Checking a Crank for Endplay/rod clearance

[Brawg]

I am back into my 08 YZ450 after it ingested a ton of dust at the last 2 harescrambles. I'm already in it for a new cylinder, piston, rings and more than likely valves. The reason I am asking about the crank is due to my guidance from the local Yamaha "stealership". With the dust ingestion came running hot and the kickstart side intake valve hitting the piston ONCE! I attribute the valve smacking the piston to piston/cylinder wear and/or a stuck intake valve. My thinking is that when the engine ran hot, the valve springs weakened allowing that valve to "float". The cam journals did not seize, or even begin to seize.

SO, for the direct question...How do i check the crank and what is the spec that i'm checking against? I'd love to throw another $1500 at it for a complete rebuild, but it's just not in the cards this go round.

This is an OEM crank that was replaced last winter...9-10 races on the entirely new rebuild and now this.

What do the wise have?

[grayracer513]

Look at the diagram on page 2-6 of the manual (or 4-57).

The main bearing on the drive side (right side) of the crank controls crank end play. If either main shows more than .001" vertical play or .004" end play when cleaned and dried, replace it. If the drive gear is not torqued up, the crank can slide in the bearing. Don't measure that.

The rod bearing is checked first for side clearance, the clearance the rod has between the crank halves. Slide the rod all the way to one side, and gauge the clearance on the other.

Clearance between the crank pin, rod bearing and rod race is measured by rocking the rod on the crank pin without letting the big end slide either direction along the pin as you do so. Greater clearance at the rod bearing will allow the rod to tilt more, as it is much easier to measure this way than by trying to move the rod up and down on the pin.

[Brawg]

Gray,

So....with the crank still in the cases i need to guage the clearance between the rod and the crank half opposite the way I have it slid on the pin, right? That will give me a measurement for the wear of the actual ball type crank bearings?

To guage the wear of the rod needle bearing, measure the total play at the piston end of the connecting rod in a side to side manner?

I'm fairly certain that i understand both of these measurements. Now for their respective implications. I do not feel that the crank has significant wear based mostly on the fact that it's a OEM Yamaha crank, it's not seen that much time, i run Motul 300v, change it every race and keep a new and clean air filter on it all the time. "IF" there was enough play in the rod to cause the piston to hit an intake valve, wouldnt ALL of the intake valves hit the piston...not just one? I will check the clearances as defined above for peace of mind. Would you mind expanding on the hypothetical scenarios that would cause ONE intake valve to hit the piston?

1) Valve stuck

2) Crank is going out causing over extension on the exhaust and compression strokes

3) Jumped time/broke or seized cam/cam chain...(did not happen)

4) Valve spring weakened by heat (ran hot) and floated the valve

5) some other reasonably logical explanation for this occurance????

Thanks,

Josh

[grayracer513]

So....with the crank still in the cases i need to guage the clearance between the rod and the crank half opposite the way I have it slid on the pin, right? That will give me a measurement for the wear of the actual ball type crank bearings?

No. That will give you the rod side clearance. Clearance in the main bearings has to be checked with a dial indicator at the end of the crank.

To guage the wear of the rod needle bearing, measure the total play at the piston end of the connecting rod in a side to side manner?

You rock the top of the rod without letting the big end slide back and forth on the crank pin. The looser the bearing, the more it will rock.

"IF" there was enough play in the rod to cause the piston to hit an intake valve, wouldnt ALL of the intake valves hit the piston...not just one?

Maybe.

Would you mind expanding on the hypothetical scenarios that would cause ONE intake valve to hit the piston?

1) Valve stuck

2) Crank is going out causing over extension on the exhaust and compression strokes

3) Jumped time/broke or seized cam/cam chain...(did not happen)

4) Valve spring weakened by heat (ran hot) and floated the valve

5) some other reasonably logical explanation for this occurance????

Thanks,

Josh

Most likely is a valve that stuck or a chunk of carbon that dislodged and got caught between the valve and seat, but it could have been a weak spring. The thing is that springs don't loose tension from heat or most other reasons and recover from it. You should consider a new set for the $45 or so they will cost you. Just cheap insurance.

[Brawg]

10-4 on the springs...i'm probably just gonna replace all of the valves and springs. Would you say that i need to replace the guides? What about cutting the seats? OEM springs and valves will be about $300. If the crank checks out, which it should, then the whole top end and valve train will be new minus the cams. I plan on milling the head in order to remove the .002" warpage that i have guaged thus far.

Any other suggestions Gray?

Thanks a million, or at least $300! ha

[grayracer513]

The guides in a YZF wear very little, but they are critical to the longevity of the valve. A good machinist should evaluate them.

If you replace a valve, you MUST have the seats refinished. Otherwise, you're putting a valve with a flat, concentric face down on a seat that isn't either one, and it will have no chance of lasting. NEVER lap Ti valves.

[Brawg]

I know that i shouldnt lap the valves, but that is for the sake of the valves, not the seats...right? With that being said, would using an old/straight not worn out valve suffice for lapping the seats? Will lapping the seats stand in the place of "cutting" the seats or are you referring one in the same?

[grayracer513]

No. Only in the case of a valve seat that had no real wear on it in the first place would something like that work, and then only if a new steel valve were used to lap the seat.

There's no shortcut.

[Brawg]

Gray,

Just got the head back fromt the machine shop. Got the valves faced and the seats cut. (the yamaha manual says to "reface" the valves" and the machinist says it was ok to do. I also "block ground" the head to remove about .002" of warpage. I put the valves back in and shimmed to the appropriate clearances. For posting info sake, i'll give shims used. The stock shims were intake "I" and exhaust "E"

Stock shims-

I-.185mm

E-.175mm

After seats cut/Valves faced

I-1.65/1.68

E-1.60/1.60

This coincides with the intake valves leaking the most and/or having to be cut deeper to get straight. After machine work was done, the head and valve train held 24 inches of vaccuum. The springs tested within spec given by Yamaha manual. I paid $97 for the machine work for infor purposes.

I also bought another new head gasket and bolted it all down today. I was in a hurry, but i'm comfortable with the process after having it off about 20x's. I do not have a compression tester to fit the YZ spark hole, but with all new parts ie: cylinder, piston, rings, valves, gaskets, etc...i find it hard to believe it could be low on compression.

I have fire at the plug when not installed but it wont hit a lick!

I have the cams timed as shown in the manual. To describe how they are timed I would say the intake has one dot level with the head on 3 oclock and one at 12 oclock. The exhaust cam has one dot level with the head at 9 oclock and 1 at 12oclock. This puts the cam lobe position at TDC pointing up, away from each other at approximately 10 oclock and 2 oclock.

Why wont it start?

[grayracer513]

Probably fuel. If the bike has been sitting for any length of time, it is possible that either the gas went bad, or the pilot jet developed a film of varnish in or over the orifice or one of the cross holes, or the passage around the tip of the pilot screw that's blocking it at least partially. The pilot is only around .012-.016" inch through the metering orifice, so a tin film of varnish will cut that in half quite easily.

A third possibility is that either the float hinge is stuck, or the needle is stuck to the seat, shutting off the fuel to the carb.

BTW, OEM valve springs are about $40 a set. I always just replace them.

[Brawg]

I will check that...but I dont think its fuel. The crank/cam timing is what i have my eye on. I'm just boggled about it at present. I have it timed as the manual says and as described above, but i think i'm half a stroke off. My dad is an ace so we are gonna look at it tomorrow or friday. I will clean the carb either way. I will also post what I had wrong.

Thanks Gray, have a good thanksgiving.

[Geoffit]

,

"Just got the head back fromt the machine shop. Got the valves faced and the seats cut. (the yamaha manual says to "reface" the valves" and the machinist says it was ok to do. "

You say the valves are faced? if you are using new yamaha parts that's not going to be good in the long run, keep an eye on your clearances and don't go back to that shop....?

[grayracer513]

Titanium valves cannot be refaced. Hopefully, any competent machine shop would know that. The seats must always be refaced when replacing valves.

[tech24]

I had my '04 vavles done too even though I asked for them to be replaced and got the head back 4 days later with refaced valves and machine shop said it was ok too. Haven't had the bike running since so don't know what the wear will be like but stuff isn't going back there. Just thought I'd add!

[YamaJet]

Out of curiosity, what type of machine shops are refacing ti valves. Are they automotive centered shops? They may be totaly unaware of special handling for ti valves since automotive and most older tech bikes use steel valves which can be faced and or lapped within limits since there is no coating to worry about.

Just asking.

[grayracer513]

Titanium valves cannot be refaced or ground as steel valves can in any way. They have to be replaced. The seats can be resurfaced, and the best choice is a shop specializing in and experienced with modern motorcycle heads. Hand cutters are "OK", but the best is the serious 5 axis seat cutters the big shops are using.

[YamaJet]

Titanium valves cannot be refaced or ground as steel valves can in any way. They have to be replaced. The seats can be resurfaced, and the best choice is a shop specializing in and experienced with modern motorcycle heads. Hand cutters are "OK", but the best is the serious 5 axis seat cutters the big shops are using.

I guess thats what I'm saying. TI valves can't be ground or faced like steel so dont take your bike heads down to the local NAPA machine shop where valve facing is the norm for automotive or steel valve bikes.

Edited December 6, 2010 by YamaJet
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[tech24]

Out of curiosity, what type of machine shops are refacing ti valves. Are they automotive centered shops? They may be totaly unaware of special handling for ti valves since automotive and most older tech bikes use steel valves which can be faced and or lapped within limits since there is no coating to worry about.

Just asking.

Sent mine to a very reputable bike/quad race shop but wont be going there again

[grayracer513]

Sent mine to a very reputable bike/quad race shop but wont be going there again

Without naming names, explain why not.

[tech24]

Without naming names, explain why not.

I clearly stated on the phone to replace valves and even zip tied a note card on the head that stated the same. I get it back a week later with a valve job receipt. I asked the owner if it was ok to grind my titanium vlaves and he said yes and they do it all the time on oversized valve applications. I think I posted his reponse on here somewhere. Everyone I know deals with them for quad drag racing engines and all with good results but I just didn't get what I asked for.

We talked about in a thread and decided to run the head the way it was and see what the results were but I ran out of money and still haven't finished the engine or the rest of the project for that matter. You may remember, it was a while ago but going by the '04 service manual I lapped my valves to clean up some cruddy faces while I had it apart not knowing they were titanium.