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-   -   SB Chevy that will only turn 1 revolution... (http://www.hotrodders.com/forum/sb-chevy-will-only-turn-1-revolution-227067.html)

sunrise7 12-11-2012 01:31 PM

SB Chevy that will only turn 1 revolution...
 
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....

engineczar 12-11-2012 01:46 PM

What size engine? New build or old?

If new and it's a 383 then you probably have a rod hitting a lobe on the cam.

kentactic 12-11-2012 02:47 PM

Quote:

Originally Posted by engineczar (Post 1621644)
What size engine? New build or old?

If new and it's a 383 then you probably have a rod hitting a lobe on the cam.

How does a rod hit a lobe on the cam? You mean rod hitting the bottom of the cylinder wall?

Im wondering if im going to need to clearance for the rods in my 383.

engineczar 12-11-2012 02:57 PM

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.

kentactic 12-11-2012 03:29 PM

Ah i see. and yeah i meant clearance the cylinder not cut the rod itself. Is it typical to have to do this on a 383? Or should i assemble it first to see if its an issue?

Sorry dont mean to rob this gentlemens thread.

Trucknut 12-11-2012 03:40 PM

I had that problem on my Pontiac 400. The dipstick was winding around the crankshaft because the builder didn't put in the lower dipstick tube.

sunrise7 12-11-2012 04:00 PM

Its a stroker.... but it ran before we pulled it out of the car it was in.

Hans2 12-11-2012 04:27 PM

Quote:

Originally Posted by sunrise7 (Post 1621640)
I have a small block Chevy engine that is currently mounted on my engine stand.

Taking a flyer here - Any chance the counterweight on the back of the crank is hitting the mounting bracket for the stand?

bowtiemike 12-11-2012 04:27 PM

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

engineczar 12-11-2012 04:32 PM

Just throwing this out there. Any chance something is hitting the engine stand like a bolt in the flange of the crank?


Edit: Hans beat me to it.

BogiesAnnex1 12-11-2012 04:38 PM

Quote:

Originally Posted by kentactic (Post 1621668)
Ah i see. and yeah i meant clearance the cylinder not cut the rod itself. Is it typical to have to do this on a 383? Or should i assemble it first to see if its an issue?

Sorry dont mean to rob this gentlemens thread.

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

kentactic 12-11-2012 05:53 PM

Quote:

Originally Posted by oldbogie (Post 1621709)
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

Thats the rod im working with, im assuming this is the cap screw style you recommend? Its a 5.7''. Next if i can count on the cam making contact then what style cam should i be looking for? This is the total Rotating Assembly i have: http://www.kmjent.com/cart/assault-p...-assembly.html

http://i5.photobucket.com/albums/y16...-05_124618.jpg

BogiesAnnex1 12-11-2012 06:39 PM

Quote:

Originally Posted by kentactic (Post 1621725)
Thats the rod im working with, im assuming this is the cap screw style you recommend? Its a 5.7''. Next if i can count on the cam making contact then what style cam should i be looking for? This is the total Rotating Assembly i have: Assault Pro Series 383 Balanced Rotating Assembly - KMJ Performance

http://i5.photobucket.com/albums/y16...-05_124618.jpg

That would be it. These usually don't have clearance problems, but things are tight and manufacturing tolerances result in slight differences, so the next step is to put the cam in then the crank then install the piston and rod assemblies and timing set. Then run the damper bolt in to use it with a wrench to rotate the crank in the clockwise direction from the front, easier done with a friend slowly turning and you spotting with a strong light and a set of feeler gauges to measure the clearances as the crank is turned.

The only time this stuff just assembles by stuffing parts in is on the OEM assembly line where the clearances are designed in so assembly is production line fast (what they call “rate” in the factory) and always repeatable one engine to the next. When you strike out building hot rod engines every engine, even what appears to be copies with the same parts, are custom builds requiring that all these contact points be identified and checked. Expect to have the engine assembled and checked then disassembled and reassembled then maybe rechecked at least a couple times before it finally goes together. A stroker needs this bottom end checked out, include in that the oil pump clearances to crank and bottom of the pan. Windage tray and scrapers to crank and oil pump if these are used. Fit of the distributor to the cam gear and oil pump drive this means you need to put the top end on with the pan off. But At this time you can also check the piston crown to deck clearance sometimes you find the pistons are rebuilder high pin type and the zero deck you thought you had is back to oh-twenty five and the compression gone to hell with it, and by the way the wrong pistons were in the box marked for a standard height pin piston ( oh-well S#it Happens). Or you discover that milled heads and decked block with the high lift cam and or high ratio rockers have the valves and pistons occupying the same space at the same time. This is all a PIA to check out but is lot easier and cheaper to fix before building a fire in the cylinders then discovering the things that don't clear each other.

Bogie

sedanbob 12-11-2012 08:34 PM

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.

sunrise7 12-15-2012 11:26 PM

Thanks guys. Lots of things to check, but not much time this week. I do know for sure that its not a bolt in the crank flange or any interference with the engine stand. The engine has been sitting for a couple of years,, so maybe some rust up high in one of the bores where the piston is near tdc when it stops turning.... Guess I will have to pull the heads to find out for sure.... I highly doubt its interference with the cam since this motor ran before we pulled it out of the car..... :P


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