11 replies to this topic

[Karim]

Hi guys,

 

A bit of a head scratcher here.

 

I went to see a friend who has a 7 bolt 4g63 for sale. The cylinders are overbored slightly. Head gasket is a cosmic metal gasket.

All bolts/studs are ARP. Timing belt was done recently. We checked the timing and it is correct.

 

The engine is out of the car. Intake and exhaust manifolds are off.

 

We tried to do a compression test on it.

 

- Removed all spark plugs

- screw in the compression tester gauge

- Used a battery to power the starter, jump the starter solenoid

 

The engine turns over but won't give any more than 60-70 psi on all 4.

 

The owner is 100% certain the engine was running fine when he pulled it out of the car.

 

What are we doing wrong? I highly doubt and engine with 60-70 psi would "run fine".

 

We are both baffled.

 

Any ideas?

 

Thanks in advance.

[Benzo4gT]

Did you put a bit of oil into the cylinder before testing(wet test)?  How fast was it winding over?

[Karim]

We did try both dry and wet. No difference.

 

Winding over pretty fast. We used a good battery from a running car.

[Karim]

I am starting to think the compression tester is not good.

[jack be nimble]

If its same wet and dry, it should be ok. But it is a strange one.

Maybe try tester on another car. Or the mower.

I cant imagine that there are funny pistons in it that are giving it 6:1 compression.

[MDK87]

If you've double checked the camshaft timing and you've got the manifolds off it should be easy to do a leak down test to determine if your valve seats are any good.

If the above checks out ok and you're losing pressure, provided the engine is still sealed, check the dipstick tube for air escaping past the rings.

[leadfoot]

a wet compression test would have indicated if there was a ring issue

[Karim]

Checked the tester on another engine. Tester works fine.

 

Something wrong with the engine.

 

Thanks all!

[jack be nimble]

So now you need to do leakdown test, or even borescope.
I normally use leakdown on a engine not installed.

[poirier4]

lol funny to find this thread why googling

Ok well my engine was running great, 94octane tuned 780pte injectors, walboro 255lph, ecmlink, dual stage selectable greddy boost control set to 18 and 23psi, screamer elbow, had all wideband o2 egt, oil pres/temp, water temp etc, new throttlebody fiac valve, 18g wheel on evo 3 big, engine had 35000km on it

Never had problems starting it, took it out because the guy who sold me the car wanted engine back for a good price theb choked, been sitting in my garage for 4-5 months, never took oil

Engine i didnt build came with the car has

Rebuilt head all oem with 3 angle valve grind

Arp head, crank, rod studs, cosmic head gasket, overbore cylinder 0.20 i believe, acl race bearings, balancer shaft removal kit

Now 70psi on all 4 cylinders is weird but engine was running good no idle problem so i have no idea... Imma run the engine this weekend and redo the compression test

[Karim]

Hey Shawn,

 

My guess is the compression will go up once you run it a bit. Probably stuck rings.

Are you putting it back in the white car?

[jack be nimble]

Hope it comes up good. Sounds like a great little engine.
Would be interesting to know what pistons were used for the +20 overbore.