compression test

[kevspeed]

Hi all.......Does anybody know the min/max compression for an RT195 as im having an issue with the engine not revving and im going down every route i can to try and solve the problem. This particular engine measures 130 psi.
Its my fourth RT195 build,so im familiar with the kit and have not had any real issues with previous builds.
Crank 58/107
BGM stator, all coil readings within min/max perameters.
Timing set by strobe at 17 btdc.
Scootronics CDI with diagnostic light, (I have tried another CDI but the problem persists)
22mm Scootopia/Dellorto jetted as per Indian GP200 (i have tried two other 22mm carbs, one Genuine Dellorto but the problem persists).I used this set up on my mrs scoot which runs beautifully.
Big bore box pipe.
The engine starts first kick and ticks over really nicely but will not rev,it just roars as if its struggling for fuel but the tap is delivering ample.
Initially i thought that something electronically may be breaking down under load but testing with the multimeter and replacement of parts hasnt shown any problems.

[ULC Soulagent]

Air leak test?
Squish test ?
Piston round the wrong way?

[kevspeed]

All as per instructions, no air leaks! This is the fourth one ive done,all the others virtually the same spec but without this problem.

[daniel whiteley]

I’ve had similar when big end bearings started to fail

[duncan1958]

Is it possible that the pick up coil is not at the right height?

[Fast n Furious]

Is it possible that the pick up coil is not at the right height?

Incorrect pickup alignment is typical of the issue reported. A worn mag bearing will also give the same result. I suggest that this should be the first thing to check.

Compression pressure measurement on a Lammy is always going to be ambiguous. This is because the rather innaccesible spark plug hole doesn't allow you to screw a gauge directly into the plug hole. Consequently, you ineveitably have to use some form of flexible hose connection between the head and your measuring gauge. By adding in this flexible hose and a bourdon tube gauge, it in effect increases the compressed cylinder volume by a few CC's. So the the reading you get will always be less than true. The kit that you use will no doubt differ slightly from someone elses kit giving different readings on the same engine! So, your reading of 130psi, although it looks good can only be considered as arbitrary.

I use a piezo electric pressure sensor that screws directly into the plug hole. The 0-10V output signal from this sensor is relative to 0-150psi. A digital multimeter with peak maximum voltage detect is then used to determine the peak output voltage.
EG. A peak voltage reading of say 8.5v = 15 x 8.5 = 127.5PSI.
Granted.... This kind of kit is expensive and beyond the average persons toolbox but this is what it takes to be accurate.
This measurement is the corrected measurement. Theoretically, the pressure rises upon closure of the exhaust port. So, your exhaust port timing will have an affect on the measurement you get, as well as the compressed volume of your cylinder head.
In practice, compression begins prior to the closure of the exhaust port which expains why the mathematic calculations for corrected compression differ somewhat from the
practical measurements.
With those £15 compression testing kits with their various adaptors, extension hoses and connectors that you can get from fleabay, a reading of 75 - 90PSI is typical on most 2T Lammy engines. This reading isn't true but can be used to determine if you have a reduction in compression, providing you know what the reading was originally when the engine was new and good.

[kevspeed]

Hi all.......And so it goes on.......
This is what i used for the compression test, a bit antiquated but it stood me well back when i was maintaining my old Fords!
IMG_20230702_153058_HDR by Kevin Payne, on Flickr.
Anyway, the only thing i hadnt tried was a different flywheel as i didnt think i had one......... but when i was rooting around for something else i came accross an old battered AF flywheel (no fins), so i thought i would just try it out....... and it seems a hell of a lot better.....
I had already discounted bearing wear as its a new build and everything in the engine is new apart from the gearbox, flywheel and stator plate.
The odd thing is that the flywheel and stator came off a running engine so i assume that there must be a difference in the depth of the mag housing compared to the engine that the kit came off.
My next tryout was going to be using an old GP Ducati points type flywheel and fix an external pickup kit as everything is adjustable from the outside so it makes life a lot easier!

[ULC Soulagent]

Hi all.......And so it goes on.......
This is what i used for the compression test, a bit antiquated but it stood me well back when i was maintaining my old Fords!
IMG_20230702_153058_HDR by Kevin Payne, on Flickr.
Anyway, the only thing i hadnt tried was a different flywheel as i didnt think i had one......... but when i was rooting around for something else i came accross an old battered AF flywheel (no fins), so i thought i would just try it out....... and it seems a hell of a lot better.....
I had already discounted bearing wear as its a new build and everything in the engine is new apart from the gearbox, flywheel and stator plate.
The odd thing is that the flywheel and stator came off a running engine so i assume that there must be a difference in the depth of the mag housing compared to the engine that the kit came off.
My next tryout was going to be using an old GP Ducati points type flywheel and fix an external pickup kit as everything is adjustable from the outside so it makes life a lot easier!

Good luck

[Fast n Furious]

Agh.
That old gauge is a pucker one though. It has a check valve in the fitting that screws into the plug hole. So the issue I highlighed above doesn't apply.
It's these cheap fleabay kits you have to avoid because these usually have the check valve as part of the gauge or somewhere inbetween and these give you a false reading.

[Dazts1]

I had similar issues with a blocked exhaust. Took me ages to sort it as i tried everything else but that I was convinced it was electronic issues.