I have a 1988 f-150 302 Mazda 5 speed 4x4.
I rebuilt the engine last year and it has 5k + miles… has been converted to a Holley 4 bbl before I bought it so I stayed with that.
l was driving the truck pulling my little 4x8 trailer at about 65 mph on I-75 going into Chattanooga Tennessee. The Truck and trailer each had a pallet of bricks weighing about 900# each. I had driven about 100 miles at this point when all of a sudden I lost power and heard a clanking sound … I pulled to the side and it sat there and idled just fine but when I gave it quick acceleration it had the noise almost like advanced timing pinging.
I’m a praying man and asked for the truck to get me as far as He wanted me to go. I pulled back onto the freeway and continued with my trip … guessing I was running on 5 cylinders. Once I got it up to speed it would just purr along as always but getting it moving and going up Monteagle was a bear.
225 miles later I pulled into my destination … No change. So checking I had spark to all the plugs. Further checking I found 0 compression on cylinders 6 and 7 … not even a bump on the gauge with the sound as if I was spinning the engine with the heads off … all other cylinders are 115-120#, no blown oil. The vacuum gauge does have a bounce at idle but is in its normal range.
I have not drained the oil looking for metal yet because I don’t have a drain pan where it’s at. Before I get back to likely pull the head next , I’m curious what y’all think happened here.

 

It could have a blown head gasket between those two cylinders. Sometimes what will happen is the fire in cylinder that fires first in the firing order will light the adjacent cylinder through the channel in the gasket and make it spark knock.

 

If that did happen, ask yourself, did you clean the headgasket with an air power tool and pads? Did you clean the block too? If so, I have seen it more than once the gasket will blow between cylinders because you 'machined' that area so there is a valley.

 

So I’m back to start on the repairs on my truck … I was thinking it likely had a blown head gasket , but not even bumping the compression gauge on either # 6 or # 7 didn’t make sense for a blown head gasket. So today I drained the oil and I found no metal flakes in the oil and I even drug a magnet inside the oil pan. I know that blown pistons would account for no compression bumps and yes the pistons would not be magnetic but to run over 200 miles if its blown pistons would likely have something in the oil. BTW there was also no antifreeze in the oil either
I am leaning toward blown pistons at this point so I’m going to prepare myself for pulling the engine unless ya’lls got some ideas

 

Note to self … don’t use cheap head gaskets

The burnout was between #6 and #7

 

Check heads and block for true flatness, while your there, before going back together, what gasket was used?

 

I will check again the flatness before reassembling … looking closely at the gasket that is still together reveals that it is failing between the other cylinders also … I expect to find the same issue on the 1-4 bank also.
I used the Kit from Engine Tech that I bought from eBay … complete gasket set.. I used the same brand kit-on my ‘86 300 and had no problems with it … luck of the draw I guess. Probably go with the FelPro set this replacement

 

99% of the time when I see gaskets blown between the cylinders is because the previous cleaning job was done by an air powered cleaning disc. I've seen that took cause so much damage. Even worse when it was used on the engine block. Simple to fix a block, once the block is out of the car and completely disassembled.

 

I used a wire wheel on my old battery powered B&D drill … I did find that the head bolts above the exhaust were not nearly as torqed as the ones under the valve cover the instructions thst came with the gaskets gave a different torque setting and said do not retorque the heads … I’ll find out more when I get the passenger side head off and check for warping ect

 

Also note that the material between #5 and 6 and #7 and 8 are also damaged …

 

I'd be tempted to re-torque you passenger side before removal, that will tell you something.

 

Did you use new head bolts or reuse the old ones?

 

Probably what happened is the head bolts were all torqued to the same amount, 65lbs/ft with oil but the shorter bolts are now looser because the head gasket relaxed. The shorter bolts have less stretch for a given amount of torque which causes that to happen.

I've seen this be a real problem on Flathead Ford V8's and 8N tractor engines. The stock bolts or studs are extremely hard and when tightened to 70lbs they actually stretch very little. Then after a few heat cycles they are loose. What I do on those engines is just change it to grade 8 bolts and torque them to 50lbs. They stretch more and this allows them to stay tight. I've never had that cause a problem.

 

I saw a chart of load tests done with regular head bolts, g8 bolts, and ARP bolts; can't remember where I saw it. The test showed the g8 bolts stretched the most before yielding. Is there a concern with them losing clamping force as they stretch?

 

That's why I used less torque, only 50lbs on the 7/16 in grade 8's than with the stock bolts. When you torque them you can really feel the difference and 50lbs seemed about right. My idea was to get them to stretch more than the stock bolts so that they would tend to stay tight as the engine gets heat cycled over and over again and it seemed to work fine. I don't know how many V8's and tractor engines that I did that way but it was quite a few.

I have no idea what the properties of the original bolts that Ford used back then really are but they are very tough. Later Ford engines used more normal head bolts that were high quality. Also, sometimes when you look at a factory head bolt you can see how the shank of the bolt has had the diameter reduced. Shorter bolts usually have more of that done so that they can get an adequate amount of stretch where the long bolts don't need it as much to still stretch adequately. Otherwise they will tend to come loose after some heat cycles.