Intake valve strangeness!

[Gizmo]

So the X1 brake pad replacement which has now evolved into a major top end rebuild has thrown up a number of curveballs!


The latest one is the inlet valves. I have a lot of carbon in the heads, too much for a 22K motor in my book, Stripped the heads down to clean them up and the inlet valve seats are shot to sh!t


Looks to be too badly pitted to clean up (going to attempt it again at lunchtime). I have never seen inlets in this condition. Exhaust valves look perfect.


Any guesses what has caused this to happen? There are clear signs that combustion gas has been feeding into the inlet port.


Pistons look fine. There are still witness marks form the original hone on the bore so its in good shape but it was burning a bit oil which I put down to the valve guide seals which I am upgrading.

 

[Foxster]

Re: Intake valve strangeness!

One common cause on Sportys is a leaking valve seal. Leads to carbon on the valve that chips away at the seat. Buell might be similar.

Umm - thinking about it, that would usually only lead to one valve being knackered, not both.

Could be reversion I suppose - exhaust gases getting blown back. You got a shorty after-market exhaust on it, Phil?

 

[Gizmo]

Re: Intake valve strangeness!

One common cause on Sportys is a leaking valve seal. Leads to carbon on the valve that chips away at the seat. Buell might be similar.

Umm - thinking about it, that would usually only lead to one valve being knackered, not both.

Could be reversion I suppose - exhaust gases getting blown back. You got a shorty after-market exhaust on it, Phil?

Stock exhaust.

Only the inlet seat is burned. There is a big build up of carbon on the back face of the valve. I was suspecting bad seals as it was burning oil.

 

[Fast Lane]

Re: Intake valve strangeness!

The latest one is the inlet valves.

the inlet valve seats are shot to sh!t

Is it the valves or the seats that are pitted?

Unfortunately pitted seats are common nowadays, I see it all the time. A combination of ethanol in the fuel and lean mixtures from the factory contributes to this I reckon. I've never worked on an X1 - are they 7mm valve stems and if so what colour are the stock stem seals? If they're 5/16 stems then they are probably the K line type seals which go brittle with time.

There are clear signs that combustion gas has been feeding into the inlet port.

This is more common than you would think. I have a vacuum tester which I use before and after seat and valve work. Stock seats and valves usually leak due to eccentricity, often 0.002" or more between the valve face and the mating 45 degree section on the seat. Even this seemingly small amount can cause leak down and combustion pressure loss. Guide bore wear follows which then wears the stem seal leading to oil consumption and carbon accumulation. What about the head breathers - are they vented into the intake tract?

 

[Gizmo]

Re: Intake valve strangeness!

The valve seat was pitted. Valve looks fine (well not bad)

The seals are odd. They are metal shrouded and the seal is inside. Not seen anything lke it befor. Its actualy hard to identify the seal face. There is no colour code as such. I will take a pic tomorrow. Valve guides seem good.

After about an hour i managed to get the seat cleaned up to what i think is an acceptable degree. I will strip the other head down and see if it has a the same condition.

The breather feeds from each head into the porta-potty air box. I have noticed oil in tbe airbox. Could be blow by but the bores and rings look good.

Poor old gal. She has done me proud over the past 14 years. Never let me down. Not even so much as a flat battery. She deserves some TLC.

 

[Fast Lane]

Re: Intake valve strangeness!

Valve guides seem good.

If the seals are knackered you'll often find that guide bore wear is the cause. Use a small bore gauge to check if they're parallel or worn at the top and bottom. You shouldn't feel any stem to bore movement in the intakes, the bore gauge will tell you.

After about an hour i managed to get the seat cleaned up to what i think is an acceptable degree.

You can't tell by looking. Send them to me and I'll test them for free. Forget petrol or solvent leak tests. They would give an accurate result if the sealing face had to seal against petrol or solvent but compressed gas ... Nooooo ...

The breather feeds from each head into the porta-potty air box. I have noticed oil in tbe airbox. Could be blow by but the bores and rings look good.

It doesn't come from leaky rings. This is a crap system from the factory and is a major factor in carbon build up on the valve and chamber surfaces. There is oil mist present continually in the crank case which is displaced on every downward stroke of the pistons, straight into the intake tract. You'll be doing yourself a big favour by venting to atmosphere in the rebuild.

 

[Ukkid76]

Re: Intake valve strangeness!

It doesn't come from leaky rings. This is a crap system from the factory and is a major factor in carbon build up on the valve and chamber surfaces. There is oil mist present continually in the crank case which is displaced on every downward stroke of the pistons, straight into the intake tract. You'll be doing yourself a big favour by venting to atmosphere in the rebuild.

Would that be the same with any engine? like my Road King for example?

 

[Gizmo]

Re: Intake valve strangeness!

The stems measure .309"


Having examined the seal more closely the lip at the top has become hard and there is some kind of inner lip but my guess is that they are shot.


I intend to keep the breather stock as I am keeping the bike completely original (apart from the corbin seat), which is getting increasingly difficult as OE parts are getting harder to find.




This is the seal..

 

[Fast Lane]

Re: Intake valve strangeness!

Would that be the same with any engine? like my Road King for example?

Yes Dave. As the TC's have no crank case venting, all of the displaced air is evacuated through the cam chest, up the pushrod tubes, through the umbrella and baffle system and then out of the breather holes on the inner upper corners of the cylinder heads. From here the factory set up (emission controls) is to run hoses from the backing plate directly into the intake air tract. I prefer to do away with this and vent the gases to atmosphere. There are many ways of doing this, most involving mounting rubber hoses and some kind of catch can for any residue to be collected in. My own bikes run breathers made by Doherty Machine, unfortunately now gone.

 

[Fast Lane]

Re: Intake valve strangeness!

The stems measure .309"

They're worn. The intake stem should measure 3.108" and the exhaust 3.106". Measure the guide bore as well to to get your clearance. Too much will cause leaking seals.

This is the seal..

Yes that's the K Line style seal which always go brittle. Drop me a PM with your details and I'll send you some of these ...

 

[Gizmo]

Re: Intake valve strangeness!

PM'd, thanks


I will get the valves out of the other head later. I will post up some pics if its the same as the front.

 

[Gizmo]

Re: Intake valve strangeness!

Rear cylinder inlet..... eek!

 

[Ukkid76]

Re: Intake valve strangeness!

Rear cylinder inlet..... eek!

This doesn't look brilliant, but I've seen much worse that continue to work fine!! how may miles has it done?

 

[Gizmo]

Re: Intake valve strangeness!

This doesn't look brilliant, but I've seen much worse that continue to work fine!! how may miles has it done?

22k (from memory) it has started to falter on the throttle a bit but apart from that, and the oil consumption, which it has always had, it was running OK. I was alerted to an issue when it seem to be building up too much oil in the air box. Not a massive issue but it was not right. Bores and rings look perfect.


When you consider that according to the factory it was poking out almost 100hp and 100 ftlbs of torque from a 1200cc sportster motor It must be stressing a bit.

 

[Fast Lane]

Re: Intake valve strangeness!

This doesn't look brilliant, but I've seen much worse that continue to work fine!!

It will continue to work but there will be a noticable reduction in throttle response. Here are a couple of flow charts directly related to this topic for anybody that's interested. These heads are off of my Heritage, they are Screamin Eagle MCR heads that I had run for about 11,000 miles. I actually felt that the performance had deteriorated so I pulled the heads for a look. Both of the intake valve stem seals had hardened and were leaking with valves contaminated to about the same degree as Gizmo's. The X axis is the valve lift in inches and the Y axis is the corresponding air flow in cubic feet per minute. These heads are biased on the exhaust side anyway due to the port dimensions and valve size but just look how much less they are flowing on the intake on the first chart due to the carbon deposits on the valves. The first chart is as they came off of the bike (as they were from the factory) and the second is after I cleaned up the intake valves and did some minor port work. It was a completely different bike once the heads were back on ...