Thunda Babe

[Bob Vic]

Big end bearings eh! The mention of these brings out my nervous rash. I'm sure that you'll be fine.

[WoodRay]

Cylinder head is nearly finished. I've all but finished the new thicker wall chrome moly rocker shafts. All that is left to do is for me to knock up one more additional rocker pedestal. The centre pedestal pad area has to have a new solid BSP core plug fitted. This will be cut to the length required then fitted tight in the head, machined down to the head face, and then drilled and taped for the pedestal stud. I've now gone from 4 pedestal supports to 7. This should strengthen things up a bit.
My big end bearings arrived yesterday so I can finish the bottom end serious stuff very soon.

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[Bob Vic]

Mate you are a marvel at what you can achieve with a lathe. I can only look on in awe!

[WoodRay]

Oh the joys of working on old stuff. Today's new hurdle is my new piston domes do not match the shape of the cylinder head combustion chambers as they are fouling by about .170" in the areas circled. I've had to spend considerable time ultrasonic thickness testing the chambers and domes to see what material I can remove safely. I'm also suss on my supplied dome cc size so will have to check the dome cc volume in the cylinder. This is a bit of a set back, one that I wasn't expecting. I'm hoping I don't loose too much in the compression ratio depending on how much material I have to remove. I'm not sure how this conversation will go with the manufacturer either. I've also got some serious overhang shrouding between the bore and head around the exhaust valve. This is an initial design problem that I'll have to nut out. Engineering the impossible here we go!

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[Greg]

Bloody hell Craig!

[Bob Vic]

Ouch... if anyone can nut this out and work through it, it will be you Craig. You make woodwork look easy.

[Alan]

By the look of the valve relief you should have enough, have you worked out how much you need off? How much CR are you looking for?

[WoodRay]

By the look of the valve relief you should have enough, have you worked out how much you need off? How much CR are you looking for?

It's not the valve relief that's the issue. The taper on the crown is hitting the chamber where I've marked them. The older designed pistons had the inlet valve relief as a milled flat across the full diameter.

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I think their design change is the problem.

It's supposed to be about 10.5:1 with their figures using a 15.6cc dome. My chamber is 51cc. I'm thinking it should be 10.8cc dome by my calcs but I still need to work out my crevice and gasket volumes as this maybe where the discrepancy is.

[Alan]

I understand where its hitting but was going by the amount removed, it's hard to know without seeing the under side shape. I would trust your calcs more as you know your gasket type and have the physical parts to check. (Does look a big lump for 10.5)

[WoodRay]

Going on a rough gasket volume of about 5cc it looks to be the right size in the dome if it's 15.6cc, but will physically check it all. It's bloody disappointing considering how much they cost. I will have to speak to them to see why they changed the inlet valve relief from the original design and added an exhaust valve relief when it's not required.