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Leak down test

mvalenti

mvalenti

Forum Mentor
So i have a compression tester that i checked my engine with. I got numbers in the range of 105-120psi. I now want to do a leakdown test. I rigged up some fittings on my compression tester to adapt to my air supply. How much pressure should i introduce? For how long? Should i loosen the oil cap so not to pressurize the crank case in case of a bad ring ?
 
Set the engine at Top-Dead-Center and attach the leak down tester hose to the spark plug hole. Lock the crankshaft in place. The tester is attached to an air supply and set at 100 psi (Pounds per square inch). You then connect the tester to the tester hose and read how much air is leaking out of the cylinder.

If the engine is in the frame you can put it in gear and apply the rear brake. If the engine is on the bench, things are a bit harder. Now you have to lock that engine. If you use a wrench on the crankshaft bolt be sure to use a long one with lots of leverage. If you used a regular sized wrench you will find that the 100 psi of air pressure will apply a tremendous amount of twisting pressure to that wrench.
 
If you just want to find out where your leaking is taking place, you can use a lower pressure than 100psi. If you do use 100, like he said, make SURE you can secure the crank.
 
Thanks all! If I get leaking past the rings and the crank case see's pressure, should I remove the oil fill cap?
 
Your crankcase is already vented into the air box so there's no need to remove the oil filler cap; however you may want remove it in order to listen for air leakage into the crankcase. ;)
 
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I feel like an idiot... I sooo knew that... Uggg....

So if'n i need to rebuild the top end, valves, guides, hone, rering.. Any thoughts to online stores for pArts?
 
Could possibly need rings then.

What I do is keep an eye on Ebay looking for OEM base and head gaskets that can be purchased on the cheap, then I order all the necessary o-rings (stud-base-chain tunnel) through an online dealer. Or you can watch for a complete engine set as they do come up from time to time for sale. Rings do come up for sale as well.

Posting in the parts wanted section may bring up a reasonably priced head gasket as well.
 
Thanks for the info, i did a quick search on ebay. They have a set listed that seems sketchy... Brand new not old stock...
THESE RINGS ARE THE STANDARD SIZE FIT

FOR ALL MODELS OF THE 1978 TO 1981 GS1000

THESE RINGS ARE ALSO THE CORRECT FIT 1.0mm OVERSIZE

FOR ALL MODELS OF THE GS850

REPLACES SUZUKI PART NUMBER: 12140-49001

Fits both 850 and 1000?
 
An '850 bored 1.0mm oversize and the STD bore '1000 use the same rings.
 
You may want ask Jeff at Z1 his opinion on what he thinks of the quality of the gasket sets he sells. (I suspect if he sells it it's favourable.)

http://www.z1enterprises.com/ItemDe...t+Set+GS850+(79-81)+Complete+Set&item=MAGK440

NOTE! That kit contains a 72mm head gasket.

Worse comes to worst you can always substitute an OEM base gasket in place of the one that comes in the kit. http://www.ebay.com/itm/380608758961?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649 ($9.52 @ Boulevard)

Just something else to consider.
 
Sweet.... I was really hoping to just hone and re-ring and not have to bore, just a PIA... Really want stock or .010 rings max..... I do have a full machine shop at my disposal, but really dont want to spend a weekend setting up and boring the head... Thanks again for all the help..
 
Or your could score a low mileage set of cylinders complete with pistons and rings off Ebay.

(have an 80 '850 cylinder head on the shelf at home)
 
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