|
Post by wayne on Mar 7, 2012 18:12:27 GMT -5
I had someone ask me the other day about what is a reasonable compression as they were looking at buying an Re5.
I've had the good fortune to both ride, work on and test more than a dozen rotarys and 7 in less than 12 months. Of those bikes, I've ridden one with compression over 140, another in the high 130's, others in the mid to low 130's, high 120's, mid teens and between 100 and 110. Jess has also voiced his opinion about compression and I've incorporated his thoughts into the list.
I came up with this as a broad guideline if you're looking at purchasing or are testing your own. I've seen three compressions over 140 but only ridden one. That bike was outstanding and backed it up on the dyno by achieving nearly 50 hp. Ten percent more power than the next-best and about 5% more than a demo bike dyno'd back in the day.
Brand new engines should give you something around or over 130 but these do improve once run in.
NB: in the wankel engine, having all three lobes giving similar compression can be more important than the peak reading of any one lobe.
My seat-of-the-pants feeling: With a proper rotary compression gauge and only in my opinion for a used bike:
Outstanding > 140 psi (and rare)
Very good > 130 psi
Good >120 psi
Acceptable > 110 psi
Borderline > 100 psi
Forget it < 100 psi
In practice, it's pretty hard to pick the difference between the 120 and 130 category, they're all good performers. Bikes in the 110 to 120 bracket are still good riders and it would take some experience riding RE5's to really notice the practical difference. Below 110, the loss of power is noticeable but I've got one which will still indicate at least 160 kph (on the standard, optimistic speedo)
By comparison, heres some actual compression readings from the life of a regularly ridden RE5:
First service at 1200 klms - 138
At service 42,000 klms - 134.5
At service 64,000 klms - 116
Edit: Also see Dyno Day thread in Tuning and Troubleshooting if you're researching compression.
|
|
FC Zach
3rd Gear
Eagleville, TN
Posts: 335
|
Post by FC Zach on Mar 9, 2012 3:41:10 GMT -5
The highest reading I've received was 140 PSI
"Forget it < 100 psi" Agree! Although it'll run and ride, it's not going to be at its full potential and typically will barely get out of its own way when the throttle is opened.
|
|
|
Post by wayne on Mar 9, 2012 5:21:13 GMT -5
Glad you posted Zac, I wanted to add to my original post that I'm throwing this up as a discussion item and would like feedback, agree or disagree and what your own experiences are.
Thanks Wayne
|
|
|
Post by Jess on Mar 9, 2012 23:30:53 GMT -5
This is why I stress that you MUST run a compression test on any engine in an unknown bike. I never am ceased to be amazed at what people pay for "ran when parked" I get folks all the time that say..."It has great compression"" I kicked it through..." The only way to tell is to put a meter on it... period. They will start, idle and run just fine at 70 psi. However, The bike won't get out of it's own way. You also probably won't be able to use anything past 3rd gear... I agree with Zach... 90 to 100 psi will run ok, it just won't have any "snap"... Top speed, will be limited to about 80mph in 4th gear. 5th will be useless. Just my 2 cents... Best
|
|
|
Post by wayne on Mar 10, 2012 0:30:25 GMT -5
So Jess, for the rest of us, as far as my mooted guidelines go, are they a reasonable ball park with which to judge ?
|
|
t140v
3rd Gear
Posts: 422
|
Post by t140v on Mar 10, 2012 18:48:46 GMT -5
This is an excellent guide, unfortunately up untill now it has not been available to the general public, RE5's do not come with a tag saying my engine can only make 60psi and is F**d & for spares only, I asked who had a compression tester in October last year and did not get a reply so how do we test. I have a 1977 CB750F2 that should do 120mph @10500rpm but do I really want to make it do that. I am happy to ride 60 - 70 which is the chosen speed of the local vintage bike club, if I want to go faster I can allways jump on the Harley. Out on mine again tomorrow nearly 200miles this week and the season has just started Regards Stuart.
Buy one, get it running and ride it!
|
|
|
Post by wayne on Mar 10, 2012 20:10:34 GMT -5
Jess has told me that you can use a regular compression gauge to get an idea. It's not going to give you lobe by lobe but...........
I have seen regular compression gauges that just have a conical rubber end which you simply forcibly hold in by hand. That way you can circumvent the odd hole size. I was thinking about buying one and doing a compression test and then comparing it to the actual compression gauge to see how close it is.
|
|
|
Post by Jess on Mar 11, 2012 19:08:36 GMT -5
Wayne,
With regard to your figures, I agree.
120 or above is excellent...
100 to 120... should be an enjoyable bike that still has a bunch of life...
Any bike that is sold as "ran when parked" is a recipe for a large hole in the ground that you pour $ into...
Just my 2 cents...
I would not use a "press style gauge" You need to have one that can screw into the 18mm plug hole and has an oring for good sealing. I use one regularly in my shop for a quick test before I get the Suzuki tester out to separate each lobe. I have found that they are very close...
Best,
|
|
FC Zach
3rd Gear
Eagleville, TN
Posts: 335
|
Post by FC Zach on Mar 11, 2012 23:21:18 GMT -5
I asked who had a compression tester in October last year and did not get a reply so how do we test. Just like what has been stated already, you can use a conventional automotive compression tester. These kits should come with adapters for the different diameter and thread sizes, so if you don't already have one, and go to buy one, make sure it has these. Another option and probably the best/most accurate is a kit like this (You can buy the single rotor kit, Model: ReCT-03b): This is similar to what Mazda dealerships use to test rotaries but this kit is a fraction of the price of Mazda's testing equipment. I will be buying one of these sometime soon, I had the privilege to use one on my car and the data logging was outstanding, you can just save graphs to your computer for records. www.rotarydiagnostics.com/model_rect-03b.htm Edit: you would need to put your own adapter on a kit like this since this was made specifically for threading into Mazda spark plug holes.
|
|
|
Post by HGH 770N on Mar 12, 2012 11:24:18 GMT -5
I bought one last year , had a brass thead addaptor made 18 to 14 mm as the flexi pipe it comes with is too long and looses the pressure before the sensor . very easy and portable ,( no paper rolls or ink as with the original Suzuki one,) just your lap top and store the info and print if you wish later, The down side was inport tax and shipping/ insurance to the uk. Rog
|
|
|
Post by HGH 770N on Mar 22, 2012 11:34:27 GMT -5
Reading taken from my bike.Engine number 10320 Owners are welcome to pop in and use it if they are on the M6 between junction 12 & 13 , just MSG me 1st. By R&R's comments my unit thats showing 116 psi should be good for many more miles. Best Rog Attachments:
|
|
|
Post by wayne on Mar 24, 2012 23:04:29 GMT -5
Further to the general guidelines here's another point. If you are buying a bike, it's possible that you'll only get to do a cold test.
Edit: Initially I found big differences between hot and cold testing. However, I've experimented some more with cold testing. Leave the bike turning over as long as possible while observing the gauge. It can take quite a few revolutions before the gauge shows a final peak. Once the gauge stops increasing after numerous revolutions, then you can take that as a good indication regardless of engine temperature.
Also I found that an engine that has sat and probably not started for at least 25 years did increase in compression across all lobes after 1200 klm:
Highest lobe increased by 2 psi, lowest lobe increased by 3.2 psi. The high lobe showed the 2 psi increase within 250 klm and then didn't change. The lowest lobes showed increase at each of 3 tests after the initial delivery test. Who knows, might get even better with more mileage.
|
|
|
Post by HGH 770N on Apr 13, 2012 16:57:02 GMT -5
The Re-test of my Engine number 10320 showing 116psi before now shows 127 psi at the highest peak , this was tacken after a 20 mile ride. .Engine number 10373 , Has been in store not run for years, After engine flush of Oil and Coolant , Check points and timming. Check port valve operating smoothly, Added a squirt of 50-1 mix into plug hole and used kick start to turn over a few times to lube the seals/tips, i used the 50-1 mix in the carb and then used starter motor to crank over engine until oil pressure was up and the pressure light went out. after trying to start and changing spark plug 3 times and using a pre-heated spark plug she fired up burning all the years worth of rubish out of pipes was very smelly like a bonfire , The bike now starts easily runs smoothly but on compression test only showing 99psi high and 70psi low I was not expecting this reading from the way it runs smoothly with no smoke and a clean spark plug. May be the psi will even out and/or improve after some use. i have no way of riding it as yet so can't comment further. Best Rog Engine 10320 Attachments:
|
|
|
Post by HGH 770N on Apr 13, 2012 17:31:45 GMT -5
engine 10373 99 psi high 70 psi low Attachments:
|
|
|
Post by HGH 770N on Apr 13, 2012 18:56:00 GMT -5
Photo of ReCT-03b Comprossion tester with Brass addaptor can be screwed in without removing air box. The Programs are far too many for the RE5 but once used a few times it becomes easy to save settings. Rog Attachments:
|
|