Compression Readings

[John_S]

Before winterizing, I decided to check compression, just in case there was a problem would work on it over the winter. The readings seem a little high (compared to expected 150-160) but close to calculated (172-see below), but fairly certain there isn't a large carbon build-up. The vortec heads are new this spring, there was only light carbon on pistons (spring), and plugs did not show carbon.

185 - 8 | 7 - 180
178 - 6 | 5 - 178
180 - 4 | 3 - 178
185 - 2 | 1 - 185

Was performed with engine hot and dry method. 5 revolutions per test. All plugs removed and Q-jet wide open including air door. Ignition grounded.

Compression gauge is a new Sears Craftsman kit. Not a bad DIYer kit, BTW. It has a hose attachments with plug fittings, that were easy to install around exhaust manifolds. Then the gauge with hose attaches via a quick release (air compressor like) attachment. It looks to be made by the same company as Actron gauges, which were $20 cheaper. The storage box and extra fittings seemed worth it. Much better than old real cheapo thats been at the bottom of the toolbox for 20 years.

Calculated Static Compression Ratio: 8.8:1
Calculated Dynamic Compression Ratio: 8.6:1
Calculated PSI 8.6 X 20 = 172PSI

A little concerned about plugs, put they didn't have lots of hours on them. The inner four cylinders (3,4,5,6) were fairly white, and the outter light tan or tan. Maybe a small leak on both exhaust risers? I fogged the engine, and complete drain down, but didn't add antoifreeze yet, in case I decide to pull manifolds.

vacuum at 17 @ 600rpms and steady - same as spring readings

 

[180shabah]

Re: Compression Readings

(compared to expected 150-160)

Was 150-160 based on previous readings in this engine?

Those numbers (178-185) are the exact same as the readings of my 4.3, book says they should be 180.

 

[John_S]

Re: Compression Readings

No, my old gauge was too short and could not get around the manifolds. The expected (150) was from a SB service manual.

In the spring, after I start and burn off the fogging oil, will run some seafoam through and redo the comp test. I doubt if it changes it, but simple to do.

 

[Benny1963]

Re: Compression Readings

those numbers are good should be strong decent idleing motor
plugs sound like could just be gas related timing issue
may do a good valve adjust whan you pull it back out to run it .
b1963

 

[Robj]

Re: Compression Readings

Based on other posts that I have read, I would not run Seafoam through a 4 cycle engine. Your nos look good, I would not worry about it.

Have a great day.

Rob.

 

[wallydc2]

Re: Compression Readings

Why would'nt you run sea foam through a 4 cylinder engine?

 

[180shabah]

Re: Compression Readings

Based on other posts that I have read, I would not run Seafoam through a 4 cycle engine.

Why not?

 

[Robj]

Re: Compression Readings

I have read other posts in this forum that recommended not to. Apparently that stuff is for 2 cycle engines not 4. Some clain to have experienced problems with it, however some of those problem may have been there originally.

Have a great day,

Rob.

 

[180shabah]

Re: Compression Readings

Other way around. In a 2 cycle your parts are lubricated by the oil in the gas. When you add a solvent to the gas, all of the oil gets washed off. No lubrication.

4 cycle has a dedicated lubrication system.

 

[JustJason]

Re: Compression Readings

i've heard (but have not seen) issues with seafoam blowing down past the rings and thinning the oil like crazy.
If your going to use seafoam i'd highy recomend changing the engine oil right after....
an alternative, and this is what i use. Is yamaha's cumbustion chamber cleaner. Smells like cat p!ss... but certainly does the trick. never had any kind of issue in a 2 or 4 stroke with this product, and it's specified for both.

 

[John_S]

Re: Compression Readings

I have heard its cheaper to mist water on a 4stroke, but never heard that seafoam caused problems with them I use it on my outboards and lawnmower engines as part of the spring maint. I do change my oil after.

 

[Robj]

Re: Compression Readings

Sorry but I did have it the right way. I would not use the stuff on my 4 cycle. If you want to, go ahead.

Have a great day.

Rob.

 

[John_S]

Re: Compression Readings

I am fairly certain that the can indicates it can be used on both. Can you point me to the issues/problem posts? Thanks.

 

[180shabah]

Re: Compression Readings

i've heard (but have not seen) issues with seafoam blowing down past the rings and thinning the oil like crazy.

Where did you HEAR this, how many gallons of seafoam did they suposedly use, did they pour it into a nonrunnung engine and let it sit for days, and what made you believe it?

....an alternative, and this is what i use. Is yamaha's cumbustion chamber cleaner...

The Yamaha Magic Solvent somehow knows that it has to stay on top of the rings? Maybe the Seafoam knows too, but just has trouble following orders.

 

[Robj]

Re: Compression Readings

180shabah you can put whatever you want into your engine for all I care. But you do not have to knock someone because they don't agree with you, we are entitled to our own opinion. Capt uses his own stuff, and I choose not to use your magic seafoam in my 4 cycle engine. Yes there are posts on this topic, and as always there are differing opinions. Would I use it in my 2 cycle, you bet. Have never used any of that stuff in my cars and I will not use it in my inboard.

Have a great day,

Rob.

 

[John_S]

Re: Compression Readings

Rob,

If you have links to the posts, I would like to take the time to read them, and understand their point of view. Searching on "Seafoam" brings up way too many posts to read. Thanks.