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Well, spring is here. Time to put the model railroad away and start messing with the motorcycles again.

I'm wondering how many here have done a compression check on their Rocket? If you've done one or had one done could you post your results? I did a search and only got a couple of hits. Wondering what "normal" is supposed to be and how much variance can there be between cylinders? I just did one and had two testers to use. The results varied by quite a bit except for the difference between cylinders.

For cylinders 1, 2 and 3 respectively I got 140, 170 and 172 on one tester and 165, 190 and 193 on the other tester. Appears there is a problem with cylinder #1 at about 30 psi low but is it low enough to rip apart the engine to investigate? Maybe I've just got really good compression in 2 and 3? I'm experiencing excessive crank case pressure though which was the reason for the check.

Any thoughts appreciated. Thanks.
 

ruzzle

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Oughta be around 210 psi each cylinder, standard engine, with very little variation, if you're doin' it right.................
 

HansO

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I am no expert but I would be investigating that 30 psi difference from the #1 to the others 2 or 3 psi is acceptable but 30psi that can not be good
 

Torque addict

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Oughta be around 210 psi each cylinder, standard engine, with very little variation, if you're doin' it right.................
That's the figure Scott(warp9.9) gave in a previous post somewhere as well whose knowledge I greatly respect but someone else posted that the dealer said around 150 psi. That's why I'm looking for other's real numbers.

Don't know how I'd be screwing it up, it's just the differences in readings between each tester I have making me question both of them. I checked each cylinder 3 times with both testers (re-inserting each time, not consecutively), throttle wide open making sure the O-ring on the fitting was as tight as I could get it.
 

Torque addict

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I am no expert but I would be investigating that 30 psi difference from the #1 to the others 2 or 3 psi is acceptable but 30psi that can not be good
I tend to agree with you but I'd just rather ride than wrench but if I must I must.
 

cusso ken

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I would think that a relatively low compression engine 8.5 to1 would have around 140to 160 lb compression on most V8 petrol engines I have worked on a 9.5 to 1 compression ratio shows 160 to 180 Lb
I don't think the Rocket engine would be any different, a guide would be a maximum of 20lb variation from highest to lowest.I may be wrong but I cannot see a stock R3 engine being much higher than 160Lb
diesels are a different matter ,our Mack Thermodyne B61 engine would test out at an average of 575 psi hot at 1000 rpm with an allowable variation of 50psi ,imagine that compression in a Rocket engine
 

warp9.9

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Time to do a leak down test Brent. I sent a reply with pictures of the head gasket changes Triumph made. Pictures taken by Arto aka R3RTurbo.
Head Gasket Alpha.jpg
Head gasket Brovo.jpg
Head Gasket Charlie.jpg
Head Gasket Delta.jpg
Head Gasket Echo.jpg
Head Gasket Foxtrot.jpg
 

forklift

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If you don't have access to a leak down tester you could put a tea spoon of motor oil in that low cylinder and repeat compression test. If pressure increases it's your piston rings if not then probably a valve issue.
 

Trirocket3

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I would think that a relatively low compression engine 8.5 to1 would have around 140to 160 lb compression on most V8 petrol engines I have worked on a 9.5 to 1 compression ratio shows 160 to 180 Lb

Cam timing will change actual compression.
Redo test dry then wet to determine losses to bore or valves
No 1 cylinder is suspect
 

Torque addict

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Thanks for the responses guys. I will retest with the teaspoon of oil and also do a leak down test.

I guess I need to ask the question is there anyway other way the crankcase can be pressurized other than bad piston rings or a bad piston? If it's my valves or head gasket I don't understand how that pressurizes the crankcase.

For those that don't know or don't remember I should mention that I am running a turbocharger and I only have the excess pressure when I'm in boost. It's so bad I've blown the dipstick/oil fill cap off twice now during sustained high speed runs. The catch can I added to the crankcase vent is constantly filling up with oil mixed with gas. If I stay out of boost the entire ride it's empty.
 

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