continuous valve sealing problems

bergbro · Aug 10, 2011

So the next question continuing down the "seat moving in the head" line of thinking is why is it the area closest to the headers that seems to move (and that statement based on wot I have seen in other unicam heads not Bergs) ie furtherest away from spark plug.
My guess (and thats all it is) is its something to do with the heat around the exhaust port softening the alloy? (seems too simple) but that seemsto be where older british castings have failed as well as the rice burners.
I take Taffys point about if you beat anything long and hard enough it will move, but why only one side (and all I have seen have been the same side) of the seat moves? (this could be where bushy is a few steps ahead already with the uneven loading applied by rocker insinuation).
This must warrent more discussion..... more beer required (now thats one thing you cant do on the www.... buy a round for the boys!)

Ironic how so many english speaking people can get a different interpretation of the same statement.
The world be a many wonderful place.

Taffy · Aug 11, 2011

It has nothing to do with DOHC or SOHC. it's to do with the way they put the seats in.

I thought you were all going to pull me up for not noticing for the first two years of business!

I just altered my technique and discovered the problem in the middle of last year.

So having "gone round Will's house" with this subject I think we're more or less back to my opening statement. I trust a few more of the 'homebuilders' will have a look and we'll get some reports back. even if a few don't confirm with my results at the beginning I won't be swayed. If I could overlook this with my experience then I'm sure that 'it looks ok to me' is to be expected.

regards

Taffy

DuaneB · Aug 11, 2011

I've just finished building up a spare head complete. I will likely swap them in the next month because I don't know the condition of the head that's on the engine now and I'd like to avoid any potential carnage. I will make sure to check the "contact patch" and report back.

Taffy · Aug 11, 2011

sorry to be pedantic but....

you can't have a catastrophy with this. It might be that the bike backfires or is a pig to start or pops on the overrun.

regards

Taffy

bergbro · Aug 11, 2011

Righto then.... just to summerise Taffy,
you are saying the seats are fitted out of true rather than wearing/shifting Yeah?
Its cetainly not every head that is like this so maybe its just monday and friday bikes?

Are seats fitted by machine in the factory or by an engineer? (he would be a busy man somedays). just wondering if its a machine set up issue or a tired technition. There are some scary storys out there about production variences from the 80's, but that is another thread.

Taffy, by approx how much out of true are they? Is it just a light lick with a seat grinder?

bushmechanic · Aug 11, 2011

like I wrote earlier its nuffink to do with the poor lil seats, look at the distribution of the alloy underneath the seat (SOHC vs DOHC) and also the action of the rocker arm. the valves move in the guide even when they are new.

then all is left then is for us to argue if its "normal" wear of the "distorted" seat / guide and valve at operating temp in a torqued down head or magic one sided hammering and creep. doesn't really matter. all you can do is install new valve guides, properly hone them and re cut the seats.

FWIW bergbro the unicam heads with problems I've seen all have the intake seats cut off centre to the guides.

spanner · Aug 11, 2011

Yes a worn valve guide ( although some of us refuse that possibility :roll: ) will allow the valve to move sideways especially when operated with a rocker arm. This sideways movement on opening and closing will wear a seat
unevenly.

Re-cutting a valve seat with a worn guide is just Jerry mechanics :lol:

6.05mm is the max Dia for the valve guide.

Cheers spanner

bergbro · Aug 11, 2011

Righto Aussies.... I am not disputing anybodies input on this thread, just trying to mediate an understandable explanation as these discussions in the past hav turnd not so helpful to the not so mechanically minded on this site.
I think we are getting somewhere...

Bushy, your saying its just normal wear an tear and thats the way they wear, but what I dont get is why its only some heads that seem to display this issue. Is it due to the way those motors are treated through their lives maybe?
Any idea why the unicam seats were cut off centre? (from the factory?)
Funny how ti valves beat hard seats up... but then rubber seals wear grooves into hardend steel so not unreasonable at all.

Spanner, I was going to suggest the return action of the valve to seat would not be under distorted load from the lever (rocker) therefore not have an uneven load on the seat, but thinking further.... its blimin hard to see whats goin on when it all happens 60-70 times every second under durress, therefore there will be unequal loads on the seat.

I hope I have not annoyed or ailienated anyone over this... thats not my intention.... gaining from others experiance and knowledge is all I am trying to achieve.

Hmmmmmm. I gota start drinking an stop thinking.

bushmechanic · Aug 12, 2011

not really "normal" wear perhaps abnormal wear under operating conditions is closer, still a stretch but its more plausible than one side of the seat being hammered so much it moves the alloy under it. if the head distorts under operating conditions though then it could be both.

if someone has replaced or removed the guides even for something as simple as to do a port job then the seats need to be recut once the guides are back in.

whatever the reason its a common problem in engines and mute point in the end because there's nothing you can do except start again; guide, valve, seat and giddyup

the uni-cam heads bro I reckon are CNC machined and then the valve seats are cut on the same machine without centering on the ID of the valve guides, it sounds dodgy I know but there are so many intakes up to 0.1mm off from the chonda factory that its really the only explanation that makes sense.

Taffy · Aug 12, 2011

I think I originally mentioned - maybe not - that it's mainly the earlier heads from 2001 - 2003. they had vicious cams in them with the '01', the '53' and the '55'. you can get a a kind of percussion shock I would imagine that could move material. but then I have to dismiss that because once one side has sunk then the other side should take all the load and sink to join it? but it doesn't?

I said mainly exhaust seats because the exhaust seats don't tulip so the valves and seats aren't moulding to each other as they are beaten. so the exhausts are a lot clearer. The inlets do have the problem which is always disguised by tuliped seats and valves.

I've only sold about 10 guides and they've been to racers that wanted to port and then start with a new head. so there must be a shed load of customers and bike shops who don't realise how worn out their bikes are.....

at the end of the day, the alloy of the head moving away is the only plausable answer. I don't have time to stop 'n' stare but maybe I will in the future....see if the seats have moved relative to the head etc.

regards

Taffy

DuaneB · Aug 12, 2011

Hey Taff... I wasn't suggesting that this misalignment would cause me any catastrophic problems... it was the fact that the head hasn't been off this bike for years, and I've never had it off since I bought the machine and I don't know what condition the valves are in... but I have tightened the valves back within spec several times so the valves may be ready to pull right through the seats by this time!!

Taffy · Aug 12, 2011

8O 8O :lol: :lol: :lol:

continuous valve sealing problems

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