Will play-doh hold shape enough for checking valve/piston clearance?

Min safe gap depends on a couple of things like rod angle, max RPM, etc, but as a general rule of thumb, .050 intake - .090 exhaust.

 

OK, this project is on hold until I get that degreeing kit from Naford...

Always wanted to use one of those anyway...

I am surprised that the numbers are that big. I was thinking maybe .030 all around. Glad I asked...

 

I'm not going to give a MINIUM safe clearance Because there would be some would say this would not be correct. But one key thing to take into account when figuring the minimum clearance is lifter pump up. Although i will say with 30 thousandths preload, Bennett Racing recommend to me 80 thousands on the intake and 100 thousands on the exhaust On a stock roded 5.0 with iron heads.

 

If I am anywhere near .100, I will do more research before I start it up. Just to be sure...

 

.030 preload with the recommended .080 and .100 gives you .050 and .070 net (lifter fully pumped up and extended), which is pretty much standard. A lot of people will tell you min of .100 net on the exhaust since the exhaust valve is opening while the piston is coming up. It's good to get as much clearance as you can there. Since the exhaust valve is also smaller than the intake valve, you get more clearance that way too.

Since the intake is closing as the piston is coming up (both moving the same direction), you can run a slightly smaller clearance. I've seen as little as .030 on the intake, but would not recommend that for a street motor.

If your clearance is not big enough, you can move the cam advanced or retarded a couple of degrees with an offset bushing to get the clearance you want. It'll make the engine run different, but clearance is more important.

 

You know Scott.....you could have just asked for help. Typical safe clearance factor: .080" intake/.100" exhaust. I have run them a little closer but it must be checked. I'm off work all this week (we're closed for the week) so let me know.

 

I think Scott is playing in the water at the beach this week....

 

i never went through all this when i did the last 2 engines i built.. they worked just fine.

am i missing something

 

Shadow... i have called you 3-4 times in the last few months, with no calls back. So, i HAVE tried to ask...

Now that you are back, you can tell me what I did wrong.

And, i really AM at the beach jetskiing on this very WARM Christmas holiday. Feel free to come down for some beach jet-skiing...

 

It is snowing here, Perfect weather for building transmissions and working in the garage.

 

No way in hell am I getting on a jet ski. I may be nocturnal and cold-blooded but aquatic does not come into the picture.

Check your PM. Haven't seen any calls.....the number is in the pm.

Simon,
You are just assembling engines. You are not degreeing in a camshaft nor are you pushing the limits of valve to piston clearance with your camshaft profiles. There comes a time when you might decide to tinker with cam timing to see if the engine likes the cam advanced or retarded a certain amount. In those cases you should degree the cam and then check the available valve to piston clearance to make sure you have adequate clearance.

Got questions? Ask now because this is about the only time of the year I am in a giving mood.

 

that's questionable SD. They say on the ffw forum that you always give everyone a hard time all year long.

 

Bah Humbug.

 

I use modeling clay. Then put a little bit of flour on the top of the clay to keep it from sticking to the valves when you rotate the engine.

The intake chases the piston down the hole when it's at it's closest clearance.
the piston chases the exhaust valve closed when at it's closest clearance.

You should always check piston-to-valve clearance on ANY OHV/OHC engine that you're building, even a stock one. You never know when something is a little out of whack, and I guarantee you that it's much easier to fix it now than it is to have to take it all apart and fix what is damaged later. I recall someone who assembled a 440 Chrysler and forgot to check it..and bent every valve, damaged every piston, bent all 16 pushrods.....all because he didn't take 15 minutes to check the clearance. That was one of many expensive mistakes. In fact I've made those mistakes myself but at least I checked it before hand and knew that it was "tight".