SABB valve job

[AdeV]

When people know you've got machine tools, the damnedest of jobs start popping up...

A friend of mine recently bought a boat, complete with a rusty old nail of a SABB 10hp single cyl diesel engine. The engine turned OK, but required a new exhaust system and - when the head was pulled off, well... :



The head is quite badly pitted. The inlet valve was shut, so at least the seat of that has more or less survived. This should only need lapping in:



Unfortunately, the exhaust valve was left open, and the seat has entirely corroded away. The valve itself cleaned up nicely, but of course it has nothing to seat on:



There's no way I can simply cut a new seat into the metal, as it will have recessed far too far; so, the only option that I can see is a valve seat insert.

Therefore, my questions are:

- What material would be suitable for a valve seat, for a low-revving diesel engine?
- Should I try to make the seat myself, counterbore the head, fit, shape & grind it all in myself  , or is this a job best left to the experts  ?

I'm thinking of using an ordinary medium carbon steel (such as EN8 - because it can be hardened) to make the insert; which would be an interference press fit. I'd like to make it as close as possible to shape in the lathe, then harden & fit it, then lap the insert & valve together for a good fit.

So....

Am I on the right track? Any advice/ideas welcome...

[DavidA]

An engine re conditioner may have a valve seat of the correct material in stock. Remember that the aluminium heads have steel seats.  Also they will be geared up to do this kind of work.

No offense meant,  but if you screw it up then the head,  being old may be irreplaceable. You could lose a friend easily; and get some bad press.

Dave.

[lordedmond]

I totally agree with DaveA

Ade  to do the job your self you would need a piloted cutter to cut the seat , shrink in a new one , then use a piloted valve seat cutter , as you know it has to be concentric ,no compromise allowed



Stuart

[AdeV]

£350+ for a piloted valve seat cutter set 

Hmm...

The head is cast iron. The combustion chamber is heavily pitted, there's lots of slop in the valve guides... I think this head is already essentially scrap; so I'm not to worried about having a go, because there's almost nothing I can do to it that'll make it worse.

However... I would like to be as accurate as possible anyway... even if I have to make/adapt my own tooling... (I'd wondered about using a T-slot cutter, except I don't have one the right diameter... yet...

[krv3000]

HI  on thes old engines the valve seat is cut strate in to the casting ther is two wase to do this job 1 is to weld up the damiged parte then recut the seet or mack up a scruw in replasment as for recuting the seet you need a valve seet cuter see pic i have rebilt meney old engines with both metherds with no problems   regards bob

[Bogstandard]

Ade,

Bob has it spot on. Just got to be careful of any water galleries that are around.

If you are careful, you can actually cut the valve angle in the new cast iron seat as you are making it in the lathe. Then after it is fitted, it should be very close to what is required, and may even be grindable and lapable to aligment.

I have some nice cast iron left over from the Scott engine build if you get stuck, and if you want to accurately bore the head, my mill and all equipment for aligning it all up is here at your disposal.


John

[HS93]

Hi have you thought of NEWTONS ENGINEERS   or  John Lucas in liverpool  (havent used lucas since he re bored a marina block for my midget)  or even lane end up by me. they all do seats for petrol conversions. may  be cheap as it is only two seats and a od ball job.

Peter

[AdeV]

Thanks Chaps; I can see that the overall vibe is "probably best left well alone"...

Bob, I'm curious about the idea of screw-in inserts; how does one cut enough thread to get a decent hold of the new metal? I'd figured on boring a maximum of 1/4" into the head, and maybe 2mm oversize; for a fairly slimline steel seat. I'm guessing that to install a screw in cast iron seat would need a much bigger & deeper hole?

I am somewhat limited in that the valve is within 2.5mm of the cylinder wall; I don't really want to cut into that bit if I can help it...

[AdeV]

Hi have you thought of NEWTONS ENGINEERS   or  John Lucas in liverpool  (havent used lucas since he re bored a marina block for my midget)  or even lane end up by me. they all do seats for petrol conversions. may  be cheap as it is only two seats and a od ball job.

Thanks Peter, I'll pass those names on. The owner had tried the Birkenhead Engine Centre, who'd hummed & hahed & quoted over a hundred quid - which seemed excessive. Especially since I have previous with them, and unless they're under new management, wouldn't recommend them to anyone...

[lordedmond]

AdeV

A thought can you not buy off the shelf valve seat inserts ? after all all ali heads have them , you do hear of a lot of people who have had the seats done on the leaded engines. of course if you go back far enough to austin ruby days they had hard seats because the fuel did not have lead in




Stuart

[AdeV]

Stuart,

This is a diesel engine with a cast iron head... It's possible that I could buy an off-the-shelf insert that would fit, but it wouldn't be descibed as a "SABB 'G' 10HP exhaust valve seat"... because the engine obviously doesn't normally use inserted seats.

Cheers,
Ade.

[Warrenm]

Most replacement valve seats are just a square section ring. You cut the head to suit with an "interference" fit, press the insert in, then cut the valve seat using normal seat cutters using the valve guide as the centre.
http://www.5min.com/Video/Valve-Seats-Insertion-39413661

[Divided he ad]

Hi Ade,


I've still got 1 inlet and 1 exhaust valve seat insert from my days re-manufacturing landrovers. If you measure the valve and the internal of it's seat I'll see if either will do the job for you?

All you do is machine a recess into the head and knock them in, interference style!


Worth a measure?



Looks like you're going to be having some fun though   





Ralph,

[AdeV]

Hi Ralph,

The diameter of the valve head is 35.97mm (1.416"). The throat dia, as best I can measure it, is 30.97mm at its narrowest point, but it opens out again to 33.33mm (as best I can tell) about 1/4" in.

The biggest hassle I can foresee is the port slopes away from the valve seat very rapidly, on one edge; so there's not a lot of meat for a seat to dig into, on one side. It would, I think, have to be quite a shallow seat.

Dunno... I'm going to take it to Bogs this w/e for his considered opinion.

[doubleboost]

I have had valve seats fitted in to mini cooper s heads
the head was machined then a seat machined to be a shrink fit
the head was warmed up and the seat cooled (very cold )
then pressed in
As far as i can remember non ever fell out
The bloke that did them gave a guarantee (if it falls out you can have your money back)
He did not like doing them and only did them for people who were prepared to take the risk
On a low reving under stressed marine diesel you should have no problems

[krv3000]

pic

[krv3000]

pic

[krv3000]

HI sos for not geting back sooner but me intrnet went off right as regards to threding for a valve seat replasment with this low reving engine anything will do i have even cut into water jacets to reper them 1 set up in the mill by yousing the valve gide to set it up on center with the ade of a boring hed tack out just the amawnt need to form a new valve seat + thred i youse fine mm thred  mace up new valve seat  the way i scruw the new seat in depens on the overall od but the way i normaley do it is by leving a large ring at the top in to wich i drill in too for c spaner lick the type you youse to remove your grinding discks from your angelgrinder i have scruwd them in with nothing on the threds and i have scruwd them in with locktite plumers tape red jonting compawnd all with no problems i can if you wish lend you my set of valve seat cuting tool if you is preperd to pay for the postige to you and back to me   regards bob

[AdeV]

I've decided to mock the job up on the mill, to see how difficult it is to line up the cutter with the valve guide.

1st job, find 4 level risers to raise the head off the mill bed. As luck would have it, my recent lathe tool gloat contained 4-off clamps, which when sat on end, happen to be dead level. Chuffed? I was... So, using the 4 head bolt lands as a reference the head is mounted & clamped.

Next up, I turned down a piece of scrap brass tube to 0.351" dia - exactly the same as the valve stems. This was then mounted in a collet & checked for runout in the spindle (about 0.001"). Finally, the head was manoevered under the spindle until the brass rod cleanly passed through the valve guide.

Here it is in the "up" position:



...and down...



The bottom of the brass tube can be seen poking out of the top of the valve guide:



After that, I blued it up & passed it through again, to ensure that the blue was removed uniformly; thus ensuring an absolutely dead centre (within 0.001" anyway) on the valve guide. The valves themselves wobble about by at least 0.010" anyway, so IMHO this is plenty close enough for the job in hand.

Next up will be to actually get a round to visiting another friendly MadModder who has some valve seats going begging.

Hat-tip to Bogs for a) spotting & pointing out the 4 datum points on the head, and b) suggesting the valve-guide-in-quill to get it centered up.

 

[Divided he ad]

Looks very nicely mounted    Good enough for a skim too?

Paper shims, nice sharp flycutter and a really slow feed? Or if you know someone with a surface grinder big enough you could get a hell of a good finish on cast iron 

Couldn't clamp it like that though?!  Maybe a clamp or two in the holes in the sides of the head? Anywho, that's a bit further down the line.




Valve seats.... I'm sure I had some somewhere?   






Ralph.

[Divided he ad]

           



 






Ralph.

[AdeV]

  * eh? What? Who?

Sorry, been busy away from the machines.... and I'm too knackered to do it tonight (I'd be dangerous on a machine tool tonight).

Tomorrow.... maybe 

[Divided he ad]

    I know you've only just got the mic' for the bores.


No hurry, just thought I'd wake you up     I can talk, the amount of half done things in my workshop!


I just want to see the result with the seats 



Keep us posted.






Ralph.

[AdeV]

No worries Ralph, I'll be getting around to it soon...

First job is to further bore out my practice ali piece, to make sure I can hit the dimension with the boring head. Assuming that goes well, I can crack on boring the actual head out, etc.

More news Real Soon Now

[AdeV]

Well, that took longer than anticipated....  

Right, first up, in true Oscars style, I must thank a couple of people:

 - John Bogstandard for lending me his boring head, cutters to suit, and an internal mic to measure the bore with. Couldn't have done it without them.  
 - Bob aka krv3000 for kindly donating a valve cutting tool to the job (at least, I hope I understood correctly & that it was now donated.... if not, I owe you a new body, you'll see why in a minute). Another due.

So, on with the show. First up, I cut a test bore in some aluminium. The aim, to hit the exact dimension + 1 thou, of the seat insert:




It was a bugger to get in there, but once in & seated, it revolved easily. Mission accomplished  

Filled with an entirely misplaced sense of optimisim, I put the head back on the mill, reset the boring head & got cutting. I took a fairly shallow initial cut of 0.050", figuring I'd want at least 0.100", and preferably a bit more if I could get it. So... I merrily made a few cuts, then measured; AARGH, 0.005" over!!! Nightmare.

Not to be dissuaded, I took another set of cuts, as deep as I dared (about another 0.075"), being much more careful this time. I got to within a thou and a half, & decided to go for the interference fit.



Anyway, long story short, it didn't work, and I ended up with a cracked valve seat insert. So, plan B (again, thanks to Bogs for suggesting this one).

I drilled 3x 5mm holes, plug-tapped them M6, and inserted small bits of M6 threaded bar, with a screwdriver slot hacksawed in the top. The result is this:



The valve seat is still a good tight fit (in the bit I didn't overcut), and the three screws lock it solidly in place. I then milled the screws flat, and set about cutting the valve seat to shape/size. After using the hand operated valve cutter, as supplied by Bob, for about 5 mins, it became clear that this was going to take an eternity.... so, I modified the body of the tool on the lathe to fit a collet, then I could machine mount it. With the mill in back gear @ 67rpm, the valve cutter made short work of the job. After a couple more goes, I'd got it ground down nicely:



The exhaust valve (with the slot in it) sits about 0.005" further out of the head than the inlet valve; that shouldn't cause any problems on this engine:



And the fantastic valve grinding tool (with modified handle and home-made brass valve guide):



The head has gone back to the customer (luckily I persuaded him to lap in the valves, a job I hate with a passion), will bring news of its working (or not) as & when.

So, with that job out of the way, the time has come to pack the machine shop up & move it to its new home. Fortunately, that's just down the road, because having loaded a few bits of kit in the back of the car, I did rather worry for the suspension....:



Glad I'm not moving the machines in the car!!