Low compression on rear cylinder

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Nov 24, 2021 | 01:27 PM

alok_pandey

Thread Starter

Stage II

Joined: Nov 2021

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From: Pleasanton

Low compression on rear cylinder

Hi,

I was on I-5 a couple weeks ago riding to LA on my 2018 CVO limited edition. I was cruising at 75 mostly but I did speed up to 100+ for a few seconds in between. After around 250 miles of ride (I did stop twice for gas), around Bakersfield, my engine started to crank and then gradually my bike shutdown, I pulled the clutch and went on to the shoulder. after waiting for 10 mins I was able to start the bike but the engine light turned on. I slowly took it to the next exit and parked in a gas station. I then found a HD service center which was open in Bakersfield, I was able to ride 30 miles to get there, I rode pretty slow though (55-60). The technician looked at the engine light error code and told me that it's low on coolant, he filled the coolant and also checked the engine oil, surprisingly the engine oil was too low, he filled 3 and 1/2 quarts of engine oil. I had done 10K service on the bike and it was at 13.7K so no reason for engine oil to go so low (there is apparently no leak). I then started to ride towards LA and after 25 miles of ride the bike shutdown again, I was sensing some different engine sound all the time from rear. This time I couldn't start the bike even after waiting 30 mins. I had to tow it to HD service. They have investigated the problem and yesterday I got a call that the problem is due to low compression on rear cylinder. They are tearing down the engine to find out the real reason. The tear down cost itself is ~900 dollars, I am now worried what might be the actual cause and how much more I might end up paying. Any expert advise or comments would be really helpful.

Thanks

Nov 24, 2021 | 01:54 PM

702

Seasoned HDF Member

Joined: May 2018

Posts: 5,814

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From: Las Vegas

Do some research on "sumping" in the M8 forum here to see if any of the symptoms you noticed matches this issue.

Here's one thread to get you started.

https://www.hdforums.com/forum/milwaukee-eight-m8/1266192-how-do-i-know-if-when-my-bike-is-sumping.html

Last edited by 702; Nov 24, 2021 at 02:06 PM.

Nov 24, 2021 | 05:44 PM

svarnster

Road Warrior

Joined: Jul 2011

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From: coastal sc

I hope it all works out ok. now is the time for all of those engine mods you have been thinking of, cause that does not sound like a good situation. I would be looking at crank work, big bore, and cams. Making lemonade!

Nov 24, 2021 | 08:31 PM

hattitude

Seasoned HDF Member

Joined: Sep 2008

Posts: 14,160

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From: San Diego, CA

Quote:

Originally Posted by alok_pandey

I had to tow it to HD service. They have investigated the problem and yesterday I got a call that the problem is due to low compression on rear cylinder. They are tearing down the engine to find out the real reason. The tear down cost itself is ~900 dollars, I am now worried what might be the actual cause and how much more I might end up paying. Any expert advise or comments would be really helpful.

Thanks

I'm certainly no expert, but even so, it would be hard to say just what happened from just that description......

Based on the engine light being low coolant.... could be it overheated, compromised the rear head gasket, which led to the loss of oil and eventually the loss of compression.. But that's just one of many possibilities...

Based on the engine not running, and no compression, it needs to be taken apart like the dealer is doing, to know/learn anything for sure.....

As mentioned, if you ever entertained the thoughts of doing engine mods to your bike, now may be the time. Whatever they find, they'll need to disassemble for diagnosis, buy parts, and then reassemble for the repair. You'll be paying for the parts & labor anyways... may as well put it back together with "good performance" parts.... Let the depth of the tear down be an opportunity, and decide what engine mods (Stage 2, 3, 4, or performance rebuild) you'll have them do..... But I have to admit, I have the sickness...!

Hope it's something simple relatively simple like just a valve or a head gasket, but keep us posted and good luck with the repair...

Nov 24, 2021 | 09:35 PM

pgreer

Stellar HDF Member

Joined: Aug 2020

Posts: 3,182

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From: College Station, TX

Yep, sounds like oil sumpping. But you can't tell if or how much damage there is without some disassembly. But low compression on the rear cylinder indicates internal damage.

best of luck
Paul

Nov 26, 2021 | 05:09 PM

handirifle

Seasoned HDF Member

Joined: Sep 2018

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From: Kalifornia

I would imagine the next thing the dealer checked would be the primary oil level, would be obvious if it was sumping. My guess is rear cyl compression rings seized. Maybe due to overheat from lost coolant?

Just a guess.

Nov 26, 2021 | 05:49 PM

702

Seasoned HDF Member

Joined: May 2018

Posts: 5,814

Likes: 7,147

From: Las Vegas

Quote:

Originally Posted by handirifle

I would imagine the next thing the dealer checked would be the primary oil level, would be obvious if it was sumping. My guess is rear cyl compression rings seized. Maybe due to overheat from lost coolant?

Just a guess.

Transfer and sumping are 2 different issues, and one has nothing to do with the other.