Spec'd compression value Briggs 18hp twin - 422707 [Archive] - MyTractorForum.com - The Friendliest Tractor Forum and Best Place for Tractor Information

: Spec'd compression value Briggs 18hp twin - 422707


khnitz
08-05-2008, 12:37 PM
I have more detail posted in another thread on my struggles with this motor, but I'm looking for a clear answer on this - what compression value is specified for the 18hp Briggs twins? - this is model 422707.

I went to engine(s) last night and took some compression measurements.

Engine1 (the one I most recently put into the JD 116) - cyl.1 = 50psi, cyl.2 = 75psi.

Engine2 (the spare) - cyl.1 = 65psi, cyl.2 = 70psi

I should have checked this before I installed the engine. What is the expected value for these motors? All these values seem a little low to me.

From reading other threads, verifying that the valves aren't leaking are also key to the compression reading. I'll be checking on that in the near future.

DLF_IN
08-05-2008, 02:07 PM
I don't think that Briggs ever put the compression values out. They do, however, recommend a leakdown test to check an engine for any problems. The only compression check refered to in my Briggs manuals is to spin the flywheel backward quickly. If it rebounds, the compression is good enough for the engine to run. :goodl:
Dave

khnitz
08-05-2008, 03:37 PM
Thanks for the info. No published compression values...well, that should make this more difficult...:Stop:

I guess I'll try the backup motor next, and then go from there.

Anyone ever measured a known good motor? What values did you see?

Walt 2002
08-05-2008, 04:16 PM
While B&S doesn't post compression figures, I would expect min. around 100lbs.

Walt Conner

khnitz
08-05-2008, 09:56 PM
A good 12hp B&S single I checked tonight showed 75psi. Hmmm...

Termy
08-06-2008, 04:06 AM
Small engines have compression releases which do function properly if the valves are adjusted to spec. So its normal for a engine compression test to show 60 to 90 PSI cause the compression release kicks in untill the engine is running and then the engine will be doing around 200 or more PSI, thats a proper running engine of course. If you actually have a leak, then your compression will be considerable less and not enough compression to keep running.

Bill Kapaun
08-06-2008, 09:21 PM
Small engines have compression releases which do function properly if the valves are adjusted to spec. So its normal for a engine compression test to show 60 to 90 PSI cause the compression release kicks in untill the engine is running and then the engine will be doing around 200 or more PSI, thats a proper running engine of course. If you actually have a leak, then your compression will be considerable less and not enough compression to keep running.

200 or more PSI?
That's about 14:1 compression/ I don't think so-

khnitz
08-06-2008, 09:53 PM
Nice to see that with the compression releases, you can actually get a true compression value unless the engine is running...which is darn near impossible :-O

So it's a little hit or miss between the two motors I have at the moment. I guess I'll get the second one ready to swap in and see what happens.

khnitz
12-01-2008, 02:13 PM
Well, I skipped the second and went to a third motor I found locally. That one runs, but died at higher RPMs. I'm also thinking I may have a bad ignition switch on this mower, too...it doesn't always kick right over in start - either a bad ignition switch or kill sensor on the brake pedal, transmission lever, etc.

I took apart the original bad motor over the long weekend. Turns out that one of the crankshafts disitegrated, taking out most of the rest of the internals of the motor.

So, over the winter, I'll have to piece one of these 3 possible donor motors together to get a running setup. Oh, and the throttle cable sprung loose from its retainer and stretched the "spring" sleeving. yeesh. :Disgus:

joshockey
01-23-2011, 05:53 PM
not that im any help but i have an 82 craftsman with a 16 hp its original with low hrs and im getting about 60lbs per cylinder i know a guy here who deals in briggs and has been in business for 30is yrs and said that those were satisfactory. ive always been told as long as both cylinders were close in ratio then you dont have too much to worry about. i do have a good 18hp that i need to get readings off of and for me to even use this motor i have to switch my sump over and intake etc since its a horizontal not vertical.

larrybl
01-23-2011, 06:08 PM
Quoted from the Briggs repair manual....

Check Compression
Briggs & Stratton does not publish any compression
pressures, as it is extremely difficult to obtain an
accurate reading without special equipment.
It has been determined through testing, a simple and
accurate indication of compression can be made as
follows:
Remove both spark plugs and insert a compression
gauge into either cylinder (one cylinder at a time). Turn
engine over with engine starter until there is no further
increase in pressure. Record this reading. Repeat
procedure on other cylinder and record that reading.
The difference between both cylinders should not
exceed 25%. More than 25% indicates loss of compression
in the cylinder with lower pressure. See example.
Example:
Cyl. #1 Cyl. #2 Diff. % Diff.
Eng. #1 65 PSI 60 PSI 5 PSI 7.6%
Eng. #2 75 PSI 55 PSI 20 PSI 26.7%
If compression is poor, look for
1. Loose cylinder head bolts
2. Blown head gasket
3. Burned valves, valve seats and/or loose valve
seats
4. Insufficient tappet clearance
5. Warped cylinder head
6. Warped valve stems
7. Worn bore and/or rings
8. Broken connecting rods
Cylinder Leakdown Test
The cylinder leakdown tester, Tool # 19413, may be
used to test the sealing capability of the compression
components of each cylinder and quickly identify the
problem component.
Cylinder Balance Test
If the engine is hard starting, runs rough, misses or
lacks power, perform a cylinder balance test to
determine whether both cylinders are operating to their
full potential.

rayjay
01-23-2011, 11:23 PM
Flathead motors don't have high compression ratios so 75 to 100 psi would seem about right.

joshockey
01-24-2011, 12:14 PM
larrybl hit it on the nose thats how i went about checking the compression on the motor. as i said i know that cylinder 1 exhaust valve needs work i think it is worn after not running for yrs and after its first start in yrs it might have stretched it out since theres a tapping on that cylinder.

38racing
01-24-2011, 01:47 PM
my old 85 42... puts out 90 on each cylinder

Grand Sierra
02-14-2011, 03:55 PM
I got 78 psi on a Tecumseh OH160 (cold)and 120 PSI on my Skidoo Mach 1 im thinking any more than 150 or so would run on something other than pump fuel. I'll have to check my Kohler Command some time and see what that has.

sgtsampay
02-14-2011, 06:39 PM
My twin 16Hp gets 52ish in both jugs. I wander if something is wrong with it. thats may explain why its a weak 16. LOL.

joshockey
02-14-2011, 08:34 PM
My twin 16Hp gets 52ish in both jugs. I wander if something is wrong with it. thats may explain why its a weak 16. LOL. check the head gaskets one of my twins had a severley blown gasket one whole side was bad and the gaskets are cheap.

Tater305
02-14-2011, 11:19 PM
if it has a blown head gasket that cylinder wont run if it does WOW...on a side note 16hp briggs are not power house.....anyway im a big briggs fan buy everyone i can(mostly flat heads got 4 now have had about 7 at one time) those motors are good for running all day long and give you no problems they are not up there with most power motors but there a good motor as long as you keep up the RPM's they don't like the lower RPM's like an onan

joshockey
03-08-2011, 05:16 AM
wanted to update that after a valve job on my 16hp i now have 90 in cyl 2 and 60 cyl 1 and the tapping hasent gone away either i however did find grind marks on my cam cyl 2 so something is amiss. i also noticed my good running 18hp has the same markings on the came is this a common problem.

Grand Sierra
03-08-2011, 08:10 AM
I posted anything over 150 PSI may need something other than regular fuel and that is incorrect a GM car I had, had 180 PSI and the lowest was 165 of the 8 cylinders. It runs on low octane pump fuel. One other reading I got was 160 PSI on a high performance chainsaw a new Johnsered 72cc.
I have a Briggs and Stratton OHV 15 w/ ring blow by at 75 PSI and was thinking of retesting with that Engine Restore @ your local Wally World and see how much it would bring it up and would it run w/ out smoking? I think it may be worth a try for 8 bucks.