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| piston-valve clearance https://slantsix.org/forum/viewtopic.php?t=65906 |
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| Author: | dakight [ Thu Apr 08, 2021 8:52 am ] |
| Post subject: | piston-valve clearance |
When I first started working on my engine I was very green and possibly made a big error. The block has been decked .100 and the head (if I recall correctly) was cut .060. I know that I will have to have custom length pushrods but now I'm concerned that I may have brought the piston too close to the valves. The cam is an Erson 270. What is the best way to check clearance? Is the compression ratio going to be too high for practical use? Do I need to put it together and turn it over, or is there another way? Fortunately I do have another block if needed. |
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| Author: | Dart270 [ Thu Apr 08, 2021 10:23 am ] |
| Post subject: | Re: piston-valve clearance |
It is highly unlikely that you will have this problem, especially with that small of a cam. The 225's long stroke means you usually have tons of clearance unless running a very big cam. One key question: Stock type pistons, or is the compression height different than stock? I have always assembled the shortblock, put play dough on one piston top, put the head on with no head gasket (or with very thin smooth washers under 4 of the head bolts between block and head), and assemble the rockers and pushrods for that cylinder (w/dough). Then I rotate the engine, being careful to stop if there is much resistance, and see how much depression the valves leave in the play dough. You can pull the dough off carefully and/or slice it in a cross section and measure with a caliper what the clearance is. 0.090" is typical lower limit. I would guess you'll be over 0.200". Lou Lou |
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| Author: | dakight [ Thu Apr 08, 2021 2:03 pm ] |
| Post subject: | Re: piston-valve clearance |
Stock flat top pistons, stock rods. I once measured the deck height but I don't remember what it was. I have the engine builder valves but they haven't been installed and I'm not sure I still have the stock valves but I'll look. At least I have some more confidence to go forward. I should be able to calculate the CR. Thanks for the help. |
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| Author: | Dart270 [ Thu Apr 08, 2021 4:19 pm ] |
| Post subject: | Re: piston-valve clearance |
Use the engnbldr valves if you can. Get the shop to roughly hog the seats out to the larger size, then get the head back and take a die grinder and blend the seats into the port. This will pick up a bunch of flow (and power) for not much work. You should have plenty of valve clearance. I have milled a head 0.140" and put in a 250 @ 0.050" cam with 0.500" lift with SB Chev valves (1.72/1.50) and there was still like 0.200" valve clearance. Lou |
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| Author: | DusterIdiot [ Thu Apr 08, 2021 4:52 pm ] |
| Post subject: | D |
D |
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| Author: | hyper_pak [ Thu Apr 08, 2021 6:15 pm ] |
| Post subject: | Re: piston-valve clearance |
Daknight, you are building a 225, correct? Because a 170 would be a completely different story. Your compression if using stock flat top pistons will be around 10.5 to 1. Around, you have to cc your head and make some other measurements and cam will effect the exact ratio. You should have plenty of clearance, but check with clay to be sure. |
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| Author: | dakight [ Thu Apr 08, 2021 9:34 pm ] |
| Post subject: | Re: piston-valve clearance |
I did CC the head a few years ago but I don't remember what it was, I'm thinking it was 65 or 66 but I'm not sure. I'll have to assemble one chamber and remeasure it I suppose. I do remember making them all equal. Yes, a 225 bored .040. |
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