Riddle me this: Intake valves way out of spec
 

Long story short, my bike's not starting, and hasn't been for some time now.

I chased down all electrical and fuel issues that I can think of, and aside from shocking myself a couple of times checking for spark plug gap, all seems well.

What happened was that the bike progressively had a harder and harder time starting over a few days (last time it started I had to bump it with a buddy), and then wouldn't catch. But once running it seemed fine. So in my head I ruled out a lot of issues that I maybe shouldn't have.

Finally got to checking compression, and it's very low in both cylinders (like 40 psi). Weird that it was in both, but OK. Should have checked crankshaft bolt b/c it was very easy to turn (also suggesting low compression). OK. Check valves... all four exhaust are in spec, all four intake have no measurable lash. I can't fit my smallest feeler gauge in there. What would cause all four to do this? It's so weird, I'm thinking I'll have to pull the heads but this one has got me :confused:

p.s.: I just had both heads rebuilt with new valves/seals about 6k miles ago as part of my project, could they have just seated so much that I need to shim them correctly?

No that is not normal.

Check the cams for wear first and if they are in spec then you should pull a head to find out what is going on.

Compression below 120 PSI is not very healthy pressure.
40 PSI in both cylinders??? What are the odds this will happen....
The valves could have not seated that much, something else is going on.
Check the timing first

Or an incorrectly timed camshaft... Could have the same effect as CCT's and flatten/mushroom the intakes...

I wonder if I messed up timing somehow swapping to the lighter flywheel.

It seems to be the same issue in both cylinders, which had me chasing ghost problems for a little bit. I'll pull a head this weekend after checking the cams.

All year VTR1000F flywheels are the same part number (something I checked) they all have the same keyway (I check each one against a known standard) and all a incorrectly timed flywheel would do is screw up the ignition timing. In no way can the flywheel effect the crank/cam timing.

If the cams are mis-timed causing a valve crash,, it had nothing to do with the install of the flywheel.

Leak down test would be what i would do prior to teardown.

Once you confirm your leaking past the valves, pull the heads and inspect the valve face, valve seat for wear, and the valve tip. Measure each valve shim with a micrometer. As suggested, check the cams for wear, both the lobe face, and the head / cam bearing journal.

Yeah good point, I'll do a leakdown first. I suspect it'll tell me what I already seem to have found out, that the compression loss is in the head/valves.

Good to know about timing, I couldn't think of where it would be off. When doing valves, the cams seem to be timed correctly. At least I have something to chase now, it was really unmotivating when I couldn't find anything wrong with electrical/airbox/carbs! I'd just stand in the garage, look at it for a second, then go work on something else...

Definitely re-check the intake cam timing when you take it apart, before you go all the way and remove the heads.

Who did the work? Did you put it together after a shop reworked the heads or did the shop do all the assembly? If the seats weren't lapped then the valves may have seated enough to erase all the lash that was correct before it was started the first time.

Local mechanic/shop did it (all I did was check the tolerances when he was done), I didn't and don't have a spring compressor. I was kinda thinking something along this... it seems like a problem that slowly appeared (and not one that happened instantaneously like jumped timing), so something like this would make sense... Maybe I'll buy a shim kit and play with it before taking off the heads. If I get compression back up to 150 or so I'll use that as an explanation ;)

If the pistons hit the valves, it would bend the stems, preventing the valves from closing, which would cause the valve clearance to increase.

Are you checking clearance on the base circle of the cams?

Yes I believe I'm checking clearances correctly. I've checked them a few times on bikes and on my truck, and the exhaust are all reading in spec so it seems it would be something more like what VTRsurfer is saying.. not sure why... probably have time tomorrow to pull the head but I may wait and try to shim them and see how that goes.

sounds like bent valves.
or the seats were cut to large and the valves got sucked up in the seats.
no compression means the valves arent sealing.
getting the clearance correct will not fix this,there is something wrong with the service performed.

Umm, I dont think it does..

NO clearance is not indicative of bent valves, just the opposite.

Bent valves have a tell tail sign of LARGE clearance. The Bent valve does not seat fully... that leaves a gap at the valve tip.. ie huge clearance.

Low compression and No clearance, after a valve job and a previously well running initial use points more to the valve face wearing and the valve receding into the head... or less likely the valve seat wearing.

I see new valves do this when folks mistakenly lap coated valves, with the few microns thick coating is worn off (from lapping) the vale seats and seals very well during initial use, but wears rapid;y and goes to zero clearance, no longer seating / sealing and you have compression loss.

7moore7, did the shop only replaced the intake valves?
I find it a bit odd that it happen only to the intake valves...

did you read my complete post?

or the seats were cut to large and the valves got sucked up in the seats.
no compression means the valves arent sealing.
getting the clearance correct will not fix this,there is something wrong with the service performed

Yes sir i read the part I thought was incorrect and replied to it, I read the part I agreed with and continued that train of thought.

Not really sure what you mean by "seats were cut to large and the valves got sucked up in the seats"

Have you ever cut or ground valve seats? Installed valves? (that's a question so I understand where your coming from with your ideas, not a flame or slight in any way)

If the seats were cut to large and the valve seated to deep, it would have been noticed when assembled, and when the end user set the valve clearance.

If you mean the seat was cut a a grossly wrong angle, or set of angles and the valve face wore quickly to conform to that wrong set of seat angles .. :iagree:

That or the face of the valve was cut wrong, coated valves cut or lapped.

Am I completely off in thinking the intake cam could be misaligned? Like off a tooth so its opening them at the wrong time? Is this a nuts idea?

no i havent,but i understand the teory.


this is what i was thinking.
If you mean the seat was cut a a grossly wrong angle, or set of angles and the valve face wore quickly to conform to that wrong set of seat angles ..

wouldnt hurt too check.

one tooth off of true TDC would still have the cam on the base circle, not on the lobe ramp..as well as the user described and stated he was checking clearance with the cam / bucket off the lobe.

And the other thing is, it ran well at first.. Installed fine, clearance fine, THEN later, stopped running, and he found intake clearance at zero (or below)

Not sure the cams could be miss timed enough to have a valve open (low or no compression) and not bend the valves. Never tried it :) The engine is of course an interference design and has little room for error in cam timing before valves hit the piston.

Absolutely :iagree: if for no other reason then to rule it out as part of the diagnostic process.

I guess its easy to fall into the diagnostic trap of thinking the exact same thing CANT be wrong with 2 heads at the same time but actually it could (and seemlingly is). Maybe something wrong with the recent adjustment?

Have you tried another compression tester?

Hey guys been away for a day, I'll throw in some more info here to help rule out possibilities. It doesn't help that I can't verify a lot of this due to other more pressing projects, but hopefully will get some time tomorrow and definitely will this next week.

Marquez seems to be understanding: I had all 8 valves/seals replaced due to poor seating/carbon buildup (low compression diagnosed this) about 6k miles ago. When getting the heads back from the shop, I did a compression test and they were at 150/154 psi. And the bike ran great. So timing is unlikely... especially since it's two chains... and I've manual cct's so no skipping involved.

The bike seemed to run decently when it decided it didn't want to start anymore, so that threw my diagnosis off for a long time. As in, if it was running fine, but wouldn't start, it had to be electrical or fuel...

BUT it could have progressively been running worse and I didn't notice, especially since I was commuting in it so not really wringing it out at all...

So, we have low compression and all intakes are reading with zero lash (so probably not bent). I'll do a leakdown compression test, maybe try to find another gauge as suggested (this one's been through a garage move), but evidence points to the valves already. I just was confused as to what/why this could happen.

Marquez, when this happens:
- what usually ends up being the fix? Can you re-shim them or will they keep wearing and I'll need new valves? They were Honda OEM and I just handed them over to the shop so I don't know if they were lapped or not.

They keep wearing.. BUT that is on coated valves that have had the coating removed or compromised,,, plain stainless steel, it's not an issue.

Marquez is on the right track. It'd definitely the valves. Most likely the faces of the valves dishing. Possibly the seats but I'd bet it's the valves. They dish out and recess into the head. Just to double check roll the cam loab so it's pointing straight up from the valve not at TDC. This will gurantee it's not on the clearance ramp though I'm sure it's going to show the same results.

It's definitely not the cam wearing as that'd result in excessive clearance. Not going to be cam timing either as it ran fine before.

I'd adjust the clearance and see what happens. It'd most likely run and start great again. But see if the clearance continues to go away. It could be the valves seating in but I doubt it. I'm guessing as Harquez is saying the valves got lapped taking the stelite coating off and now is wearing into the softer metal underneith. The only real fix if this is the case is to replace the valves.

Is the shop that did the work a bike shop or an automotive machine shop? Either way I'd go back and ask them if they lapped the valves and if they say yes let them know what's going on and ask them to buy and replace the new valves.

It was a motorcycle shop (well, just one guy, so he'll know if he lapped them or not for sure). I haven't talked to him in over a year though... been doing everything myself. Just got my cam kit in today so hopefully I'll get a running compression check.

Well I still stand by my first reply. I would start with the cams, is it likely, no but for no other reason then to rule it out as part of the diagnostic process.

Also wear can be other things than parts just getting smaller, galling is just one example of what I am talking about.

After that I would pull the heads, not mess around with re-shimming.

Look at it this way, the average valve "wear" on these bikes is maybe .001" in 20-30K miles.

On your bike they have moved approx. .007" in 6K miles.

So you can pull it down and fix it now, or re-shim and fix it later after you have done more damage.

Mike- I'll measure the cams tomorrow. I got it re-shimmed and buttoned up but am positive I have it 180 out when I play it back it my head so I have to pull at least the front cover off again.

What you're saying definitely makes sense...

Do you think I could do more damage by shimming and seeing what happens? My two reasons for this are 1) To make sure this is what what was causing my bike not to start. 2) I'm going to have to do emissions in March and having a running bike is the only way to do that.

I realize it's the easy way out just shimming, but I'd just a soon do a motor swap as I would pull the heads again, haha!