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Couple questions regarding oversize pistons/valves

Posted: Fri Nov 08, 2019 12:16 pm
by rgould1910
On the 27 engine I rebuilt, I am running 80 thousands oversize pistons. This morning I discovered the reason for the pounding I was experiencing when I 1st started up the engine. The top circumferenceof the pistons are hitting the edges of the Riccardo head I installed. I am thinking I can remove the Ricardo head and re install the Ford head that came with the car initially or I can have the Ricardo head machined for clearance. What would you do ?
Another issue that comes to mind is I may have bent a rod due to the contact. I am not overly concerned because the contact is minor and I ran the engine for only a short time before teardown, but is it is an issue I would like some opinion on. A final question concherns my valves. In searching for the cause of the pounding, I removed the valves and checked them all for straightness. All are stainless one piece valves. 5 of the 8 were dead on straight. The other 3 had a slight warp in the stems. Total run out on the worst was one and a 1/2 thousands swing. I wouldn't think that little variation would be a cause for concern since I cut the valve faces and seats with Neway cutters and lapped the valves with Timesaver Green, but I'd like to hear what others think of that. As always I am very appreciative of any input

Re: Couple questions regarding oversize pistons/valves

Posted: Fri Nov 08, 2019 12:53 pm
by walber
I would relieve the contact areas on the Ricardo head. Take he head gasket off, use some Prussia blue on the piston head to mark the head, set the head on with 4 bolts loosely in place and turn the engine over with the crank. Remove the head and check for the contact areas. Grind the areas for clearance and recheck. IT might take a few tries to get it right but if it clears with no gasket, you will be good to go when the head gasket is installed and torqued. This is the same process that should be used with any aftermarket head as you never really know how much the block may have been surfaced, how accurately the head was machined, or in the case of older heads, how much they may have been milled.

I wouldn't worry about the valves but YMMV

Re: Couple questions regarding oversize pistons/valves

Posted: Fri Nov 08, 2019 6:52 pm
by rgould1910
Thanks for the feedback Walt. I think I'll cut a relief in the pistons. I have a set of 20 oversize that has a relief cut just above the top ring to avoid the situation I have, ie the top edge hitting the head. Can't understand why the 80 OS
I am using isn't the same. Here's a photo of the 20 OS.
20191108_152424.jpg

Re: Couple questions regarding oversize pistons/valves

Posted: Fri Nov 08, 2019 7:04 pm
by Joe Bell
Snyder's year ago fixed the relief in the pistons hitting head or head gasket from the relief in the pistons, I would look for marks that are shiny will tell you what is happening. I really hate going over .060 on bores! Just my thoughts!

Re: Couple questions regarding oversize pistons/valves

Posted: Fri Nov 08, 2019 7:08 pm
by Scott_Conger
Just had to lap those valves, huh? :lol:
With the Neway cutters you really didn't need to do that step, as they're designed to "pound in" in the first few seconds of running, since one seat is at 46 degrees and the valve is 45.
Just a step you didn't need to do...but I know old habits die hard :D

Regarding your question on injuring the rod. Obviously, never good to have this type of impact with reciprocating parts, but my suspicion is that the contact area was very small and the initial "ding" set the damage into the piston and subsequent dings were glancing blows which distorted the oil film on the rod but didn't do detectable harm to anything. I am assuming that while stiff, you could hand crank the car, and didn't detect a bind beyond what appeared to be stiffness. I personally would not worry and would use everything as-is after you relieve the pistons a tad.

Excellent learning moment to always check clearances with no head gasket in place and relieve things as necessary before a first start.

Re: Couple questions regarding oversize pistons/valves

Posted: Fri Nov 08, 2019 8:54 pm
by rgould1910
Thanks for the thoughts fellas. Joe, come to think of it, the 20 thou OS pistons with the relief were purchased from Synders. The 80 OS were not. Agree with you Scott and Walt about re necessity of turning the engine over w/o the head gasket before final installation. Lesson learned. Actually this is the first time I've used 80 OS pistons. Never had a clearance issue before. But then this car has given me a host of new problems and challenges.

Re: Couple questions regarding oversize pistons/valves

Posted: Fri Nov 08, 2019 9:11 pm
by kelly mt
I put a Prus head on a motor with 80 over pistons and had plenty of contact with a test fit and no head gasket. I used a bur on the head and got clearance. Every hole needed work. 80 over is tight with a HC head.

Re: Couple questions regarding oversize pistons/valves

Posted: Fri Nov 08, 2019 9:22 pm
by Henry K. Lee
Another point to is the fire ring on the head gasket if it has exposure will take a hit in distortion breaking down.

Hank

Re: Couple questions regarding oversize pistons/valves

Posted: Sat Nov 09, 2019 12:04 pm
by rgould1910
Gasket is Ok. Taking .100" off the top corners of the pistons. Having an adjustable chuck allows centering even with the cam ground pistons.
20191109_085542.jpg
20191109_085552.jpg

Re: Couple questions regarding oversize pistons/valves

Posted: Sat Nov 09, 2019 1:25 pm
by Joe Bell
I think you have the problem solved this way!

Re: Couple questions regarding oversize pistons/valves

Posted: Sat Nov 09, 2019 4:19 pm
by rgould1910
Thanks Joe for the encouraging words. I aimed for making the same relief I saw on the Snyder pistons I have.
I just now noticed the rod nuts have been touching the Stipe 250 cam and the oil tube. I used slightly longer rod nuts to balance the big ends of two rods. The interference is slight however and will require just a little work with a Dremel too l to create clearance on the cam. I can probably bend the oil tube out of the way. For some reason, perhaps the hitting of the head with the pistons, the babbit in the rods appeared shiney in spots. I once again used Time Saver and it cleaned up nice. Glad I pulled this engine after all.

Re: Couple questions regarding oversize pistons/valves

Posted: Sat Nov 09, 2019 4:31 pm
by Scott_Conger
Hard to see the piston issue as a blessing, but those nuts hitting the cam might have caused noise which could have been difficult to find, so going back through this again is time well spent.