New to me MK10+/G250 R109/108

[dstalsby5]

A

Keep in mind that you have a MK10+ according to your post and that is a very different animal than a MK10 IMO. Same exterior but all the working parts are different, and most of us that are fans of these prefer the regular MK10.

And I thought, I was doing good with the plus

 

[halocline]

A

And I thought, I was doing good with the plus

It was considered an upgrade because flow rates increased. And in theory, the blunt piston edge results in less HP seat wear. That didn't seem to work out well in the MK10+, they are known creepers. SP used the same seat and blunt piston in the MK20 and 25, and there were three generations of pistons; early MK20s had a steel slightly blunt piston, mid generation had a brass tipped more round edge, and then the late MK20 and MK25 have a composite steel/plastic piston with an edge somewhere in between the 1st two in terms of bluntness. That latest piston holds IP very well with the current seat. The brass one was a disaster and the early ones seemed to work ok but I don't know how long they held up before needing to be rebuilt. Anyhow, this is somewhat relevant to you because the MK10+ piston looks pretty similar to the early MK 20 piston. The difference is that the head is smaller, and that means less total force on the seat given identical IP with a larger head. That, in conjunction with the lack of a bushing system to keep the piston aligned more accurately, is probably the reason the MK10+ tends to creep.

Just in case you don't know what I mean by 'creep', it is when a little HP air leaks through the piston/seat seal and forces IP up gradually. Creep is indicative of a faulty seal and unchecked, it will cause the 2nd stages to start leaking. Creep is bad, in fact the way we check 1st stage function is by putting an IP gauge on them and looking to make sure IP 'locks' up steady and does not budge over time.