to reach out.
s.walent1@verizon.net
Text 760-608-1688
Right on - thank you, Will do.


bierbower105
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bierbower105 10/19/2020 7:42am
10/19/2020 7:42am
wideopen198 wrote:
What you want to do at 60 hours? Piston change and checking valve clearance should be enough. If you're pretty mechanical like you say, you should...
What you want to do at 60 hours? Piston change and checking valve clearance should be enough. If you're pretty mechanical like you say, you should be able to do it when you follow the manual carefully. Most important thing is setting the camshaft timing right.
Piston and Cam Chain. Check Valves.
Hudd_421
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Hudd_421 10/19/2020 7:56am
10/19/2020 7:56am
60 hours is a good time to do a piston on the YZ. Manual will walk you right through the process.

I doubt your valves will be out of spec, but get a feeler gage to check while you're in there.
You will need a fly wheel puller to swap the cam chain. The only tricky part is making sure you're at top dead center and getting your cams aligned at the timing mark, but it's not difficult.

A few tips:
read the torque on the head bolts instructions, it's not just a standard torque spec
Go oem, Yamaha OEM parts at Motosport are basically same price as a vertex/wiseco
stuff lots of rags into the case so you don't loose a circlip down in the case.

Aside from learning the nuances of timing, there really isn't much more to it than a 2 stroke!
1
FWYT
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FWYT 10/19/2020 9:21am
10/19/2020 9:21am
You can do it, no problem. Just what with more parts, keep things organized and follow the manual.
If I can do it, anyone can.
1
O&GDriller
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O&GDriller 10/19/2020 9:39am
10/19/2020 9:39am Edited Date/Time 10/19/2020 9:41am
I'm surprised you need to do anything at 60 hours. I'm old and slow but have gotten 200 hours out of my past 6 KTM 450's without ever touching the engine, including clutch. My son on the other hand is a fast intermediate and he's also gotten 200 hours out of his KTM engines without ever opening up anything.

We generally sell them at 200 hours for new bikes. It's great never having to touch a KTM engine. FWIW, prior to switching to KTM we rode Honda 450's and had to put top ends in at 40 -50 hours. Clutches generally before that as well as having to replace those junk Honda clutch hubs due to notching. KTM's never need the clutch basket replaced.

Note I'm not trying to start a KTM crusade/pissing contest but just sharing factual information...
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kb228
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kb228 10/19/2020 9:49am
10/19/2020 9:49am
If you can do a 2 stroke, you can do a 4 stroke. Theyre nothing to be intimidated by. Other than removing the timing chain its not all that different than a 2 stroke. Pull the head, pill the piston clip, wrist pin. Etc.. you know the drill.
2
bierbower105
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bierbower105 10/19/2020 10:05am
10/19/2020 10:05am
O&GDriller wrote:
I'm surprised you need to do anything at 60 hours. I'm old and slow but have gotten 200 hours out of my past 6 KTM 450's...
I'm surprised you need to do anything at 60 hours. I'm old and slow but have gotten 200 hours out of my past 6 KTM 450's without ever touching the engine, including clutch. My son on the other hand is a fast intermediate and he's also gotten 200 hours out of his KTM engines without ever opening up anything.

We generally sell them at 200 hours for new bikes. It's great never having to touch a KTM engine. FWIW, prior to switching to KTM we rode Honda 450's and had to put top ends in at 40 -50 hours. Clutches generally before that as well as having to replace those junk Honda clutch hubs due to notching. KTM's never need the clutch basket replaced.

Note I'm not trying to start a KTM crusade/pissing contest but just sharing factual information...
Bike runs like a top - but that's not the idea of preventative maintenance.

1
GeorgiePorgie 10/19/2020 2:53pm
10/19/2020 2:53pm Edited Date/Time 10/19/2020 2:54pm
Forty wrote:
60 seems low. Maybe check tolerance, change fluids and recheck at 100.
bierbower105 wrote:
I agree it might be early but winter is coming and I want to go for it while I have the down time.
If it’s not broke.....don’t fix it.

Why don’t you pick up a clapper 250f and rebuild it if you’re lookin to learn to wrench on the thumpers ?
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Pit Row

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captmoto
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captmoto 10/19/2020 2:59pm
10/19/2020 2:59pm
The man is an enthusiast looking for advice. There is some good tips here but the inevitable Vitards show up wondering why he wants to do this, buy a clapper or a KTM and never have to touch his bike again. FFS, it's not like he's asking if powder coat or anodizing is best for his nipples or who has the best billet oil filler plug.
Flame away Vitards!!!
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MotoX85
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MotoX85 10/19/2020 6:43pm
10/19/2020 6:43pm
Its really not as bad as you think. Pretty much the same concept as the 2 stroke.

The cams and crank are marked so its really easy to line up. ALWAYS replace the timing chain and tensioner when you do a top end, ALWAYS...... these are actually more important then the piston.

Since you own a Yamaha, you will probably never have to redo the valves and id be surprised if you even have to adjust them. Ive done so many and never adjusted them that when I do a top end now, I never even check the valve clearances when I put it back together cause I've never had one need changed.

Flywheel puller is only special tool needed, the rest can be managed by a decent mechanic.

If you've done motors before, you will have no problem doing a 4 stroke top end. Yamaha also comes with a service manual (not the 2021s) so it walks you through step by step.

Good luck
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numbers
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numbers 10/19/2020 7:12pm
10/19/2020 7:12pm
MotoX85 wrote:
Its really not as bad as you think. Pretty much the same concept as the 2 stroke. The cams and crank are marked so its really...
Its really not as bad as you think. Pretty much the same concept as the 2 stroke.

The cams and crank are marked so its really easy to line up. ALWAYS replace the timing chain and tensioner when you do a top end, ALWAYS...... these are actually more important then the piston.

Since you own a Yamaha, you will probably never have to redo the valves and id be surprised if you even have to adjust them. Ive done so many and never adjusted them that when I do a top end now, I never even check the valve clearances when I put it back together cause I've never had one need changed.

Flywheel puller is only special tool needed, the rest can be managed by a decent mechanic.

If you've done motors before, you will have no problem doing a 4 stroke top end. Yamaha also comes with a service manual (not the 2021s) so it walks you through step by step.

Good luck
You ever check the clearance in your crank bearings. Side to side and end play. Asking for a friend.
FWYT
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FWYT 10/19/2020 8:49pm
10/19/2020 8:49pm
BTW, one area that you might find a pain in the ass (at least, I did!) is slipping the barrel
on while trying to hold all those rings in place. Get a wide ziptie and put it around the bottom
two rings. Then you just have to squeeze the top ring and once the barrel gets over that, it will
just push the zip tie down as it slips over the other rings.
2
bierbower105
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bierbower105 10/20/2020 4:06am
10/20/2020 4:06am
FWYT wrote:
BTW, one area that you might find a pain in the ass (at least, I did!) is slipping the barrel on while trying to hold all...
BTW, one area that you might find a pain in the ass (at least, I did!) is slipping the barrel
on while trying to hold all those rings in place. Get a wide ziptie and put it around the bottom
two rings. Then you just have to squeeze the top ring and once the barrel gets over that, it will
just push the zip tie down as it slips over the other rings.
Always love a good ziptie hack.
2
navalseabee
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navalseabee 10/20/2020 4:18am
10/20/2020 4:18am
YouTube University, Rockymountain ATV’s channel has excellent how to’s.
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