the flyin' scotsman

whats the VSC part # Rob? cant find it in PET

Following with much interest Andrew......looking forward to the re-assembly detail and the overall outcome

69gaugeman

You don't go looking for it. It finds you! lol

Imo000

The VSC is an easy retrofit but once installed it is nearly impossible and very costly to remove.

ptuomov

I think about it in a slightly different way. Not saying that your description is incorrect or anything, just that I think of it differently. My way of thinking about is the following:

The orifice between the pressure gauges flows a certain amount of air per unit of time, given the pressure on both sides of the orifice. If the pressure drop over the orifice is from 100 (absolute) psi to 95 psi, the flow thru a 1mm diameter orifice is about 0.70 SCFM. If the pressure drop is from 100 psi to 90 psi, it's about 0.96 SCFM. If the pressure drop is from 100 psi to 85 psi, it's about 1.15 SCFM. It's probably not too far from a square root relation in the pressure differential for given downstream pressure. Now, from the pressure drop you can tell whether more or less air is leaking thru the piston rings. In fact, you can compute it if you know things like the restrictor orifice diameter.

As a side note, I think that for comparable measurements one should really set the downstream pressure measurement to be a constant constant at some number. A drop from 200 psi upstream to 180 psi downstream means 1.92 SCFM flow. A drop from 100 psi upstream to 90 psi downstream means 0.96 SCFM flow. It's the same pressure ratio drop but double the pressure drop. It's not square root in the pressure drop because air compresses. But one should also take into account that the same cylinder and rings will "leak" a lot more when the downstream pressure is 180 psi than when it is 90 psi. So I think one should always test leakdown with the same downstream pressure (that the cylinder sees) or at least report the downstream test pressure along the pressure drop ratio if one has a fetish for precision. That said, if the flow thru the rings is about proportional to the pressure drop, it's not necessarily a bad approximation to just report the pressure drop ratio.

Now, what does the leakdown number tell us? I think that when the engine is not running, the ring end gap is the main cause of the leak down number. The leakdown in absolute is not very useful, it just tells you what the piston ring end gap is. But you already know that if you set it!

It is, however, very useful if one measures the leakdown with new rings and then measures it regularly as the engine has been run for more hours. The change in the leakdown number will indicate how much the cylinder and the rings have worn. As the bore wears or the rings wear, the effective diameter grows. Suppose the new engine bore diameter is 100mm, the piston to bore clearance is 0.04mm, and top ring end gap is 0.3mm. The ring gap area is about 0.012 mm^2. Suppose that this will give a "leak down" in a leakdown tester from 100 psi absolute to 90 psi absolute, and this will give some SCFM number. After engine has been used, suppose that the SCFM from the leak-down test has increased by 1/3, then the the ring gap has also increased such that the gap area has increased by about 1/3 (ball park, government work, etc.). If one knows the proportion of wear coming from bore vs. the rings, one can even compute an approximation of the new piston to bore clearance from the leakdown number.

AO

Back on topic.... here are a few pics of one of the pistons. You can see the slight carbon build up in the dish. Not a big deal. The rest looks fine to my eyes, but I do wear glasses nowadays.







Today, if time permits, I will start cleaning up all the bolts and pieces that came off the car. Maybe even start taking the heads apart to measure the guides.

Imo000

Thats a little more carbon then normal. The right side of the picture has a pretty good buildup. Use Permatex Gasket remover for the carbon. Spray it on and leave it for 5min.

Tony

Are those the original heads?
I dont see any pitting in them, nice... just discoloration....looks taken care of!

I used one of those fine dremel sanding wheels to get the carbon of the top of the pistons.


It will be nice to have ti all cleaned up. I hate the smell of burned oil..coolant etc after you shut down a hot engine.

atb

Looking good Andrew!

Can't tell if its just the angle of the pic (after that "moving T-rex" post in OT I'm not quite sure what I'm looking at anymore) , but is the WP impeller coming off the shaft slightly? I know you said its tight, but if the shaft isn't proud off the impeller, it would be good to compare it to another WP and see if your's looks the same.

Rob Edwards

Andrew- before you clean any piston tops, take nice pics of each top like you did above, and post them. If you note the periphery of each top, there's a carbon-free band- I'd be interested in Greg's take on its thickness. The carbon-free zone relates to how well the rings seal, though I have no idea how boost affects it.

ThetaTau87

Soaking the top of the piston overnight in a small container with Seafoam will remove the carbon completely.

Imo000

Nothing works faster and easier on carbon than Permatex Gasket Remover. 5 min and the carbon turns into liquid. I came across this by accident when working on another Porsche engine and have used it on other engines since.

BC

As another take on the pistons, those are very clean on the sides. Many times the rings get impacted into the groves because there is so much carbon.

The top carbon will slough off if you just sit them in berrymans for 24 to 48 hours.

No pics of the rods?

AO

Here you go Rob. I tried to get them as even as possible, but It's dark and the flash gives off a bit of a glare.

In order 1 through 8...











[img]https://lh4.googleusercontent.com/-_WpGxFjsJHg/UsitgxKpMzI/AAAAAAAAKEw/Z4iwTYZsEqM/w444-h592-no/IMAGE_323.jpg[img]





And for ***** and giggles here's a pic of bore #5. It's remarkably clear and void of any wear marks.

FredR

Andrew,

Nce photos- thanks for sharing. Always difficult to read anything from photos but if I was to do so I would say you have a well sorted motor which considering it has been blown for some time is quite remarkable and a testament to good tuning.

Understand you have had the heads off previously so not sure how long since last de-coke on the crowns [without re-reading the thread] but even so it does not look anything excessive. Will be interesting to read other more knowlegeable observations.

Regards

Fred

AO

Thanks Fred. I think it was about 5 years ago when I had the heads off last... Maybe 6 now that I think about it. I think not re-ingesting oil vapors helps.

I took all the bolts and other pieces to the basement for soaking in berrymans. It all just fits inside a folders can.



But then I saw what may be the beginning of an intermediate shaft failure. Need to get Greg to send me one of his new fangled versions. I think I dodged a bullet here. What you see here is metal starting to "gather" at the splines. Yikes!