continuous valve sealing problems

Just thought I'd drop a line to tell you about the valve sealing troubles I seem to be getting when rebuilding engines.

I often didn't used to have to worry about valves sealing on the exhaust side but in recent engines it has been virtually every single one!

lapping the valves in, I find that the valve seal is ground 360 degrees a nice dull gray but the seats always have 180 degrees unused. I get the seats done with a single angle cut (traditional).

I have on 1 in 4 engines discovered the same with the inlets, not so bad. the inlets have other issues such as "tuliping" but I've also noticed that people have changed the valves and not cut the seats. this means the valve is sealing on the tinniest of edge rims and that the valves are even more certain to tulip next time as they are being held even further out and on less material!

so I've been getting the inlet seats done as well. I used to get them 3 angle cut but now I leave them to a single cut and go for the broader seat to support the inner (thicker and stronger) part of the valve's sealing ring.

On all rebuilds I go around with a rotary file and open the combustion chamber where it 'shrouds' the inlet valves.

this could be why a few machines are backfiring in the exhaust or popping back in the carb?

the seats always sink over the ports which is just so typical of the ducati 2-valvers. there is plenty of support so I don't know what has gone wrong.

just to be clear: the exhaust seats slip and the inlets tulip with the rare and occasional slip.

regards

Taffy

Taffy said:

lapping the valves in, I find that the valve seal is ground 360 degrees a nice dull gray but the seats always have 180 degrees unused. Taffy

Click to expand...

hey taffy,
in the old days, i would hand lap valves to read the pattern of the 'valve to seat' relationship.
i would do this put putting some lapping compound on the valve and then lap [spinning the valve on the seat using a hand held tool that attachs to the valve face. obviously the valve spring is off.] the valve on the seat.

if this is what you are doing and the valve shows full contact but the seat does not then i would guess the seat is not exactly perpendicular to the valve guide. if you get a bad knurl on the guides that can be a problem.
anyway what i'm trying to say is that the only thing i know of that wold cause this is an error in the relationship of the guide to seat.
if the problem isnt too severe, you can lap it away but that takes alot of work. you may be able to use 'plasti-gauge' to measure the error by placing the pg in line with the airflow flow and installing the spring. but this will just tell you how bad the bad is.
also, i hope you can make it to fr4.
your brother from another mother.
tuts :devil:

tuts said:

your brother from another mother.
tuts :devil:

Click to expand...

:twisted: :twisted: :twisted:

yeh but still a fatherless MF! :lol: :lol:

I'm doing it exactly as you say Tuts but I say that it is give over the ports that is doing it yet the look absolutely 100% solid and three times the material that the Ducati's had. but it is always over the ports that it happens.

regards

Taffy

Taffy said:

but I say that it is give over the ports that is doing it yet the look absolutely 100% solid and three times the material that the Ducati's had. but it is always over the ports that it happens.

Click to expand...

taffy, not sure what you mean by 'give over'.
sorry i only know ingklish.

a bent valve will lap all the seat but only part of the valve.
you cant bend a seat so it has to be the valve isnt 90 degrees to the seat and the valve angle is controlled by the valve guide bore [if there is a valve guide, that is maybe its intergral to the head and not separate? not sure but it doenst matter].

I've said pretty much what you said in the post above. I'm getting 100% contact with the valve and only 50% at the seat. cut the valve seats and then I get 100% contact.

the exhaust valves are easy to spot, they have no shiny steel contact area through the carbon - just black.

I meant "giving way" the seats are giving way over the port areas.

regards

Taffy

http://www.youtube.com/watch?v=ysc_tux- ... r_embedded

Only way to have it done IMO

are we disagreeing here somewhere spanner?

regards

Taffy

I would question the seat installation. Time to try another machine shop.

I'm not putting any seats in!!!!!! (yes I'm shouting it!)

these are the factory seats, factory valves and they are tipping.

OK, so nobody believes me or can get their head around it.....

the reason nobody has said it before is IMHO because it is subtle, it is delicate, you have to be taking your time and be diligent. I'm all of those and I thank you for your time!

regards

Taffy

Taffy said:

I'm not putting any seats in!!!!!! (yes I'm shouting it!)

these are the factory seats, factory valves and they are tipping.

OK, so nobody believes me or can get their head around it.....

the reason nobody has said it before is IMHO because it is subtle, it is delicate, you have to be taking your time and be diligent. I'm all of those and I thank you for your time!

regards

Taffy

Click to expand...

Well then....I'm thinking maybe you should be replacing the seats then I understand that you feel that there is a possibility of the casting design causing an issue with the seats deforming. It is more likely that the seats just need to be replaced. I know the older bikes (pre 01) had seat durability issues. Just my 2 pence

I can tell when seats have been cut so I'll keep an eye out. I'd take a photo but it just doesn't show up.

put it this way:
three heads
all 4
2 exhaust
all four

and previous to them always the tuliped inlets or tipped exhaust seats.

let's see what happens with the next one.

regards

Taffy

Maybe the heads are soft

nuffink to do with the seats

clue for ya taff

doesn't happen as often on DOHC :wink:

Arrr so Taffy is not replacing the valve guides when he does a head job?
The guides don`t seem to last very long I have noticed.

spanner said:

Arrr so Taffy is not replacing the valve guides when he does a head job?
The guides don`t seem to last very long I have noticed.

Click to expand...

what??????????

the guides and seals are positively the best thing about a husaberg after the gearbox. there's no wear on them and I've only ever looked to change one set of guides since I started.

guides have got nothing to do with this.

come on spanner.

regards

Taffy

I beg to disagree replaced mine at 5000 km completely shagged

Head is off at the moment at 7500 km and it wont be going back on without
replacing them again, + valve job.

I think I see where Bushie is coming from :wink:

Cheers spanner

spanner said:

I beg to disagree replaced mine at 5000 km completely shagged

Head is off at the moment at 7500 km and it wont be going back on without
replacing them again, + valve job.

I think I see where Bushie is coming from :wink:

Cheers spanner

Click to expand...

yes but who else talks about guides here? who else needs them? have you ever thought it might be you that's a little bit different?

regards

Taffy

So to sumerise..... and please correct me if im rong
Taffy sez the seat must b moving in the head. (due to heat maybe? or soft materialunder the seat?)
Spanner sez the guides wear quickly (inferring the worn guide allows the valve to beat the seat in or to move off centre far enough to not contact the seat squarly?)
Bushy is hinting at the rocker pushing the valve offcentre (and generating excess guide wear or guide movement?)

Personally I have seen other unicam motors (I mainly deal with single cylinders) also have simalar symptoms to what Taffy has described. Seems to be motors that have been neglected and thrashed to a stop (not properly serviced from new, or in one case never even had the oil changed from delivery, but that whole motor went in the bin) from the limited number of cases I have seen. (not infering anything to anyone, just stating my observations from limited experiance)

Not sure I understand why the valve seat would not lap in squarly with a worn guide as I would have thought the valve would only move off centre when under pressure from rocker?

Please enlighten my ignorance someone......

well as I say, the valves don't lap in with the poppet stick and then after having them cut they lap in perfectly so it is the seat.

quite right, the guide can't be sloppy enough to keep the valve off on one side and in fact the opposite happens with a worn guide....the valve rests at the easiest spot which will be as deep into the seat as it can go. with full contact of course!

that leaves what happened to the seats?

all I known is that it always happens over the exhaust ports for that side and if I recall correctly the same for the inlets. I just think if you hit something hard enough long enough then the aluminium behind the seat is going to give.

of course I now need to look for uneven seat to aluminium head interface....

regards

Taffy

bergbro said:

..Not sure I understand why the valve seat would not lap in squarly with a worn guide as I would have thought the valve would only move off centre when under pressure from rocker?

Click to expand...

i think that a worn guide would let the valve lap fully even if the seat to guide geometry isnt correct.
the slop in the guide would then cause the valve to not have a full seat due to any side forces alluded to earlier.

also, i dont know if berg guides can be knurled like car guides.

i think the disagreement is because not everyone is saying the same starting point.
i think taffy is saying that the guide is good and doesnt need replacement and that the seating is not full.

i think spanner n bushy are taking about a worn guide, which i commented on above.