LT5 Assembly Project

[LGAFF]

Bob if you want to stop by that would be great to get your thoughts....I need to get the cams in yet.


Jerry we should be good to go on the valve guides and seals, I had the cams in the heads and rotated them so any clearance issues should have been evident at this point..thus the need to replace the damages exhaust seals.

[A26B]

Originally Posted by LGAFF

Jerry we should be good to go on the valve guides and seals, I had the cams in the heads and rotated them so any clearance issues should have been evident at this point..thus the need to replace the damages exhaust seals.

I hope it was all check measured and inspected before assembly with springs. You could have spring retainer cap contact with the seal & never feel interference by rotating the cams unless the guide was so high it caused a hard bind. It takes a lot of torque to turn a single cam against 8 valves.

How much lifter compression did you end up with on a fully extended lifter?

[LGAFF]

Leakdown test:

Cyl-%
1-22%(Exhaust valve leak)
2-8%
3-12%
4-14%
5-31%(piston rings)
6-10%
7-35%(exhaust valve seat/piston rings not sealing)
8-5%

[LGAFF]

Some question as to whether the 120ftlbs of torque on the head bolts might play a factor in the valve seating....

Looks like I will be pulling pistons 5/7 out and checking bore

Also will revisit valve seals on 1/5/7

[XfireZ51]

Xrist, wtf is going on?

Originally Posted by LGAFF

Leakdown test:

Cyl-%
1-22%(Exhaust valve leak)
2-8%
3-12%
4-14%
5-31%(piston rings)
6-10%
7-35%(exhaust valve seat/piston rings not sealing)
8-5%

[LGAFF]

Spoke to one of the Mercury guys about leakdown on new motors, response is below...


The leakdown spec's we went by were 14 to 18% on green engines broke in were lower we did have some engines that were higher but only about 20 to 24 % anything higher there was a problem that need addressed. I take it this isn't a stock LT-5

[LGAFF]

Pulled the D/S head today, but before doing that backed the head bolts down to 65ftlbs.....and exhaust valve leaks were 1/4 of what it was at 118ftlbs....

Will check the bores on 5/7 to see why the rings are not sealing

[Paul Workman]

Originally Posted by LGAFF

Pulled the D/S head today, but before doing that backed the head bolts down to 65ftlbs.....and exhaust valve leaks were 1/4 of what it was at 118ftlbs....

Will check the bores on 5/7 to see why the rings are not sealing

If I read it right, except for the bores with rings leaking, you may be close to being done. However, the valve leak-down changing with head bolt torque comes as a surprise! It crosses my mind (as I'm sure it does yours too) that something isn't quite right, but not sure where to start on an open deck. Keeping in mind that it is still w/in the exception mentioned by the Merc guy, I guess I'd want to check some basic stuff anyway...

Since you're going to have that head of anyway (to check on the ring situation) I guess I'd have Al lay his straight-edge across the top of the block to make sure there isn't an issue there. And, I'd want to re-mic' the sleeves to make sure that none are too proud (or sunken either). And, while Al has his straight edge out, lay it across the head too. (Were either of these heads decked already??).

As for the rings, I assume the two in question are gapped correctly, yes? I guess I'd want to verify the fundamental stuff with an SOP measurement of the bores: do you have a spare ring or two you could use as a makeshift gauge to check the bores for some anomaly? Putting a ring into the empty cylinder and by placing a light source behind the ring, look for light peaking from under the edge of the ring - along the entire length of the stroke. If there is light somewhere, rotate the ring to be sure it is the bore and not an anomaly with the ring "gauge". I'd be curious too to see if the gap remained the same, i.e., in spec for the length of the bore as well. If that doesn't "shed any light" on the subject, then for sure I'd want to swap the rings on the offending pistons - with one of those rings that proved out also as a gauge - before going further.

Further? No more arrows in my quiver. Bob G or Marc or Pete might have further/different checks to make.

I'll shut up now and go back to lurking now.

P.

[XfireZ51]

Paul,

I had similar thought regarding height of barrels after having watched Bob and Pete do their thing a few weeks ago. I can imagine if that isn't right it would be affected by head bolt torque and show up as uneven cylinder pressure.

[LGAFF]

-Bob G has been helping me out, we are checking the roundness of the liners, possible they are not round and with new rings not seating.

As for the heads its been seen before, when you torque something 118ftlbs sht happens....and as you can see from the comments from the foreman at Mercury up to 24% leakdown was not out of the question

Rings came from the factory with acceptable spec on the gap, I am using a tighter gap than factory