Blown engine. Ford 302 1968

[backdraft]

Rodbolt and other hotrodders, I,m doing long distance diagnostic for my brother a thousand miles away. He is buiding a hot street car for his kid. The engine was cleaned and honed but not overbored as it was allready 30 over. A summit racing stroker crank ,rods and pistons were installed. Aluminum dart heads, warm crower cam and hardened pushrods and assorted other hot rod parts were put in. The engine was run at 2 to 3 grand to break in the cam ,and all gauges for water,oil pressure ,oiltemp , fuel pressure, trans temp were OK. When the car was taken out and run, too hard I believe, it lost power. Due to the noise level, glass packs, headers etc,they didn't hear much and the drove it home. There was ZERO compression in two cylinders. #1 and#8 . Is it possible with the stroker crank and slightly oversized lower portions of the cylinder, the very shallow pistons got pushed sideways at the bottom of the stroke enough to collapse the skirts of the pistons and totally lose compression. He's sick to his stomach over what happened as this engine was BIG bucks. He hesitates to take it apart again but this is my take on the situation. I guess I just need someone else to concur on my theory of what has happened. nevjb

 

[Kenneth Brown]

Re: Blown engine. Ford 302 1968

Zero Compression? Thats gonna hurt. I would start with the most simple. Since the plugs are already out run a piece of soft wire down the hole to check for a piston. If it is there proceed to #2. Pull the valve covers and check for bent pushrods. A dead intake pushrod will not allow anything in therefore no compression. I doubt that the skirts could be collapsed that much. From here its pull it apart time. Good luck. <br /><br />By the way, I was incorrect on my order. The first step is to get the case of iced down beer ready.

 

[SS MAYFLOAT]

Re: Blown engine. Ford 302 1968

I'd pull the valve covers, crank it over and observe that the rockers are indeed opening and closing the valves. If not, then this is the problem. If the rockers are working like they surpose to, and still no compression whatsoever. It could be a broken piston, or if it had run lean, a burnt hole in the top of the piston. It can be possible of a burnt valve or two.<br /><br />Does it turn over? Do you hear mechanical noises when its turning over? Basically for no compression, there is a major leak in the combustion chamber.<br /><br />Good Luck.....SS

 

[LubeDude]

Re: Blown engine. Ford 302 1968

Guess I might as well get in here, Havnt posted in awhile!<br /><br />My take on this is (probably) There isnt enough clearance in the piston to valve train! Hard to tell without knowing all there is involved! Just throwing a bunch of parts together can be dangerous without checking clearances as you go! I always put a dab of modeling clay on the tops of the pistons and torque the head on and turn the engine over buy hand and then remove the head and see how much clearance there is between the piston and valves! To late to do this now!<br /><br />Sorry to hear about this, another lesson learned the hard way!! <br /><br />LubeDude

 

[snapperbait]

Re: Blown engine. Ford 302 1968

Overtightened rocker arms holding the valves open on #1 and #8...

 

[backdraft]

Re: Blown engine. Ford 302 1968

Mechanics all,Ken B. Zero compression . will not push your finger off cylinder when cranked over. Heven't tried rope trick yet. SS Mayfloat, rocker arms [1.6] and pushrods are moving . Nothing broken. Engine still runs,with a rolling idle. Piston [were] are heavy duty forged pistons from Summit. Car ran less than 2 miles. No rattling or banging sounds. Lubedude. Engine was put together by a machine shop except for ancillary parts. Snapperbait. I talked him through adjusting the number 1 cylinder on the phone , no good way of telling if they were adjusted right the first time. Still no compression. Zero on the gauge. I appreciate all the information and condolences. I'll pass them on. In the mean time , keep thinking and I'll pass on the findings when it's torn down. This happened yesterday, the 29th. nevjb

 

[rodbolt]

Re: Blown engine. Ford 302 1968

hello<br /> tell him to bring the affected cylinders up one at a time to TDC compression stroke. take shop air and blow into the sparkplug hole. ( we are going to use a quick,cheap leakage test) open the carb throttles. listen for air. I use a sheet of toilet paper over the carb and see if it blows off. then while still blowing air into the cyl, go to the exhast pipe for that bank and listen/feel for air.sounds like he may have swallowed, ooopps misshapen a valve. did anyone chek the piston to valve clearence at assy? it must be checked with clay. the min on the intake side is .080 and .100 on the exhaust. anything less and odds are they will not clear each other at some point. not knowing if the pistons were flycut or anything its hard to tell. usually a hole in the piston will cause a lot of smoke. if the air is hissing out of the valve cover breathers then you will know its a hole in the piston<br />post me back or email me at rodbolt40@yahoo.com if ya need more. been a long time since I did the hotrod thing. and why bother for less than 468 cubic inches <br />1970 W-30 442 4spd 3.90 posi <br />bought it in 1980 still got it but its rusting in this salt air

 

[backdraft]

Re: Blown engine. Ford 302 1968

I have sent all your advice to my brother to digest. Will keep you all posted. Thanks, nevjb

 

[CCrew]

Re: Blown engine. Ford 302 1968

One I've seen frequently...<br /><br />Insufficient end gap in the piston rings. Motor gets good and hot, put some power to it, top and frequently second ring butt ends in the bore and it has no place left to expand, so it cracks in a bunch of pieces. <br /><br />-Roger

 

[backdraft]

Re: Blown engine. Ford 302 1968

CCrew, It's a possibility. nevjb

 

[backdraft]

Re: Blown engine. Ford 302 1968

Thanks to all. The mystery is solved on the 302 Ford Hotrod engine.. You were all right in one respect or another. Using all your suggestions and Rodbolts slick was of checking for back pressure , the problem was found. There was a large amount of leakage past the exhaust valves. When the heads were removed, all 8 exhaust valves had hit the pistons to varying degrees. One and eight were sideways so to speak. The machine shop that put the engine together using the $1200 heads decided the spring pressure was to high and removed a 15 thou. spacer. This limited the valve float rev to 5500 , so says the mfg. of the heads. All 16 valves touched the pistons briefly, but only 2 were destroyed. The machine shop is now , today, argueing that the spring rate was too high ,but they are willing to redo the heads. All your ideas helped in the debate with the owner of the shop. My brother thanks you, I thank you, and a special thanks to rodbolt for the personal help. Mystery solved . nevjb

 

[backdraft]

Re: Blown engine. Ford 302 1968

Rodbolts slick WAY !!!! Damm fingers.

 

[LubeDude]

Re: Blown engine. Ford 302 1968

Goes to show ya, just because it was built in a machine shop dont mean they know how to build an engine!!<br /><br />Case Closed!<br /><br />At least the engine isnt destroyed!<br /><br />LubeDude

 

[LubeDude]

Re: Blown engine. Ford 302 1968

I was thinking about this last night and thought I would post it for you!<br /><br />Im mostly a Chevy guy and I know that the stock rocker arm ratio for the small block chevy is 5:1! I also think that the small block Fords are too! (could be wrong on this), you mentioned the use of 6:1 rockers on this motor! I think that with this cam and rocker combination that is the cuase of the problem! If I am right about the ratio of the stock rockers then do not put the 6:1 rockers back in!! <br /><br />If these peices were not put in by the machine shop, or he didnt know they were 6:1 rockers, then it wasnt his fault this happened!! <br /><br />LubeDude

 

[backdraft]

Re: Blown engine. Ford 302 1968

Lubedude, the machine shop installed the top end as well. And you could very well be right. The saga continues after it's bolted together. The engine is supposed to run up to 6500. Now if it was a Chevy. Just kidding Ford fans. nevjb

 

[rodbolt]

Re: Blown engine. Ford 302 1968

Dude<br /> Nev jb<br /> there is a killer article in this month hot rod or carcraft about rocker arms. off the top of my head I cant remember what the ratio was stock on you 302. most small block cheveys used 1.5 to 1. going back to what I posted earlier. anytime a higher lift cam or altered rocker ratio's are used it is imperitive that the cam be properly degreed and the motor assembled with modleing clay on the piston tops. if using hydraulic lifters you will have to pump them full of oil or use a modified lifter to install and rotate the engine and then remove the heads and check for how much valve to piston clearence is avalible. there is a definate problem and removing a .015 shim will alter installed spring height and it will alter the spring tension at spring fully compressed but it wont alter the amount the valve actually opens. I have truoble beliving that a .015 change in a shim will alter spring compressed tension enough for 1000 rpm difference in valve float. my stock springs on my 455 olds would do 6500 with no worries. I would keep looking as I think the valve kissing problem lies elsewhere.its kind of odd to float the exhaust as they tend to be smaller and lighter than the intakes. valve float is when the inertia of the valve motion overcomes the springs ability to close and keep it closed. valve float can also be caused by the hydraulic lifter pumping up and moving the plunger against the retainer. thus creating a pushrod that is now abouy .100 longer.the triple spring crane springs that I run on my olds have no problems at 7200 and I am still running hyd lifters. the first set of springs comp cams sent needed such a tall installed height that I would have had to mill the sping pad by .140". I called crane and told them what I had and they sent me these killer springs. so before I would reassemble and run this motor again I would call all the major players and tell them excactly what you have and see what can be done. you got lucky if all you needed to do was a valve job after kissing pistons. you should see a keeper failure at 9200 on a 355 chevy .<br /> good luck and keep posting<br /> who knows I may go back to hotrodding

 

[grampa's toy]

Re: Blown engine. Ford 302 1968

the 302 uses the 1.6 rockers. I had a similar problem with my ford with stainless valves. the shop clearanced the pistons for a big lift cam , but didn't check springs for bind . broke all 16 springs. It doesn't take much shim change to affect the spring rate, but with proper clearance you shouldn't get that kind of damage even with soft springs.

 

[backdraft]

Re: Blown engine. Ford 302 1968

Excellent points all. This is being forwarded as we speak. I believe you gentlemen are correct and another disaster is is around the corner. Hang on. nevjb

 

[backdraft]

Re: Blown engine. Ford 302 1968

Scholars all, The 302 Ford Hot rod blew up again. The valves hit the pistons rendering 2 cylinders with no compression. It was taken to another "top mechanic" where it was rebuilt again on the top end. A combination of light springs, thin head gasket and too radical a cam caused all the mayhem. BUT now this mechanic says the stall converter needs to be changed as the engine stalls all the time when the throttle is advanced from a normal idle.. To overcome this , he set the idle at 1300 rpm . This has caused the brakes to wear out prematurely. I advanced the theory that there was a vacuum leak or the mechanic was full of ####. I then suggested a new car. That's it. Thanks to all nevjb

 

[LubeDude]

Re: Blown engine. Ford 302 1968

This is disheartning as if as you said, "I blew up again" because there was enough information given that this should not have happened again! The general concensus was that the valve trane was the culprit and ways to test this were given. I guess you can lead a horse to water, but you cant make them listen??????????????????<br /><br />Oh, and by the way, your brother needs a new machine shop, It seems they only learn by trial and error, mostly by error. They should be paying for all this.