Longblock Leakdown

[gjames]

I finished the long block assembly. However the leakdown is 20+% on cylinders 1 and 4. I backed off the valve adjustment to ensure the valves were closed and still the numbers were bad. I could see venting at the intake and exhaust valve seat. The head work consisted of cutting back the heads were the cylinder seals on the head (do to blow/burnt head gasket rings caused by low octane gas). The machinist was suppose to evaluate the valves. They were deemed ok. My guess...the valves were not, at minimum lapped in...but I doubt it. My plan now is to tear it down and send the heads out for full valve job? Any thoughts or recommendations?

[VFR750]

Which type of leakdown tester are you using?

[VFR750]

it took me many tries to lap the valves so they would seat correctly and not leak.

I made some block off plates and used compressed air and some automatic transmission fluid to test the valve sealing. I pressurized the valve from the port side and poured atf in the head. Looked for bubbles at the valve.

Took quite a bit to get the valves to completely seat.

I got very good at installing the valve spring too.

The only caution is to make sure you don’t get lapping compound on the valve stem and into the guide.

Yes, this means I’d recommend taking it appart and fixing it now. It will not get better

[boyt911sc]

Originally Posted by gjames

I finished the long block assembly. However the leakdown is 20+% on cylinders 1 and 4. I backed off the valve adjustment to ensure the valves were closed and still the numbers were bad. I could see venting at the intake and exhaust valve seat. The head work consisted of cutting back the heads were the cylinder seals on the head (do to blow/burnt head gasket rings caused by low octane gas). The machinist was suppose to evaluate the valves. They were deemed ok. My guess...the valves were not, at minimum lapped in...but I doubt it. My plan now is to tear it down and send the heads out for full valve job? Any thoughts or recommendations?

Have you heard about Anchor Atlantic Enterprises in NJ? It is owned and operated by Bob Hirst and their cylinder head works service is excellent. I was very happy with my previous machine shop and just by curiosity tried AAE for the first time more than 5 years ago. And I stayed with Bob since then. I will be sending a set of cylinder heads again this winter. Call Bob H. at this number (856)-371-6061.

Tony

[r lane]

If the heads were damaged, then I can't imagine that the valves didn't need either facing or replacing and the seats cut. Also when the heads are machined, they have to be the same on both sides as the cams can bind. Bob

[gjames]

I am using a Longacre leak down tester. I will give Bob H. a call tomorrow. All the heads were machined the same depth.

[mepstein]

Originally Posted by boyt911sc

Have you heard about Anchor Atlantic Enterprises in NJ? It is owned and operated by Bob Hirst and their cylinder head works service is excellent. I was very happy with my previous machine shop and just by curiosity tried AAE for the first time more than 5 years ago. And I stayed with Bob since then. I will be sending a set of cylinder heads again this winter. Call Bob H. at this number (856)-371-6061.

Tony

He’s been doing it forever and is known for top notch work. He stopped by our shop a while ago and is a nice guy.

[smokintr6]

Second sending them to Anchor Atlantic. My heads have always come back from there looking better than new parts!

[Trackrash]

I would be most concerned about the valve guides. Especially the exhaust. IF those are tight, a lapping may be all that is needed.

BTW, with the leak down tester installed, you can tap the valve stem with a mallet. If there is any carbon or debris present, you may be surprised as how that improves the numbers.

[al lkosmal]

I recommend Craig Garrett (CGarr on this forum) for rebuilding your heads. Excellent work.

regards,
al

[lvporschepilot]

Originally Posted by al lkosmal

I recommend Craig Garrett (CGarr on this forum) for rebuilding your heads. Excellent work.

regards,
al

Craig is the best!


I had an interesting leakdown experience with a pair of rebuilt Ferrari 355 5v heads that might be applicable. Cylinder 4 showed leak through one of the 3 intake valves, leak was 12 or 13%. Car was driven for a few hundred miles, checked odd cylinder again, 4% leakdown. This test figure was on the extremely sensitive old Snap on leak tester at 75psi. Anything below 8% with these particular units is tight. It seemed the freshly cut valves/seats just needed to break in a bit.

[gjames]

Thanks for the feedback. I am pulling the heads and reaching out to several machine shops.