Compression tester

[RobThomas]

Brain fade. A quick test of this new (new to me, anyway) Sidevalve engine gives between 92 and 100 psi turning it over on the starter, plugs out, throttle wide open and spinning fast. A quick look at the internet suggests that many people now just divide the pressure by 14.2 to get the approximate comp ratio whereas I had always subtracted 14 from the pressure to start with. It starts to make a difference on low comp engines.
The engine is meant to be about 6.6:1 ratio so I'm low, but how low? Some Blue smoke evident but it is the original engine, albeit rebuilt in 1990 and an unknown mileage since then (possibly nil).
Any thoughts?
Ta.

[alanworland]

Does seem a bit low but as long as their pretty much the same and the engine isn't burning a lot of oil I wouldn't worry too much.
I checked mine only recently and bearing in mind I have skimmed the head my readings were 125/130. Mines done 80k since rebuild.
Don't forget to use anti valve seat recession additives, I use Castrol Valvemaster.

Alan

[RobThomas]

Thanks, Alan.

I placed a thin plastic bag over the oil filler hole and, apart from spatter, there was little activity. I half expected the bag to inflate and fly off into the distance.

Possibly there is contamination of the fuel by virtue of old father time, the car having not moved under steam in many years. I'll need to gather some fuel cans and do a run to the shops to fill it with fresh stuff. I dropped some MMO (Marvel Mystery Oil) into the fuel tank so that might also explain a little of the faint blue haze. I got 92/92/100/96 on the dry figures. I didn't do wet ones since it isn't easy to get the oil to the right area.

Your 130 psi sounds right with a 30% increase in comp ratio towards 8:1. Maybe I'm not too far off, after all. Oh well, it's just a guide figure, after all.

[RobThomas]

As an aside, at idle it sits at 15.5 AFR, goes to 14.5 just above low idle (1000 rpm?) and rises to about 13.5 above circa 3000 rpm. Not bad. EK needle. It has the heavyweight carb damper and a small inner spring to help keep the mixture sensible under acceleration.



Just 'oiled' the bores with a syringe to get the oil round the corner. Almost a perfect 100 on all 4 with the worst going from 92 to 98

[philthehill]

AFR...………………...Air Fuel Ratio.

[alanworland]

Were those AFR figures 'under load'?
I manufactured inlet manifolds to enable the intakes to breath better and they now use a pair of hs1 carbs equipped with (I'm fairly sure) EK needles. To set the mixture I have removed plugs after a good run until a good looking plug colour was achieved. Not very scientific I know!
This has resulted in a rich tickover, but not rich enough to hunt.
I'm sure that from the many needles available this situation could be put right.
I think the book suggests lifting the piston 1/32 which should give a momentary increase in tickover.
Much better to run rich than lean, don't want to burn valves out.

Alan

[pgp001]

I am curious to know how AFR figures are obtained please.

Thanks
Phil

[philthehill]

https://en.wikipedia.org/wiki/Air%E2%80%93fuel_ratio

For every day use and determining air fuel ratio the type of machine in the link below is useful.

https://www.ebay.co.uk/itm/Gunson-Gaste ... SwSP9bVyHy

[RobThomas]

pgp001. I use a wideband kit from Innovate.

https://www.innovatemotorsports.com/press/pr-lm1.php

Lots of stuff on that site. My kit has a dial that reads and displays the AFR straight from the tailpipe of any car via an adapter I made.

Alan. those were static figures under no load. I need to get decent tyres fitted before any good running can be done. 30+ year old crossplies at the moment, from Yugoslavia (Hasn't existed for decades!)

[alanworland]

Looks a useful bit of kit - not cheap though!
Fully understand about the tyres!

Alan

[craigb]

A bit slow off the mark answering Rob. I bought a SV driveline to get a few parts. The guy said it had been rebuilt (how many times have you heard that!) so when it arrived I stuck the compression tester on, just as you described and I got bang on 100 in each. When i pulled the clutch off I notice the flywheel had been refaced and perfectly flat which also might suggest work done. None of that matters but just to add that maybe the 100 is right for a stock engine. Not a sidevalve or morris, but remember having a car with slightly uneven compression with low miles but sitting for a long time. Put some redex down the bores (haven't seen that stuff over here for years) and ran it for a while and rechecked and it all evened up. I suppose valves that sit open could corrode a bit and sticky rings and who knows after a good run. They don't seem too bad anyway.

[RobThomas]

Thanks, Craig. That's reassuring.

With regards to redex, I have one small tin of the original stuff left which is quite different to the stuff they sell no. I think the modern version is more of a fuel system cleaning product. I bought a bottle of Marvel mystery Oil on a trans-Atlantic jaunt to try as a replacement following some articles in an aviation jornal. Piper Cubs suffer from long term wear on conical brass valves in the fuel line but if you put a couple of drops of MMO in the fuel it is said (YMMV) that it reduces the wear. I know that MMO was also added to the fuel in the B29 Superfortress for the notoriious P&W Corcob engine to help keep them running.

http://i.imgur.com/K58NHqt.jpg

[StillGotMy1stCar]

Nice link to an impressive engine.
Could you get the engineer over please I appear to have a slight misfire on cylinder 26…

[RobThomas]

After some tinkering with the wideband via a laptop I am running it in Lambda mode instead of AFR mode, thus eliminating any errors that may creep in from modern fuels. The results are quite satisfying. At idle it sits bang on stoichiometric (1.0), suggesting a perfect richness, although it could be leaned out a little to improve fuel economy. Under acceleration it richens to a momentary figure of just over 0.8 and settles quickly at 0.85, which is just the perfect richness under load to get maximum power from the sidevalve. Looks like the EK needle isideal for the job.
I'm still getting a little smoke out of the filler tube but the exhaust seems a lot cleaner and smalls better.

[geoberni]

I dropped some MMO (Marvel Mystery Oil) into the fuel tank so that might also explain a little of the faint blue haze.

I'd never heard of MMO, so I looked it up and found a 1* review on Amazon
with this comment

A Marvel Mystery Oil sample tested for an NTSB post aircraft accident investigation published in 2003 found it to be composed of 74 percent mineral oil, 25 percent stoddard solvent (white spirit), and 1 percent lard.

I realise that all such reviews must be taken with a pinch of salt, but what's meant to be great about it?

[RobThomas]

A bit like gun barrel lube, which is generally 50% Lard, 50% Beeswax. I does the job of lubricating quite well and often better than modern alternatives. In the case of fuel taps, it adds a lubricant that prevents or reduces metal-metal Brass contact when the tap is turned during every flight so that the taps don't wear down. being tapered, the taps wear inwards until suddenly the tap no longer seals.
I use Lard/Beeswax in my .44 revolver and it is the best lubricant to prevent fouling and clogging. I tried Moly Grease and whilst it did lubricate, it wasn't so easy to clean off.
I guess redex was the same, just adding a lubricant to the engine bits and bobs during start.


https://www.ntsb.gov/_layouts/ntsb.avia ... 1610&key=1


Marvel Mystery Oil logo
Marvel Mystery Oil is a product of the Marvel Oil Company, founded by Burt Pierce in 1923.[1] It is used as a fuel additive, oil additive, corrosion inhibitor, penetrating oil, and transmission leak stopper and seal relubricator.

It is composed primarily of petroleum distillates, including mineral oil (60-100%), mineral spirits {10-30%}, tricresyl phosphate (an antiwear and extreme pressure additive in lubricants, 0.1-1.0%), ortho dichlorobenzene (a softening and removing agent for carbon-based contamination on metal surfaces, 0.1-1.0%), and para dichlorobenzene (a precursor used in the production of chemically and thermally resistant polymers, <0.1%).