East Coast B

What are the procedures for performing a leakdown and compression test? What instruments are needed and cost of these?

mobilecal

I dont know what the time limit is, but the only way I know how to do a leak down test is by removing the spark plugs and rolling the crank on its compression lift, holding it there for x number of minutes to check the seat of the valves and the seat of the rings... This is done with a gauge in place of the spark plug. Do this eight times.

Am I close guys to marine applications??

articfriends

my blown 502 i ran 185 hours which was anout 30 hours too long,it was burning oil and leaking oil bad towards the end. my 540 had pretty good leakdown results(under 10 %) at 90 hours but at 138 hours had several cylinders at 35% and one at 70%. The boat still ran good but was starting to puff a little oil when i started it up. It had also lost 1 1/2 mph at wot. The bearings looked like new but valve job was shot,head gaskets were almost burned thru wire ring.timing chain had chips in the rollers and the cylinder that had 70% leakdown had a intake valve that was sawing thru the guide.If I had tryed to run it a 3rd season it would have blown up in middle of boating season. A normally aspirated stock motor would be a whole different story,I would do a leakdown annually and watch oil pressure,when it started to lose cylinder seal it would come apart at that pont other wise i would just watch to make sure it didn't smoke on start up,tick or lose power,Smitty.
P.S.-I bought a leakdown tester at local carquest for 50$,you need to roll cyl on tdc with plugs out,screw gauge in,adjust regulator to set gauge at 0 and open valve and watch gauge,its simple,it just takes a little time.

mobilecal

So 200 hours would have been fine for you if you had a NA motor...Did you build the motor yourself?

articfriends

Yes,i built both motors myself. When i built the 502 i had the block honed on a torque plate and replaced the j/e original pistons that use low tension metric rings that are touchy and prone to leakage with new j/e's that have std rings. I used j/e plasma moly rings on that motor,at teardown they were real beveled and wore looking causing the high leakdown and blowby. When i built the 540 i had it plateau honed with a torque plate and used zero gap rings,i am confidant the high leakdown numbers it had were caused by the valve train,if i didn't find the tiiming chain rollers starting to chip slightly its possible i could have freshened just the top end as the rings looked very good. The comp cams hydraulic roller lifters also looked like garbage too though.This time when i built the 540 i used new pistons identical to last time but i sent them to swain tech and had the skirts and crowns coated for insurance against scuffing and heat transfering thru the crown. The old 540 pistons were slightly scuffed but showed sighns of heat on backside so i didn't chanch running them. I may run this 2 years this time and do the top end only. Here is a pic of the piston coatings. If this was a n/a motor it would easily go 400 hours as it has top of the line parts in it,Smitty

mobilecal

what did the coating cost you?/

was the torque plate something you made or ordered. I was just wondering what the tolerances were on the plate's. Did you achieve the .0002 with your plate?

articfriends

The coatings cost 58$ per piston plus s/h there and back(roughly 500$) I also sent the cylinder heads to swain tech and had chambers and exhaust runners coated(another500$). The local machine shop has a bbc torque plate and modern hone,the cyllinders were less than .0005 out of round but remember if your measuring them at home after having honed w/torque plate they won't be as round as when they were w/plate on. I mainly look at piston to wall clearence,not roundness after having cyl honed w/plate,Smitty

mobilecal

Ive never installed the zero gap rings before, is there a technique to installing them. They cant be as easy as your gapped rings.


Also did the machine shop give you the torque sequence in attaching and removing the plate?

Did they use their bolts or yours?

articfriends

Zero gap rings are ALOT of work to install but they provide great ringseal. It is a tedious slow process gapping each piece,lining them up etc. I also use ring sealing compound,another messy,slow process. As far as torque plate and torque sequence the shop used their bolts,would have probably been better to have them use my studs but probably not too critical. My heads are aluminum and of course their torque plate is steel so there might be some small differences there beyond my control that would be more signifigant than using the studs vs bolts.If you wanted to get real carried away you could build a torque plate that mimiceked a aluminum head out of billet aluminum and use the studs,at that point you might as well circulate warm water thru the block at same temp motor runs at too .I torqued heads from middle out as detailed in old chiltons,Smitty

gripit

Whats the difference between a compression test and leakdown test?