2007 YZ450 Top End Rebuild


15 replies to this topic
  • Nick280

Posted February 09, 2016 - 04:21 AM

#1

Firstly I'd like to say Hello, I'm new to the forum and this is my first post. I live in the North of England here in the UK and have found this site to be more relative to my bike so decided to join up.

 

 

I'm rebuilding the top end of my YZ450f which I have just bought. The bike came with no history of maintenance and the previous owner quite openly admitted he had no idea if anything had been done piston or vavle wise. He had changed the oil during his 6 month ownership and kept the air filter squeaky clean but apart from that, the bike ran so he rode it. I checked the valve clearances which showed them all in spec except the middle inlet which is 0.5mm so I thought I would strip the engine down to the bottom end to see what condition it is in, and to be fair, it all looks pretty good. I will be replacing the piston and rings along with the valves springs, seals and timing chain as I read these are relatively cheap parts and have been known to fail causing expensive damage. I will be changing the valves too if they look worn once If got them popped out. 

 

My question is, the conrod bearing onto the crank has quite a bit of movement in a rocking side to side way. I can feel nothing vertically and very little horizontally (well within tolerance), but if I rock the conrod at the little end, side to side in a pendulum type way, I have about 1.5-2mm movement at the little end. Is this acceptable and ok to leave?

 

Also, which piston do you guys recommend or should I just stick with the OEM parts?

 

Thanks in advance.

 

Nick

 

 



  • UncleLuke

Posted February 09, 2016 - 05:24 AM

#2

I will be replacing the piston and rings along with the valves springs, seals and timing chain as I read these are relatively cheap parts

 

 

My question is, the conrod bearing onto the crank has quite a bit of movement in a rocking side to side way. I can feel nothing vertically and very little horizontally (well within tolerance), but if I rock the conrod at the little end, side to side in a pendulum type way, I have about 1.5-2mm movement at the little end. Is this acceptable and ok to leave?

 

If the bike is clean and low hour you are probably wasting money throwing in new parts. I would just ride it, until parts fall out of spec or you get up to 200+ hours.

 

Timing chain, yes.

 

Rod limits are listed in the manual:

 

CRANK TO CONNECTING ROD CLEARANCE
0.15 ~ 0.45 mm (0.0059 ~ 0.0177 in)
0.50 mm (0.02 in) SERVICE LIMIT

Small end free play:
0.4 ~ 1.0 mm (0.016 ~ 0.039 in)
2.0 mm (0.08 in) SERVICE LIMIT

Runout limit on shafts:
0.03 mm (0.0012 in)
0.05 mm (0.002 in) SERVICE LIMIT

Crack width outside to outside of crank halves:
61.95 ~ 62.00 mm (2.439 ~ 2.441 in)


Edited by UncleLuke, February 09, 2016 - 05:28 AM.


  • Nick280

Posted February 09, 2016 - 06:34 AM

#3

If the bike is clean and low hour you are probably wasting money throwing in new parts. I would just ride it, until parts fall out of spec or you get up to 200+ hours.

 

Timing chain, yes.

 

Rod limits are listed in the manual:

 

CRANK TO CONNECTING ROD CLEARANCE
0.15 ~ 0.45 mm (0.0059 ~ 0.0177 in)
0.50 mm (0.02 in) SERVICE LIMIT

Small end free play:
0.4 ~ 1.0 mm (0.016 ~ 0.039 in)
2.0 mm (0.08 in) SERVICE LIMIT

Runout limit on shafts:
0.03 mm (0.0012 in)
0.05 mm (0.002 in) SERVICE LIMIT

Crack width outside to outside of crank halves:
61.95 ~ 62.00 mm (2.439 ~ 2.441 in)

 

Thanks for the reply. I have the tolerances from the manual but there isn't a one for the pendulum tolerance lol. I think it will be fine but wanted a second opinion, as if the upper lateral and lower lateral movements are within tolerance, the pendulum effect won't be able to occur and the conrod will run tru. 

 

The strip down started as cleaning the bike but bits kept coming off and I ended up stripping the engine down to do a top end rebuild. It's going to be a couple of weeks before the bike becomes road registered so may as well get the engine ready for the abuse the road will give it.



  • grayracer513

Posted February 09, 2016 - 08:09 AM

#4

It is important that you correctly analyze the rocking motion at the rod.  There are two forms of lateral movement to be measured, one is rod side clearance, "D" in the picture, and the other is labeled as "small end free play".  Side clearance is simply that, the clearance at the side of the rod.  The so called small end free play actually is used to indicate the clearance between the crank pin and the rod bearing by measuring the amount that the rod can be rocked side to side as a result of the clearance at the pin.  The measurement is made using a dial gauge at the top of the rod while rocking the rod on the crank pin BUT NOT letting it slide side to side on the crank pin while rocking. 

Attached Thumbnails

  • rod.png


  • Nick280

Posted February 09, 2016 - 08:18 AM

#5

It is important that you correctly analyze the rocking motion at the rod.  There are two forms of lateral movement to be measured, one is rod side clearance, "D" in the picture, and the other is labeled as "small end free play".  Side clearance is simply that, the clearance at the side of the rod.  The so called small end free play actually is used to indicate the clearance between the crank pin and the rod bearing by measuring the amount that the rod can be rocked side to side as a result of the clearance at the pin.  The measurement is made using a dial gauge at the top of the rod while rocking the rod on the crank pin BUT NOT letting it slide side to side on the crank pin while rocking. 

 

Ah! OK, I understand what you are saying. I will have another look tonight to check what I have while keeping the big end of the conrod from sliding.

 

Thanks for the clarity on that one :)



  • Treeyz450

Posted February 09, 2016 - 01:51 PM

#6

Firstly I'd like to say Hello, I'm new to the forum and this is my first post. I live in the North of England here in the UK and have found this site to be more relative to my bike so decided to join up.


I'm rebuilding the top end of my YZ450f which I have just bought. The bike came with no history of maintenance and the previous owner quite openly admitted he had no idea if anything had been done piston or vavle wise. He had changed the oil during his 6 month ownership and kept the air filter squeaky clean but apart from that, the bike ran so he rode it. I checked the valve clearances which showed them all in spec except the middle inlet which is 0.5mm so I thought I would strip the engine down to the bottom end to see what condition it is in, and to be fair, it all looks pretty good. I will be replacing the piston and rings along with the valves springs, seals and timing chain as I read these are relatively cheap parts and have been known to fail causing expensive damage. I will be changing the valves too if they look worn once If got them popped out.

My question is, the conrod bearing onto the crank has quite a bit of movement in a rocking side to side way. I can feel nothing vertically and very little horizontally (well within tolerance), but if I rock the conrod at the little end, side to side in a pendulum type way, I have about 1.5-2mm movement at the little end. Is this acceptable and ok to leave?

Also, which piston do you guys recommend or should I just stick with the OEM parts?

Thanks in advance.

Nick


I wouldn't chance it. I would get a new crank assembly from hot rods. I think I paid $270 ish for it shipped and ready to drop in. This is after I thought the tolerances were ok and it ended up locking up on me.
It's not too bad of a job at all.

Just my opinion tho

  • grayracer513

Posted February 09, 2016 - 02:08 PM

#7

I wouldn't chance it. I would get a new crank assembly from hot rods. I think I paid $270 ish for it shipped and ready to drop in. This is after I thought the tolerances were ok and it ended up locking up on me.
It's not too bad of a job at all.
 

 

As I recall, you have an '03, which model year had some degree of difficulty with wearing out and/or breaking the bearing cages on the big end, leading to the problem you had.  The rod and bearing were both revised since then, and the '07 does not run into problems like this with anywhere near the same frequency.

 

Regarding the OP's question on pistons, I prefer OEM unless I need higher than stock compression (almost never).  They're forged, just like aftermarket, and are as reliable as anything you can put money down on. 



  • Nick280

Posted February 09, 2016 - 02:15 PM

#8

OK, got the head stripped tonight, looks like a set of valves needed. Inlets are ridged/stepped and the exhaust valves are starting to show some wear. The seats look really good though and after cleaning the head up, it all looks pretty good. Valve stem oil seal are quite hard so they do need doing.

 

I checked the conrod again with Grayracers advice and with not allowing the conrod slide on the crank pin, the movement isn't that bad. I tried to gauge it but I couldn't get a good anchor for my dial gauge so gave up. I'll stick with the crank and rod as it is until next time and regauge (get it) the situation again then.

 

Timing chain looks a bit of a pig to do. Is that the case? Will I need a puller to get the whatever it is on the crank off (guess I should look in the manual rather than being lazy!!)?

 

I was going to ask about whether to get OEM or aftermarket parts again so thanks for adding that.

 

 

 

Cheers.



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  • grayracer513

Posted February 09, 2016 - 02:23 PM

#9

The timing chain is a piece of cake.  It's removable from under the left side crankcase cover after the flywheel is pulled.  You need to unbolt the lower end of the rear chain guide so you can slide it out of the way, but that's it.  Nothing comes off the crank; the gear is cut directly onto it.

 

http://www.thumperta...f/#entry2520291



  • Treeyz450

Posted February 09, 2016 - 05:31 PM

#10

As I recall, you have an '03, which model year had some degree of difficulty with wearing out and/or breaking the bearing cages on the big end, leading to the problem you had. The rod and bearing were both revised since then, and the '07 does not run into problems like this with anywhere near the same frequency.

Regarding the OP's question on pistons, I prefer OEM unless I need higher than stock compression (almost never). They're forged, just like aftermarket, and are as reliable as anything you can put money down on.

Mine is an 08.............

Come on gray, you can't remember everyone's ride???

  • grayracer513

Posted February 10, 2016 - 08:23 AM

#11

Now that most of my hair is gone, I can't keep as much on top of my head as I used to; too slippery. 

 

But, now that I'm here again, if you replace the crank, I personally would use only a new OEM crank assembly, or rebuilt with new Yamaha parts.  Hot Rods stuff is good, Yamaha's is better. 



  • Nick280

Posted February 12, 2016 - 02:37 PM

#12

OK, After much thinking (and alcohol) after seeing what titanium valves cost and the possible frequency of them needing changed, I'm debating as to whether to keep the original valves and seeing how long they will last. I cant decide, when the time comes, whether to fit stainless valves as these will last longer than titanium. I'm not riding the bike to win competitions, just to put a smile on my face and pop a few wheelies.

 

Here is a couple of photos of my cylinder

 

Barrel%202_zpsdfrzg7te.jpg

 

Barrel%201_zps3yiqn10p.jpg

 

To me the cylinder looks perfectly fine. Am I right to think this?

 

 

 

And here is what my exhaust valves look like (one photo as they both look very similar)

 

Exhaust_zpsxx7wjrbb.jpg

 

Again, to me this looks fine to reuse

 

 

 

And the inlet (again, all 3 look very similar)

 

Inlet_zpsmp70kw5l.jpg

 

These are the ones that are taking up much of my thinking RAM, I'm not sure if these will last very long. Whats your opinion???

 

 

I cant believe how little info and spares there are for the YZ450 here in the UK. Search for anything other than brake or oil related products and you end up in the US. I may have to move :lol:

 

Thanks in advance for telling they're fine and they will last forever (haha).

 

Serious though, thanks for any advise given.

 



  • grayracer513

Posted February 12, 2016 - 03:56 PM

#13

I would hone the cylinder using a silicon carbide "bottle brush" hone. 

 

The valves look usable.  Have either of the two you show ever had to be adjusted?  If not, I'd run them until they need their second size smaller shim (.10mm smaller than what they currently need.  No longer than that, though.

 

SS valves don't really last any longer than OEM titanium.  Plus they require heavier springs because of their extra weight, and the spring sets are so much more expensive than the originals that it usually makes up for the price difference.



  • Nick280

Posted February 13, 2016 - 01:46 PM

#14

Hi Gray,

The problem I have is I don't know anything about the history of the bike hence my uncertainty. I should maybe just stick 3 inlets valves in and stop over thinking the situation.

I'm planning to build up all the stuff needed to completely rebuild the engine ready for this time next year, including a full head rebuild, crank and possibly a big bore kit, so as long as it will see me through this summer and next winter (this isn't my main ride. I have an 1190 Adventure for the big mile summer rides) I'll be happy.

Cheers for your help mate.

Edited by Nick280, February 13, 2016 - 01:47 PM.


  • Nick280

Posted February 24, 2016 - 01:33 PM

#15

Well, after a new piston and rings, 3 inlet valves, a full set of valve springs, a new timing chain, all valves nicely shimmed and a few hours work, she's alive. Back together and with a new plug and some fresh fuel, she started with less than 20 seconds of kicking on a dry carb. I'm pleased with that. I just started her tonight for the first time after finally finishing the top end build and noticed the header glowing bright red in the dark. I have seen a thread about glowing headers which I will look for next and read but while I'm here, I thought I'd mention it. I noticed too that with a little blip, the engine held onto a few revs before it came back to idle. I had the carb stripped during the rebuild and I'm guessing this will be due to fuel not being entirely round the carb yet, like in the accelerator pump for example?

 

Thanks to those that have advised me in the above and also the knowledge across the site which I have found and used. I've only ran her for a few minutes to get the rads warm and check the oil pressure was there but it all seems good so far :D 

 

20160224_204249_zpstaucqdxe.jpg



  • Nick280

Posted February 24, 2016 - 02:09 PM

#16

OK, so the glowing header  is normal. That's good :D







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