Resistance when turning over engine.

[TheMechanic253]

Hello all!

I recently finished putting together my rotating assembly of my 7mgte.

I used stock rods which were resized with ARP rod bolts torqued to 50ftlbs. All my clearances were within .0015-.002 (Toyota says .0008-.0021)

I used stock pistons with new rings and the cylinders were honed.

My crank was polished and balanced. I used stock main bolts torqued to 75 ftlbs. I used new Clevite bearings with plenty of moly assembly lube.

I installed my rings with some WD40 and in the cylinders.

The head is not installed yet.

MY QUESTION.

When turning the engine over with a torque wrench, there are a few places where the engine takes 20ftlbs to turn over and other places its much less. The engine seems to turn by itself after the resistance. I only have experience building 4 bangers and I was wondering if this resistance is normal. I know that the 7m is a picky engine and I want to make it last for as long as possible.

Any advice, comments welcome.

 

[IJ.]

Did you have the block checked for straight main tunnels?

Crank checked for straightness?

 

[TheMechanic253]

I had a machinist check everything out and when I picked up the parts he said everything was ready to assemble.

He balanced the crank. He told me that he has machined over a dozen 7m's. This guy is pretty sharp. Everyone that works in the shop has over 15 years experience. I plasti-gauged my mains also. I forget what they came out to, but I know it was within tolerance.

 

[TheMechanic253]

But he did not specifically check the main tunnels that I know of. or specifically check the crank for straightness.. but I don't know how it could be, bent?

 

[Nick M]

Did you have the block checked for straight main tunnels?

Crank checked for straightness?

Right here.

Is the torque wrench resisting at the same point in every rotation? Besides the crank, don't forget the piston clearance.

 

[TheMechanic253]

I thought it might have something to do with the angularity of the crank as the rod is changing direction. Yes it happens 3 times during each 360* rotation.

I can't imagine how the block would not be straight.. ?

My pistons are OEM and the cylinders have been honed so I know that the PTW is looser than Toyota originally had.

 

[Suprapowaz!(2)]

I thought it might have something to do with the angularity of the crank as the rod is changing direction. Yes it happens 3 times during each 360* rotation.

Could be. Why did the engine need a rebuild in the first place?

 

[IJ.]

I-6 is a long wet noodle.... You'd be surprised at how much they flex under power, after awhile they take a set so it's important to check the tunnels, I bought a brand new block and still checked it..
But if it's doing it at 3points in it's rotation it might be as you suspect, would be worth marking the damper to see if it's at 120 degrees each time, at a bare minimum I'd be pulling the caps and checking the bearings for rub marks..

 

[TheMechanic253]

When I got the car, the previous owner had rebuilt the engine and he put a head on that was cracked. When he started it, coolant was blowing out of the exhaust.

has anyone ever used a torque wrench to turn over their engine? Mine is one of the old ones with the needle that moves when you pull on it.

Did the engine that you all have built turn over with the same resistance 360* rotation by hand?

 

[Nick M]

has anyone ever used a torque wrench to turn over their engine? Mine is one of the old ones with the needle that moves when you pull on it.

Did the engine that you all have built turn over with the same resistance 360* rotation by hand?

After a rebuild, yes. After the fact, no. If there is an engine problem, it will show up as soon as the engine is running.

 

[TheMechanic253]

After the fact meaning after you started it?

And "will show up" means spinning a bearing right? haha

 

[Suprapowaz!(2)]

I just thought of something. What did you set your ring end gap to? Maybe they're too tight and cause a damn good seal, so when you turn the engine over the compression give you stronger resistance than normal. Just a thought.

TSRM say No.1 ring set between 0.29-0.44mm. No.2 ring 0.25-0.53mm. Oil ring 0.10-0.44mm.
What did you spec yours out to?

 

[TheMechanic253]

Well I measured by thousandths of an inch with feeler gauges. I did not file them at all I just measured them in the honed bore of my block. starting with top ring, going down

Also my cylinder head is not on yet, so there is only resistance, no compression. I plan on removing one rod at a time and turning the engine over until it stops, then checking that assembly. I think I really should gap the rings evenly...

Such lack of motivation right now.

Piston 1 .022-.022-.024
Piston 2 .020-.024-.025
Piston 3 .020-.022-.022
Piston 4 .024-.022-.024
Piston 5 .018-.020-.022
Piston 6 .028-.024-.025