Just one opinion, but if you are ending up with 1mm. raised ports in a '74 H2 engine, you are going to be in a good place. I wouldn't personally be too worried about the situation you are describing!
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| Author: | Never2Old [ Wed Aug 09, 2023 4:17 pm ] |
| Post subject: | Re: Piston height above deck |
If they shave material off the top then won't any spacing under the cylinder will throw off the port timing? Does anyone make a "thick" head gasket? Dave |
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| Author: | mraxl [ Wed Aug 09, 2023 4:51 pm ] |
| Post subject: | Re: Piston height above deck |
Yes, I believe it is Cometic that will make gaskets for base or head any thickness you want. |
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| Author: | Never2Old [ Wed Aug 09, 2023 8:13 pm ] |
| Post subject: | Re: Piston height above deck |
Yes, I bet the tops were shaved. I took the picture with the cylinders upside down just to show the difference in the height. If they shaved the cylinders, I wonder what else they did to make it all work. Custom heads? Custom rods? I'm not familiar with techniques for building high performance motors but simple geometry says that if you shorten the cylinders, something else has to change too. Is there any option for using these or should I just look for a new set of cylinders? Dave |
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| Author: | mraxl [ Thu Aug 10, 2023 7:23 am ] |
| Post subject: | Re: Piston height above deck |
One method for enhancing performance is to put in an increased thickness, 2mm or so, of base gasket to raise ports. Then the tops of cylinders need to be shaved by the same amount to restore compression. I think you must have a cylinder where this has been done. At one time lift kits were offered for triples... it was an easy way to "port" cylinders. If I had what you have I;d do some measuring and use the cylinders. How many cyls are this way? All or just one? Are we talking about H1? You might also want to measure port sizes to see if they have been altered. |
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| Author: | Never2Old [ Thu Aug 10, 2023 8:37 pm ] |
| Post subject: | Re: Piston height above deck |
It's a 74 H2 and I'm pretty sure all 3 cylinders are the same height. If they took 1 mm off the top then a 1 mm base gasket would solve the piston interference problem but it would throw off the port timing. I haven't measured the ports yet and I don't know what 1mm would do to the timing. Anyone in southern New England good with port issues? Dave |
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| Author: | RODH2 [ Fri Aug 11, 2023 5:38 am ] |
| Post subject: | Re: Piston height above deck |
Just one opinion, but if you are ending up with 1mm. raised ports in a '74 H2 engine, you are going to be in a good place. I wouldn't personally be too worried about the situation you are describing!
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| Author: | mraxl [ Fri Aug 11, 2023 6:25 am ] |
| Post subject: | Re: Piston height above deck |
First you must determine how much material has been removed from top of cyl... call it "X". -If you put new gasket (X+std head gasket thickness) under head then original timing is restored. -If you put new gasket (X+std base gasket thickness) under cyl then new timing is made. Assuming amt shaved is ~1.5mm then I would use new timing... it will help performance. Compression afterward should be ~145-150psi. |
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| Author: | Never2Old [ Fri Aug 11, 2023 7:18 am ] |
| Post subject: | Re: Piston height above deck |
Thanks for the feedback. I think I'll try a thicker base gasket and measure the squish to make sure I'm where I should be. It's the easiest way to go without buying any expensive parts. I'd hate to waste the nice job they did boring the cylinders and fitting the new Wossners. Dave. |
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| Author: | ALTERED IMAGE [ Fri Aug 11, 2023 1:53 pm ] |
| Post subject: | Re: Piston height above deck |
No! listen to mraxl. MEASURE so we all know what you have capich? cliff |
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| Author: | Never2Old [ Fri Aug 11, 2023 8:42 pm ] |
| Post subject: | Re: Piston height above deck |
Okay, here are a few measurements I was able to take, pictures attached. The first two images show the cylinder heights, measured from the base to the top of the cylinder. Base gasket surface to head gasket surface. Dave |
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