2L Fiat TC Cylinder Head Valve Seats

[sk2877]

Guy,

I'm in desperate need of some advice on my cylinder head. I had the coolant galleries welded to add more material to the port walls in anticipation of going agressive with porting and polishing as I found recomended in your workshop manual. I've got the galleries for the most part cleaned up to the depth that I would like (added about 3MM per port wall) As a result the head expanded around 3 of the valve seats. (Photos are below and the problems have been pointed out with a digital black arrow. I know the head looks pretty rough at the moment, but any further machining is on hold until I come up with the next course of action. Am I able to put in larger seats to fix this, or is the head a large paper weight at this point? If by chance, larger seats will fix this, and I see you offer them, how much larger than stock are they?

Thanks in advance!

Steve

[Guy Croft]

New inserts needed which FWIW I can supply quite readily either in high strength copper alloy (Columbia Metals 'Trojan) or the cheaper sintered ni/cr/fe alloy. For now froget about that and 'chase out' (remove by fettling) the old seat inserts right now by breaking thru the cast iron carefully with a small cylindrical carbide in a high speed die grinder and, once the stress is broken they will prise out with a screwdriver. Avoid as far as possible 'collateral' damage to adjacent regions.

Then get on with your porting, the valve throat region should be left alone for now. After porting the new guides can be fitted and a 'How to' is attached.

New valve insert size will follow valves and the first criterion is that the OD of the insert should always be at least 1mm bigger than the valves to prevent edge fracture after the 45 deg contact face has been ground (or cut). The bore in the head (recess) for the new inserts will have to be first 'trued up' ie: corrected for circularity and flatness at the bottom where the insert sits, and then accurately bored either a) to give correct interference fit on the as-supplied KS sintered inserts or, b) as in the case of the copper alloy ones the inserts will be made to suit the finished bores. It is usual for the ID of the insert to require boring after fitting and this dimension will depend on valve diameter and seat width/angles which we can cover later. It is best to fit inserts that are taller than final height by 1mm or more (ie: stand proud of the chamber) so that they can be 'topped' with an optimum top angle without upsetting the valve tip setup height. The bottom of the recess for the inserts should not be any deeper than required to 'clean up' (it won't be flat) give a good mating contact.

It is important to note this:
Fitting new inserts always means alteration and correction to the short side radius and correction to the alloy section of the port after fitting. Once the insert has been shrink fitted (which they MUST be) using liquid nitrogen and heating head ot 150 deg C - the valve 'throat' (ID - inner diameter) is bore parallel to a dimension set by valve angles of 45 and 70 deg, and the boring op should be done with a radiused cutter so that you can bore thru the insert into the alloy region to a depth of about 3mm BELOW the actual insert. This gives you a dimension to work to with the die grinder without the burr and abrasive bands impinging on the shiny new insert - which if copper alloy will easily be wrecked by incautious fettling.
Fitting a bigger insert also can allow you to improve the short side radius profile by exposing more material to work on. Some models have a low port floor - notably the big port 43.5mm inlet valved Lancia Volumex and Fiat Strad 130TC - their short side rad is almost non-existent but the fact is that the optimum port shape is round (although not all heads have round ports) because that gives the best velocity distribution and sometimes - depending on cam profile - it really is necessary to sacrifice the SSR to an extent to get better high lift flow. I'd go so far as to say that it is impossible to get a perfect combination of high and low lift flow (with valve in) on a sidedraft port like the TC. You'll either make it fabulous at high or low but not quite both! Now the bigger radius you can develop after fitting a big insert gives you a choice: You can remove the bulk of material from port sides and roof and 'go easy' on the port floor keeping a generous SSR curvature - or head for low floor with minimal SSR and big, round port. I have done and dynoed both, though not directly back to back, and have achieved (which few actually have) 200bhp on a 2050cc big valve TC with a very radically altered floor and modest SSR and at the same time done the opposite and achieved better spread of torque at StIII levels of tune. There is no easy answer really. A lot depends on intended use and cams (and as far as CR goes of course, the more radical the cams and bigger the valves the higher CR you need).



So, and I hope this helps, new inserts can wait for now! They are a much later op.

GC

[sk2877]

Guy, thank you for your prompt and detailed response! I've got a lot of work ahead of me, but I can sleep better tonight. I lost my original head to a poor welding job by someone whom was "Highly recomended" from a number of sources. He used a stick welder and burned through the coolant galleries into 2 of the intake ports. As a result, I had pin holes (by pin hole, I mean 1MM in diameter) that I had welded by someone else 5 times to try and plug. Turns out he was drinking on the job, and as a result I lost a cylinder head with at least 3 days of work on my part, and propably 2 days on my machinists part, not to mention the money lost, or the fact that the numbers no longer match. So if anyone out there is thinking of going down the same road, beware. I found a phenominal welder just outside of Washington, DC and I'm more than happy to pass his information along to anyone in need. Thank you also for the airflow and guides documents. I will definitely reference them while I'm working on the head. I'll post some pictures once I've got the seats out and as I'm porting and polishing, along with the final product. In the mean time, since I'm state side, I'll order the larger seats from you along with a few other tid bits, so I can have them on hand when I'm ready.

Thanks again!

Steve