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SB Chevy that will only turn 1 revolution...

4K views 14 replies 8 participants last post by  sunrise7 
#1 ·
I have a small block Chevy engine that is currently mounted on my engine stand. The oilpan, intake and exhaust manifolds, and valvecovers are off.
Heads are on with sparkplugs out. From below, all looks good with pistons, rods and crankshaft. Here's my problem.... I can only turn the crank one revolution ( by hand ) and then something jams and stops it from turning any further. I loosened all the rockers to rule out a stuck valve. Distributor is not in either, so nothing can be jammed on that end of the camshaft. Any ideas ??
I was thinking maybe something got into one of the two cylinders that have the piston coming up to the top at the point where it always stops turning or maybe something wrong under the timing chain cover, it is still on, like a problem with the chain ... but how likely is that since it does turn quite effortlessly for one turn ..... What should I check ? Thanks....
 
#4 ·
Because of the longer stroke it's possible for the big end of the connecting rod to hit the cam as it passes by. Usually stock rods with regular nut and bolt type rod bolts. #'s 1, 2, 5, and 6 are the most likely to hit. Some people think that small base circle cams will fix this but not always. It usually depends on what rods you're using. Clearanced cap screw type rods are usually your best bet for having enough clearance out of the box.
 
#11 ·
383 strokers have three (3) possible points of interference between the rods and internal surfaces and the cam. These can be the pan rail, the bottom projection of the cylinder walls into the crankcase area and the camshaft. Not all blocks have all these interferance points as there are differences between castings that may or may not allow rod clearance with a stroker crank. The cam can be counted on to be an all the time problem however. So you need to check the clearance all the way around.

Generally, capscrew rods have fewer clearance problems than do conventional bolt and nut arraingements. But even when using stroker clearanced rods you've got to check these interference places. It's considered that .050 inch clearance is sufficient, it ain't much though. When it comes to grinding the block especially around the cylinder bases don't remove more materail than absolutly necessary as this area can be thin. The bolt and nut rod unless its the 400's 5.56 inch job will require grinding on the bolt head, while considered safe in the popular press, I can't and don't do it, that's the kind of thing that will keep me awake at night so I always build these things with a cap screw rod, for a budget street perfomance engine/claimer/ even a rules Sportsman my choice is the SCAT ProStock or ProComp >>> Scat Crankshafts <<<. My preference is for the floating pin configuration in the 6 inch length. But there's nothing wrong in using the press pin nor the 5.7 inch rod.

Bogie
 
#9 ·
sbc only one rev

Is this engine on the stand upside down? there are soo many things that could do this and not all are bad, ive had a stand that would lightly catch one of the bellhouse mounted bolts that hold it up hit an arm on the stand, Is the fuel pump still bolted to the engine(if mech pump)ive had a pump rod jam me up before also,will it turn around more than once with engine upright? did the engine run good(no knocks) before it was pulled to eliminate rod to crank bind? give me an idea if you can see what parts bind when the engine is turned over(like when it dead ends does one of the rods stop before top dead center,usually you can see inside the spark plug hole in each cylinder when it is TDC and should be able to see if a valve cover or intake bolt dropped in when it was being dissassembled ,these are some things ive run into in the past but like i said there are soo many possibilities check these out and you can go from there
 
#14 ·
If this engine was running before you pulled it from the car and put it on the stand, then I seriously doubt it is a clearance problem stopping the engine from rotating. The suggestions that something might be hitting on the stand, or possibly the fuel pump rod stuck, seem much more likely. Since the intake manifold is off, the possibility that something was dropped down an intake port. You said you backed off the rockers - are all the valve in a fully-up position? If not, something might be caught in a partially open valve, and the valve contacting the piston. If any of the valves are down lower than the rest, that may be your culprit. If you don't find something hitting the stand, or the fuel pump rod stuck, you will most likely have to pull the heads. If you find a stuck-open valve, that should at least narrow which head to pull. Good luck.
 
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