cylinder leakdown results

[skostur79]

i performed a leakdown before tearing down my engine

at tdc i have any where from 60% to 72% leak down seems kinda high,,
at bdc i have 14% to 30%

no 1 cylinder showing the highest

let me add that there were no running problems , coolant usage , etccc the engine was rebuilt once (.010 under on crank , cylinders have not measured yet)

i did note air leaking a ehxaust ports and crankcase areas

the heads are getting checked and if ok a vjob and new springs will be done

but should i just pop some rings in and hone the cylinders while i got them off?

your thoughts because this is my first turbo engine rebuild

 

[Jerryl]

....... at tdc i have any where from 60% to 72% leak down seems kinda high, .......... at bdc i have 14% to 30%

let me add that there were no running problems , coolant usage , etccc the engine was rebuilt once (.010 under on crank , cylinders have not measured yet)

i did note air leaking a ehxaust ports and crankcase areas

Sounds to me like there is cylinder. The upper part of the cylinder is larger in diameter from the wear. Depending on the amount of wear, you may not get the correct piston to wall clearance and the cylinders probably need to be bored out.

IMHO, you want to shoot for around 3-5% leakage. Depending on your goals and budget you may decide to just deglaze the walls and put some new rings in ….. or bore the motor and install some good pistons, and have the motor balanced.

As far as the leakage past the exhausts ..... sounds like you caught it in time and you are taking care of it. It is a fast way to burn a valve and ruin a bit more than just the valve or head. The crankcase leakage you are hearing is the leakage past the rings.

 

[VadersV6]

This is not something a ball hone will fix. Its got to be done right. If you're getting alot more leakage at TDC, you have alot of cylinder taper and the rings have probably worn a decent step in the upper part of the cylinder. If you dont remove that step and throw in new rings, the new rings will be destroyed in the time it takes to fire the motor up. The top of the step has a rounded edge. You run a new ring with a sharp edge into that rounded edge, that ring gets smashed and will either crack or just generally crush the edge of the ring. Now you have ring debris floating around in the cylinder, trashing everything. A ball hone wont remove that step. It has to be completely removed with an overbore and a good hone. People seem to never have the time or money to do it right the first time, but somehow come up with the money and time it takes to fix it later. Just pull the motor and get a quality rebuild. I would highly recommend a square decking (this can fix several issues that are hard to figure out), a torque plate hone (this is more important than many recognize...your rings will last 3 times longer and seal much better)), and a good line hone. Throw on a main girdle while you're at it. The girdle is cheap and is great insurance. Make sure the line hone is done WITH the girdle on the motor. I would get it balanced and have them drill out the oil return passages, and radius the edges of those passages. You dont want all your oil accumulating to the upper end of the motor and have the oil pickup get dry at 6000rpm. Its not necessary, but I would really stress it, especially if you get a high volume pump. As far as the heads go, if you dont want to port them, at least have them do a 3 angle back cut on the valves. This increases low lift flow quite a bit. Make them cut the 45 on the valves to a 44.5 degree cut. The seats will still get cut at a 45. The valves will break in better than you can imagine, and wont burn or leak. A 45 against a 45 seals like CRAP. Make sure all the valve stem heights are the same when they're finished. Bring a ruler with you to the shop and lay it across the tops of all the valve stems. This is important.