You've gotta check! Each and every engine combination is different. You should check every cylinder, but if you have a lot of clearance on one cylinder, you are probably going to be OK.

Get some Play Dough or modeling clay and tear off big enough chunks to make small ***** of clay and put them on each valve on the cylinder you are checking. Put that one head on with the head gasket you are going to use, and firmly fasten at least all of the head bolts around that cylinder. Put both rockers and pushrods on that cylinder and tighten to the appropriate settings.

If you use hydraulic lifters, you would have to only tighten the rockers until you can't spin the pushrods anymore with you fingers. Then turn the engine over VERY slowly and watch that the lifters don't collapse during the test. A better way is to buy two solid lifters and temporarily install them for the test. Make sure to lube them VERY heavily and to just turn the engine over SLOWLY by hand.

After you remove the head, see how far the clay ***** have been smashed down between the valves and the piston. The thickness of the clay will give you your clearance.

I think that about .060" clearance is the absolute bare minimum and .100" is probably much better.

 

You SHOULD be fine - I used 601 heads with 1.94/1.60 valves on a 350 with flat top pistons and a cam with .490/.490 lift and had no interference problems. But it would still be wise to check, just to be sure.

 

You can't tell by the amount of lift and valve size. It also depends on duration and cam timing. The amount of degrees the valves open and close in relation to where the piston is in the cylinder will dictate the clearance. You could have a low lift cam grind make contact and a high lift cam with different valve events have lots of clearance. Advancing or retarding the cam timing can change the event numbers to add or decrease clearance. Using modeling clay is the only way to really know how much clearance you have.

Unless you have a really weird timing in the cam, I highly doubt that low of a lift cam will contact flat top pistons.

 

Guys, check me on this one because I've never actually done it this way, only read about it. I've always used the clay method too. But IIRC with the heads on the block and preload/lash set:

Another method is to mount a dial indicator parallel to a valve stem with its tip on the retainer. Zero the indicator and manually cycle the engine with the piston from about 30degrees BTDC to 30 degrees ATDC.

At every few degrees push down on the retainer to open the valve and to see how much clearance there is before the valve touches the piston. At some point you'll find the spot of minimum clearance. That's what you'll have.

I've recently read a hydraulic cammed engine can run piston to valve clearance as tight as .060" Intake and .100" exhaust.

Naturally you'll need to install a light spring to better be able to run this type of check.

"I was under then impression that the cam cant push the valves down enough to cause any damage."

T'ain't so; wrong impression. Also, remember, the piston is always chasing the exhaust valve and if/when it catches up BANG! That's what happens if there's insufficient clearance and the engine is over-revved, valves floated, lifters pump up, missed shift, etc.

I agree too that, based on what you posted, you won't have a problem with piston to valve clearance.

Jake

 

 

well another way to word this is: do 305's with the 58cc heads come with flattop or dish pistons?

 

Yes they do, and those (stock) 305s dont have valve clearance problems. But as Alky said, its not a head/piston issue, its a cam timing issue.

 

You could have a .700" lift cam with flat top pistons and never have a valve hit a piston however the opening and closing events of the cam would really suck. High lift cams normally need pistons with deep valve reliefs to allow greater timing events (more duration) for the valves.

As mentioned above, the piston is chasing the exhaust valve. The exhaust valve is closing as the piston is pushing the exhaust gases out of the cylinder. If cam timing is good, there will never be less than .100" clearance between the valve and piston.

The same goes for the intake valve. In that overlap as the exhaust valve is closing and the intake valve starts to open, the piston is now going down into the cylinder. If the intake valve opens too quickly, it will catch the piston and make contact. Intake valves can get away with .060" clearance as they don't get as hot and expand like an exhaust valve does.

Cam timing is based on installing the cam straight up.

If the cam is advanced it begins the intake event sooner. It opens the intake valve sooner. It builds more low end torque (many aftermarket street cams are ground advanced for this reason). It decreases piston to intake valve clearance. It increases piston to exhaust valve clearance.

If the cam is retarded it delays the intake closing event. It keeps the intake valve open later. It builds more high RPM power. It increases piston to intake valve clearance. It decreases piston to exhaust valve clearance.

With this knowledge, you don't go randomly advancing or retarding a cam without first knowing how much valve clearance you already have. Many aftermarket timing gear sets have a 3 way crank sprocket. It allows you to install the cam timing straight up or advanced/retarded 4*

 

so strait up would mean that the dots are at 12 and 6 on the gears. I have no idea what all this stuff means but the advanced duration is 280 int 290 exh. The .050 duration is 214 int 224 exh. I'm not sure what this means. The cam is a really mild performance cam meant to be just placed in the engine and call it day. However, I have 2.02 valves on 601 heads and I wasn't sure if the piston would come into contach with the valves or not.

 

I don't believe anyone can say or write with 100% certainty that you won't have a piston to valve clearance that's LESS than the recommended minimums. There are just too many variables involved. So many that the BEST any responsible person will say is that you SHOULDN'T have a minimum clearance problem.

Notice the caveat "SHOULDN'T". That word "SHOULDN'T" is predicated on everything having been done correctly and "right".

Without measuring, we have no way of knowing how the cam was ground, whether it was ground correctly (whether the cam card accurately reflects the cam you have), how the cam was installed, the timing chain set being used, the proper positioning of the dots on the cam and crank gears, etc. So there's no way for any of us to know for SURE.

If you're concerned about the clearances, you should check, measure and verify.

Jake