Piston to Valve Clearance Discovery
Posted by Glliw@reddit | projectcar | View on Reddit | 18 comments
Here's a little story for the group:
I have a 1990 Foxbody Mustang. From 1987 to 1993, they used effectively the same engine with a MAF sensor, pistons with valve reliefs, and the fairly OK E7TE cylinder heads. You would expect that a 1990 car then would have this flavor of Ford 302 in it. However, at some point in my car's past, someone swapped in a 1986 302.
So what's different about 1986? It has flat top pistons and relatively junky E6SE cylinder heads. Without the valve reliefs in the pistons, it makes cylinder head swaps far more problematic to accomplish.
Imagine my surprise when I pulled the stock heads off with new AFR165 heads ready to go on to find this fun fact about the car's engine. with a shred of hope, I checked piston to valve clearance and has about 0.020" of clearance with a generally recommended .080" on the intake and 0.100" on the exhaust.
This is when the car cordially invited me to cut reliefs into the pistons. Luckily, Lindy Tool exists and has a great flycutter solution to cut the reliefs with the engine in the car. It was a slow process of measuring and cutting the 16 reliefs needed but all in all it worked out, cutting to \~0.100" on the intake and 0.120" on the exhaust with the intent to have a little more clearance without going too deep to try and protect for a future cam upgrade.
So the moral of the story here is to just keep at it and roll with the punches. This is what makes project cars fun; finding the surprises like this and keep moving forward.
Tech1302@reddit
Thanks for posting this. Last year I put together a interesting combo that also used those 86gt pistons. I had taken a stock 86 gt motor apart and saved the rotating assembly. I finally got to use it on a 96 explorer. It ended up with 98 explorer block Gt40p heads 94 gt cam 86 rotating assembly 1.7 roller rockers Those 86 gt pistons are not only flat but also taller in the bore. The explorer pistons only have 4 small eyebrows but sit much farther down the bore. I measured the ptv and although it was tight I let it go and what a runner of a combo I found. That extra compression really woke it up. It would be interesting to see what cranking compression yours makes.
Solid_Enthusiasm550@reddit
You mentioned heads swap, but what cam did you switch to that you have such little piston-valve clearance?
What's the piston to deck clearance with the head gasket you are using?
Glliw@reddit (OP)
I didn't change the cam, though perhaps it has one of the Ford Racing letter cams or something somewhat mild in it from a previous owner; I didn't dig in deep enough to check that.
I didn't measure the stock PTV clearance personally as that head was trash to me anyways.
Generally speaking, the stock PTV clearance on a 1986 Ford 302 is very small. Take a glance at the warnings that AFR puts into their installation notes on the 1986 engine specifically.
I hear that if I had went with the Twisted Wedge 11R I wouldn't have had an issue given the valve angle in those heads, though I can't personally confirm that.
Piston to Deck clearance without head gasket was 0.009" or so without the head gasket. Compressed head gasket thickness is spec'ed to 0.041", so that puts things shy yet.
The silver lining to this mod as well is that the '86 flat top pistons are a touch higher compression ratio and the E6SE heads are more garbage than the E7TE heads I thought I had, so instead of bolting on a ballpark 60hp, it's more like 80hp (not dyno verified, don't murder me here lol).
smthngeneric@reddit
They're both junk. The best thing you can do is exactly what you did, throw them both away and get aluminum heads. Ford completely dropped the ball on all the factory heads that came on the Windsors... and then put some of the best heads ever on the Clevelands. Gt40 heads should have been the bare minimum, and they should have made something better for the cobra. I'll never understand it but it's all in the past now and modern day factory 5.0 heads (coyote) can support over 1000hp. Pretty insane how far head technology has come.
Glliw@reddit (OP)
Appreciate the comment, though I'll add that we should keep in mind that the engineering and design team responsible at the time had to balance multiple different competing requirements. It's easy for us enthusiasts to be Monday morning quarterbacks 30 years later when we are looking for more power. I definitely agree that technology has come a long way. If you told a consumer in the 80's that they could take their check book to a dealer and buy 700hp cars off the lot and daily drive them without much of any issue I'm sure they'd be shocked.
Solid_Enthusiasm550@reddit
You definitely had more clearance with the old heads, as they had smaller valves.
With a stock cam, what I could find is it was somewhere over .090" on the intake.
Glliw@reddit (OP)
Totally agree that the stock setup had sufficient clearance, otherwise Ford would've never rolled it out the door and I would've had pieces of cast iron on the garage floor if they didn't work. :) That's probably a pretty fair clearance for the stock parts.
Worldatmyfingertipss@reddit
This is when I call a machine shop. No way am I skilled enough to cut up some pistons.
Glliw@reddit (OP)
Ya know, I had the same mindset before doing it. You can imagine the range of emotions that I went through upon finding this out, lol. Generally though I'm a believer in the mindset that in the whole history of people doing things, there was always a first time for everyone so why not let this be my first time?
RBuilds916@reddit
I like your attitude.
Worldatmyfingertipss@reddit
Well you did give me the idea that I would still call a machine shop, but I would request a tech come to my house and show me how to do it properly and with the right tools.
qkdsm7@reddit
She's going to have some nice squirt with the afrs..... What cam?
On these I say if you can do heads and a cam, you should feel confident doing a flycut.
Glliw@reddit (OP)
I'm not exactly sure on what cam is in the car; I didn't change it with the head swap. I assume either stock or a Ford letter cam. I didn't feel compelled to bolt on that much more additional horsepower at this point. The car sees a fair amount of time in autocross and traction is already enough of a battle lol.
OlYeller01@reddit
I had a similar discovery in reverse. My ‘79 F-150 had the stock 302 replaced in it with a stock crate engine circa 1999. The original engine had flat top pistons with no valve reliefs and the worst heads Ford ever put on a 302 (D8 or something like that).
The truck sat for a while with the hood:/fenders off in a shop and the engine unfortunately got water in it due to roof leaks, despite being covered with plastic.
I pulled the engine out and started tearing it down only to find surprise surprise that the ‘99 crate engine, despite having the same junk heads, had valve reliefs cut in the pistons.
I could have had a better cam and heads on this thing for the last 25 years, and it very likely would never have sat. I was quite annoyed.
JcProject@reddit
What's thr story on the flycutter tool for making the clearance? Any pics/details on that?
Glliw@reddit (OP)
Good question! It was fairly easy to use, just very nerve-racking for a first timer.
I called up Lindy Tool and told the guy (probably owner, seems like a small shop in Chicagoland) what my valve and valve stem diameters were and he shipped me 2 modified valves. Super nice and helpful guy to talk to.
This video was the most helpful of all of the ones that I had found.
The general process overall was pretty slow for me as I was paranoid about making a bad cut. I did this all with the engine in the car.
I highly recommend using the measurement method for PTV clearance at the valve retainer. This is a good reference video for the method. I started with the playdoh method but that was very ambiguous to me.
juwyro@reddit
It's always fun finding out about stuff in the cars past. My 74 MGB had its brake and clutch pedal bolt come loose last night making the car undrivable suddenly. The PO didn't tighten the pivot bolt when he did the master cylinder.
I had a situation like this with my 89 Camaro. I cracked the flex plate doing reverse neutral bombs. The motor was swapped at some point in its past with an older motor. Needless to say the new flex plate wasn't balanced, I had to get an older one that was.
dscottj@reddit
The PO of my car? Lock washers apparently weren't his thing. When the mechanic I brought the car to took the valve cover off to start an adjustment, he discovered no lock washers on the cam or sprocket bolts. That would've been a fun failure. A few months later I noticed one of the exhaust manifold bolts was missing because all the lock washers were missing. Those were discovered when I first got the car.
Fast forward 25 years and I'm replacing the steering wheel the PO installed before I got the car. To my surprise, the lock-tab washer beneath the steering wheel nut was there. Said lock tab was wide open, of course, but it was there. This wasn't as panic-inducing as it might at first seem, as it took a lot of effort with a puller to get the dratted thing off.
The two owners prior to the guy I bought it from did other odd and exciting things: I've got a pinch on the nose that makes it resemble an earlier car, done so well I spent more than a decade thinking it was from the factory. I've got custom radiator mounts, because who the hell makes custom radiator mounts on an otherwise completely stock car? The top I took off in the early '00s had external quarter panel pads riveted to the frame that were again so well mde I mistook them as coming from the factory. When I asked my Alfa collective how to properly attach these pads, they asked, "what pads?" They now are rather odd-looking garage decorations.
The battery ground attaches to a radiator mount instead of its purpose-made mount because that mount is missing on mine. That's all I can think of off the top of my head, but I know there's more. Some of it is indeed from the factory!