We are currently running on the new domain and server: www.Speed-Talk.com

IMPORTANT: Update your bookmarks to https://www.speed-talk.com/forum/
(Right-click the URL and select "Bookmark this link")

Valve lap on boosted high mileage 5.3?

General engine tech -- Drag Racing to Circle Track

Moderator: Team

franklstoner
Member
Member
Posts: 129
Joined: Wed Feb 16, 2011 12:24 pm
Location: topeka, ks

Valve lap on boosted high mileage 5.3?

Post by franklstoner » Sun Jun 11, 2017 11:26 am

I was installing a set of pac 1218 springs on my 5.3 yesterday getting ready to install a turbo and i noticed a slight amount of air coming out the intake and exhaust ports. Since all high mileage engines valves and rings start to leak as they wear out does others still boost them. Ive havent heard to many people tearing them down just to fix the leaks before they boost it. To me i would think you would want to rebuild it but a lot of others are just installing turbos and done. Thnx

cgarb
Guru
Guru
Posts: 1758
Joined: Wed Jul 09, 2014 11:50 am
Location: Maryland

Re: Valve lap on boosted high mileage 5.3?

Post by cgarb » Sun Jun 11, 2017 1:02 pm

Could be some carbon build up or corrosion propping the valves open a bit. Sometimes just a disassemble and wire brush will take care of it. It won't hurt to try, if not then its off to the machine shop.

jake197000
Pro
Pro
Posts: 428
Joined: Sun Mar 18, 2012 11:37 pm
Location:

Re: Valve lap on boosted high mileage 5.3?

Post by jake197000 » Sun Jun 11, 2017 10:12 pm

id want everything right if i was gonna boost it.itell people not to boost half worn out engines but they do it anyway and they ussuallydont last long.pull the valves out and if the guides arnt shot you might get away with lapping them.

machinedave
Guru
Guru
Posts: 1097
Joined: Mon Mar 24, 2014 1:08 am
Location:

Re: Valve lap on boosted high mileage 5.3?

Post by machinedave » Sun Jun 11, 2017 11:00 pm

I know many people doing the high mileage 5.3-6.0l turbo setup. The heads get pulled to install head studs, I surface them and do a valve job since it has to be disassembled to swap out the springs. I am amazed at how well they seem to hold up.

mag2555
Guru
Guru
Posts: 2922
Joined: Sun Sep 18, 2011 11:31 am
Location:

Re: Valve lap on boosted high mileage 5.3?

Post by mag2555 » Mon Jun 12, 2017 6:47 am

With boost, Hell don't bother wasting time trying to lap in seats , it's a production motor that has seasoned in and shifted around! Pull the heads and get a them rebuilt.
New guides if need be and replace any valve who's stem is worn more then .001".
Any new valves needed should get checked also and since your boosting the Exh valves should get back cut applied to them.

franklstoner
Member
Member
Posts: 129
Joined: Wed Feb 16, 2011 12:24 pm
Location: topeka, ks

Re: Valve lap on boosted high mileage 5.3?

Post by franklstoner » Mon Jun 12, 2017 9:59 am

So as i understand 20% leak rate is still considered good. That you shouldn't be worried unless it starts going north of 30%. Im going by the store tonight to pick up a cylinder leak down tester. I still might pull the heads and rebuild them though.

ap72
Guru
Guru
Posts: 1638
Joined: Wed Mar 04, 2009 8:31 am
Location:

Re: Valve lap on boosted high mileage 5.3?

Post by ap72 » Mon Jun 12, 2017 10:48 am

I'd lap the valves replace the seals and run it. Keep it simple cheap and fun.
LOL, according to the post count I'm an "expert." The only thing I'm an expert at is asking questions.

mag2555
Guru
Guru
Posts: 2922
Joined: Sun Sep 18, 2011 11:31 am
Location:

Re: Valve lap on boosted high mileage 5.3?

Post by mag2555 » Mon Jun 12, 2017 2:35 pm

You have to pull the heads anyway to lap, so a quick freshen up valve job and 16 spring shims and seals is the way to go if the funds are in hand.
A leaky non sealing Intake valve with a boosted motor even on only 6 psi is not fun!

franklstoner
Member
Member
Posts: 129
Joined: Wed Feb 16, 2011 12:24 pm
Location: topeka, ks

Re: Valve lap on boosted high mileage 5.3?

Post by franklstoner » Mon Jun 12, 2017 9:12 pm

I just did a leak down on all 8 cylinders. They all average around 20%. According to the gauge their all good until 40% loss. Humm

cjperformance
HotPass
HotPass
Posts: 3585
Joined: Tue Aug 19, 2008 7:20 am
Location: South Australia

Re: Valve lap on boosted high mileage 5.3?

Post by cjperformance » Tue Jun 13, 2017 7:05 am

I have a customer with a 4.0L i6 sohc ford (2000 AU Falcon engine in a 1980 model Falcon) engine, it had done aprox 330,000km when I fitted a 7lb turbo lpg (propane/butane mix) setup for him. With this many km on the engine (which was running ok) we decided to setup and basically prove the setup, then figuring the engine would suffer, rebuild it with a few mods based around strength for more boost, not chasing big hp or rpm. Well now it has done 490,000+km , being driven daily and is actually running really well AND is actually using less oil between services than it did prior to boost! Not ideal but 'sometimes' budget stuff really does work.
Craig.

User avatar
MadBill
HotPass
HotPass
Posts: 14500
Joined: Tue Nov 15, 2005 10:41 am
Location: The Great White North

Re: Valve lap on boosted high mileage 5.3?

Post by MadBill » Tue Jan 14, 2020 10:32 pm

franklstoner wrote:
Mon Jun 12, 2017 9:12 pm
I just did a leak down on all 8 cylinders. They all average around 20%. According to the gauge their all good until 40% loss. Humm
Opinions vary, but most performance engine builders target less or much less than 10%. On the other hand, anecdotally, freshening a 15% average LD down to say 6% with a quick valve grind often yields... nothing.
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

Schurkey
HotPass
HotPass
Posts: 1470
Joined: Sun Mar 01, 2009 2:42 am
Location: The Seasonally Frozen Wastelands

Re: Valve lap on boosted high mileage 5.3?

Post by Schurkey » Wed Jan 15, 2020 12:35 am

franklstoner wrote:
Mon Jun 12, 2017 9:59 am
So as i understand 20% leak rate is still considered good. That you shouldn't be worried unless it starts going north of 30%. Im going by the store tonight to pick up a cylinder leak down tester. I still might pull the heads and rebuild them though.
franklstoner wrote:
Mon Jun 12, 2017 9:12 pm
I just did a leak down on all 8 cylinders. They all average around 20%. According to the gauge their all good until 40% loss. Humm
Raw leakdown percentage means NOTHING until you've got experience with that tester on "known-good" engines. That's the only way to know what your tester reads on "good" cylinders. Ideally, your "known-good" engine will have a similar bore size to the engine in question.

The orifice in the tester has as much influence on the indicated leakage as the actual leakage. There's no industry-standard or legal regulations on the size of the orifice. The closest we have is the FAA's regulations for aircraft engines. Frankly, what the FAA allows for aircraft is WAY too generous for a performance automobile engine. However, it's nice to use their "approved" "Under 5" bore size" orifice size and contour, which is a .040 hole with a 60 degree lead-in taper. Their diagram shows a similar exit taper, but that's not in the text of the regulation.

Some aircraft testers come with a secondary "Master Orifice", this orifice is specified by Continental Teledyne. You first run the leakdown tester into the Master Orifice, the Master Orifice produces the MAXIMUM amount of acceptable leakage. If you get a higher percentage with the engine than with the Master Orifice, the cylinder has failed the leakdown test.

Point being, YOUR tester may have a bigger or smaller orifice, with or without an inlet taper. The readings obtained with that tester apply only to that tester--they can't be reliably compared to any other automotive tester; and there's no such thing as "20% is good", or "20% is too high". Give me an hour, I can rig a tester to show whatever "percentage" you'd like to see.

peejay
Guru
Guru
Posts: 1866
Joined: Tue Aug 10, 2010 9:16 pm
Location:

Re: Valve lap on boosted high mileage 5.3?

Post by peejay » Wed Jan 15, 2020 6:24 am

mag2555 wrote:
Mon Jun 12, 2017 6:47 am
With boost, Hell don't bother wasting time trying to lap in seats , it's a production motor that has seasoned in and shifted around! Pull the heads and get a them rebuilt.
New guides if need be and replace any valve who's stem is worn more then .001".
Any new valves needed should get checked also and since your boosting the Exh valves should get back cut applied to them.
I agree 100%.

Nothing more fun than dropping a valve because it was beating itself trying to seal to an off center seat.

Plus, you're spending the time, money, and effort for a turbo setup. Doing the heads correctly is a drop in the bucket in comparison to the rest of the work and money involved, and it will bring a much better result.

BILL-C
HotPass
HotPass
Posts: 457
Joined: Thu Feb 07, 2008 9:57 pm
Location: Oakville, CT
Contact:

Re: Valve lap on boosted high mileage 5.3?

Post by BILL-C » Wed Jan 15, 2020 7:27 am

The LS engine platform is definately impressive. Like everything else, it does eventually wear out and need to be freshened up. Sometimes it seems like there is an informal contest in the internet backyard LS builder crowd to see who can be the biggest cheapskate and build the worst pile of worn out parts that will run. Do the job right and take some pride in your workmanship.Do a valve job and get the heads resurfaced.
Carlquist Competition Engines

1980RS
New Member
New Member
Posts: 25
Joined: Thu Oct 13, 2016 10:03 am
Location:

Re: Valve lap on boosted high mileage 5.3?

Post by 1980RS » Wed Jan 15, 2020 9:13 pm

I had a set of SBC 5.7 Vortec heads I am using for a 406 project that had only 40K on them and the seats and valves were really pitted on the exhaust side, not so much on the intakes so you cannot count on having great looking seats and valves with a ton of miles on them. I cannot believe the 5.3's would be any difference. I would never waste my time on lapping something with high miles as like others have said, you have to take the heads off either way. Are you building a performance engine or a daily driver? either way do a good valve job on both and your engine will thank you for it.

Post Reply