Well the chap at the workshop was mystified but very good; his mill was set up for another job so he wouldn’t be able to check the alignment of the wonky bushes until the middle of next week. Instead he offered me a refund to cover the cost of a set of refurbished rods from a well known boutique workshop in Gloucestershire - although I felt this was too much so settled for just the refund for what I’d paid him. No hard feelings… and didn’t even need Big Barry. Trip to Moreton next week then.
Had a trip out to Moreton-in-Marsh yesterday to see James at Stateside Tuning (what a lovely part of the world!) and came home with a very clean set of weighted and balanced rebushed rods. It was great to look round his workshop - loads of top notch machines right for the jobs. Should have gone there in the first instance, and James was very helpful. One thing he told told me to watch out for is the clearance between the heads and the barrels measured between the top of the fin casting and the lower most machined surface of the head. With my feeler gauge I'm getting 0.33mm which I think should be enough but it would be great if anyone can pull out a reference for what the minimum gap is, please?
I’d be happy with a 0.33mm gap but I don’t have any references or know what it is supposed to be, obviously it would be more if you fitted a head gasket but don’t do that. Any gap is a gap but ask James what he thinks as you seem to be in his good books – he’s either helpful or he’s not.
I'd be happy with that also. I don't know why VW made this air gap so... non-existant. It's between the biggest fin on the barrels and the fattest on the head. Seems crazy to choke the air that could flow through here. I suspect, though he muttered about improved cooling, Rob was caught out by this after cleaning up the head decks though maybe not, I've got a nice big gap there whatever. Note the missing surface. You can see the gap-ish if you zoom in. Is that an improvement? No idea!
Good idea! I've just dropped him a note. I've done a quick back of fag-packet calculations that give tells me the barrel will try to expand by about 0.25mm over a temperature difference of 200 deg C, but of course it's constrained by the head bolts which makes it all pretty incalculable, for me at least. So 0.33mm clearance should be fine. Also checked the air gap between the first fin and the head at 1.1mm, so happy with that (James did say something about 1mm minimum, and now I know what he was taking about in that respect.) Thanks for the advice chaps -I'll pass on whatever James comes back with.
But not all at the head end. The gap @1/200th (guess) of the overall length would change by... a lot less.
To agree with @Zed . The expansion is less than you think.. Cast iron .. 6x10^-6 per degree C Aluminium 13x10^-6 per degree C Head and cylinder overlap maybe 5mm or less. Over 200C the head expands Code: 5mm x (13-6)x10^(-6)×200C more than the overlapped 5mm worth of cylinder.. or 0.007 mm.
Agreed - it’s an order of magnitude different. So I’ve stopped worrying about it and put it all back together!
Progress continues…. If anyone is having trouble fitting the air seal on the alternator I found you have to nibble a bit away so it doesn’t catch when you push the alternator back to get the belt on… Also, if anyone needs any grey sheathing (as you can see on the alternator harness ) let me know as I seemed to have ordered a mile of it. Happy to post a metre or two to anyone in need or find someone to take it to Tech Enders.
Friday puzzle time. Engine is pretty much complete but I found this at the bottom of the parts cleaner and can’t fathom where it’s from. Answers on a postcard?
