its was a standard bottom end with only 1000miles on it when i got it in 1997 so it hadn't been played with , when i stripped it down to rebuild it that's when i noticed the marks on the pistons.
Looking at that pic of the gasket, both piston would catch on the sides and defiantly the front area infront of the inlets, so I'd rule that out straight away. I'be also been chatting with several people over the last few days who have fitted kr heads to abfs and none have had issues. How far do the pistons stick out above the top face? As the abf I just stripped didn't stick out at all. And again, the front of the piston(being level with the crown on an ABF) would have to avoid the front of the head.
Was the head gasket correctly located on the dowels to centre accurately over cylinders? And was it a KR gasket as this has a smaller bore diameter? Std bore 2.0, with 82.5mm pistons? Not a rebored block?
Dan - 2.0L Head Gasket p.s. that's Toyo's hand on the pictures Martin - 0.5mm its in the VW Spec for the ABF (piston deck height) i've rebuilt 4 ABF Engines and they are all the same. the piston clearance isn't an issue when you use a steel head gasket 1.2mm , its when you use a standard head gasket 1.0mm anyway just thought i would share my experience on this one. Just something to keep in mind if your builing a high RPM Engine with high compression pistons. If your building a stroker with 9A Pistons its not an issue as the Deck Height of the 9A Pistons is 1.5mm lower than the ABF Ones. Wossner ABF 9032D Piston comp height 31.6mm Wossner 9A 9031D Piston comp height 30.6mm previous thread http://www.clubgti.com/forum/archive/index.php?t-157590.html ABF KR Pictures from Toyo's back yard !
Still doesn't make sense though. You can't argue with figures so with a 20 though deck height, and a gasket of 40, theres a 20 thou gap. I can't see the rod stretch being 20 thou, and even if it was there would be contact at the front of the head also. is there evidence of contact infront of the inlets? I'm not arguing, but the facts and figures are saying that if it catches the sides of a kr head, it would also catch the front of a kr and also an Abf head as this area pertrudes into the combustion area at the front of a level piston. Were there hammer marks on the sides and front of the kr. combustion chamber? There should be something on both, maybe evening peening over of the lip?
Surely if the piston caught the edges of the head then it would also clout the flat section of the head between the inlet valves. Erm yes, what Hotgolf said. Also, I ran a factory KR head on my ABF to begin with and I didn't have any issues. I also didn't have an increase in compression, torque or power. In fact the ABF head did better. Both heads were decoked and seats lapped before use. Gurds
I can see the marks on brooksters pistons and head, could they have been made in another way to direct contact? maybe det? if the gap between head and piston was so close now the angular parts of both suffered det? or extreme heat?
Looking at the pistons Brooky put up, it would appear if you have an ABF engine with high compression ABF pistons that brooky had/has, capped off by a KR head, without reworked combustion chambers, you will clout the piston on the non thrust piston perimeters. Based on the pictures with the gasket if the same engine was capped off with an ABF head this would clear ( just about). The high compression pistons appear to have the area for squish pads near the inlets lowered meaning that that you should not clout this area and head gasket thinkness as Mart stated should suffice. The use of a KR head on an ABF engine with std pistons, is not a problem as Gurds/Mart just stated. Which is better - The ABF head is. Why - It has many opimisations based VW marketed power and torque, EU fuel economy and emission requirements, customer expectations and the base engines this head would be fitted to. Here are some of the improvements that have been observed and reported by the CGTI collective: Small 27mm dia exhaust valve on 27mm seat for improved flow of hot exhaust gas Cooling passages in the exhaust port to reduce hot spots and improve durability Cooling channels in inlet port to improve/vaporisation and wall warm up. Cooling passages in the combustion chamber to reduce hot spots and improve durability. Improved squish areas working with revised piston. Optimised valve shrouding on the inlet toward spark plug hole optimised head shape around the shrouded part of the exhaust valves. Reduce valve guide protrusion. Reduction in port casting imperfections. In/Ex Port flow improved over "51***373" as seen in JMR flow analysis. Compression difference - Debatable but will be soon validated. Valvetrain weight - anyone? These features all interact to allow the base engine to achieve improved burn, power and torque while passing emission/CO requirements for that era. These properties mean the above head is great as a base when the focus turns to tuning.
I've seen Brookys old H/C Wossners, with the tapered tops, yup, tappety tap on the sides from contact, but the std ones will be fine. You could always deck the block, mod the tops and raise compression though and will be fine as long as you don't go mad taking too much off. I may have to start my ABF head and eventually see what gains can be made, although I'm a looooooooong way off.I do like the chamber shape in the ABF's, you can see the advantages straight away.
I have a ABF Head in the workshop as a spare would be interesting to see if there are any great gains with that head design. It maybe a few years before i ever fit that one too .
