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School me on the F-Twins Cam Chain

3237 Views 7 Replies 5 Participants Last post by  The8hundreds
After discovering that I have a horrible noise when my F800GS is hot, I've spent about 10 hours (seriously) reading various forum posts about the F-Twins (650/700/800) cam chain. I am no master, but I'd like to take a moment and synthesize all of the good info that has been stated over the years. My hope is that I have accurately captured all of the info, and that eventually we can have a nice, concise guide for those who need it. Warning: All info has been stolen from various individuals, and so I'd like to take this moment to say thanks to JRWooden, JoelWisman, Jocke(TheJoker), Indy Unlimited, itsatdm, Wacholek, and a bunch more - I stand on the shoulders of giants. Err... I plagiarized from the shoulders of giants?

Second warning: I am just a dude behind a keyboard with no formal mechanical training, take nothing below as advice before doing your own research.

My plan is to break up each area into sections. If I've misstated something in this post, please let me (and other readers) know which section you are talking about specifically. I'd like to treat this like an editorial process, and eventually blow this thread away and create a version 2.0 with accurate (and concise) info.

This will be cross-posted several places.


Section 1:
What is a cam chain and what are the F-Twin components:
The chain "synchronizes the rotation of the crankshaft and the camshaft(s) so that the engine's valves open and close at the proper times during each cylinder's intake and exhaust strokes. In an interference engine the timing chain is also critical to preventing the piston from striking the valves."

The F-Twins system is comprised of the chain itself (#11 in the photo), three chain guides to prevent the chain from moving incorrectly (#'s 10, 12, 14), and a tensioner (#15) that takes up slack as the engine heats up and parts wear.


Section 2:
How often do these things wear out and on what bikes?
From all my reading, riders have needed to change their timing chains at many different mileages. I noted people replacing them at 25k, 45k, 35k, 42k, 52k, and 92k miles. However, several rides have noted that they haven't needed to change anything for 100k+ miles.
From all my reading, I saw little to no mention of any chains actually breaking.
It also seems that the F800 (compared to the F650 or F700) is the most susceptible to chain system wear, which is probably due to a higher cam profile, long travel, and the lightweight flywheel design.
A theory of why they wear: "the crankshaft accelerates and decelerates considerably between each combustion stroke. This and the cam shafts aggressive profile results in the timing chain loading and then becoming slack twitch per crank shaft revolution. This repeated slackening and then tension results in the rapid stretching of the timing chain with the currently spece'd units."

Section 3:
What can wear in the system:

Chain: The chain itself can wear over time (sometimes mistakenly called "stretch") as the small pins and plates of the chain loose metal. This will cause the chain to become physically longer.

Chain Guides: The guides are made of plastic and generally last a long time, but they can wear out, especially as the cam chain lengthens. Also, these guides can break. Breakage of these guides have been noted by several individuals, especially if the valve cover was hamfistedly placed back on the engine after a valve check.

Tensioner/Dampener: The tensioner can fail to provide proper tension for the system, generally too little force. The tensioner can reach its limit of travel, which would tend to happen if the chain or guides are very worn. The small check valve in the tensioner could get stuck due to particulates in the oil. Running improper oil could also cause problems (BMW now calls for 15w-50 to be used). Note: we can argue whether the chain is tensioned or dampened, but BMW calls this part a "tensioner."

Section 3A:
How the Tensioner works:
The tensioner is composed of a hydraulic piston with a check valve, a spring, and the retaining cap screw. The tensioner pushes on one of the cam guides (#12 above) to provide the (hopefully) proper tension on the cam chain. If the bike has sat a while, the tensioner will generally loose oil pressure, so the spring provides some tension for the first few seconds of engine startup/run. Unlink some other manufactures, there is no ratchet mechanism to prevent the tensioner from receding when the bike is off. After the first few seconds, the check valve should fill the tensioner with oil. This is accomplished as engine oil pressure builds from one of the oil runs, and as the chain oscillates front and back. As the cam chain wears, the tensioner needs to extend farther and farther to provide the proper tension.


Section 4:
Tensioner update:
In (roughly) 2011 BMW released a new, updated version of the tensioner components, while also combining the whole assembly as one unit when you go to purchase it. It appears that the previous version's part number was: 11 31 7 695 823, while the new tensioner is part number: 11 31 8 531 009 (as of May 2021). Several riders who have compared the old/new parts noted that the internal spring was slightly longer/stouter than the previous version. (The original spring part number may have been: 11117715438, but can not confirm.) While the bolt holding in the tensioner was previously hollow with the ball valve at the back/side, the new one is a solid bolt. The new bolt also comes with a washer, whereas the old bolt had a flange between the head and threads.

Section 5:
How do I know I have a problem?

Without digging into the engine:
Section 5A: Noise
(This statement is kinda fishy) There are three somewhat distinct noises that could indicate a problem. Start up death rattle, improper valves, and hot-bike-cam-noise.
5A1: Start up death rattle: Due to some tolerance in the cam chain tensioner piston, oil will slowly leak out of the tensioner as the bike sits. In the first 4 to 5 seconds of the bike firing, especially after sitting for a while, expect that you will hear some increased noise from the engine. Some describe it as a bunch of marbles flinging around inside the engine case. If the bike only rattles for a few seconds, it's generally accepted that this is a good thing, as it indicates that your tensioner is working properly. During this time, it's not ideal to rev the engine above idle speed until the tensioner has had time to fill. As the oil "ages" and becomes thinner, you may hear a longer rattle at startup.
5A2: Improper valves: If after 5 seconds, but before the bike is hot, you may hear improperly set valves. This would probably carry through an increased RPM range. You could also hear improperly set valves and cam chain noise, but the cam chain would generally get quieter with increased RPMs.
5A3: Noise after he bike is hot (hot-bike-cam-noise): If the valves are set correctly and the bike is still noisy at idle after ~20 minutes at speed, then again, you probably have a problem with the cam chain system (either/all the guides, chain, or tensioner have worn). The bike will probably "not make noise at higher RPMs as the crank does have enough rotating inertia to keep the chain under tension for the brief intervals between combustion cycles at these higher speeds, so, initially you hear [chain noise at low RPM's]… It is the only component that rattles only once the engine is hot hot but initially at no other time. The rattle is completely unmistakeable, anything short of a deaf guy will hear it and know it can't be right."

5B: Power loss:
"As timing chain wears (elongates) the valve timing slowly retards, [resulting in a] gradual loss in power so after a replacement, you may notice and increase in power and smoother running engine"
Note: this will probably happen over a lot of time, so I would say it's not the best indicator

Digging into the engine:
5C: Guide Wear
A lot of wear of the chain guides would indicate a stretched chain or improper tensioner. It was noted that the wear limit for one of the guides is 0.8mm (this is unconfirmed).

5D: Seeing timing incorrect
During a valve clearance check, the cam sprocket timing marks (EX and IX) are to be set facing each other with the bike at TDC. If the chain is stretched, one or both of the marks will be off, sometimes very significantly.

5E: Measuring chain stretch
To date, BMW does not specify any way to measure chain stretch. Some riders and techs note that there is a reference in the RepRom for a special tool that is inserted into the chain tensioner hole to measure stretch. It has been stated that BMW dealers can access this tool, but no one, including some BMW dealers, are able to find it. My 2015 copy of the RepRom does not list the tool, nor the procedure anywhere that I have been able to find.

You could attempt to do a pin-to-pin measurement of a known "good" chain and compare it to your chain, but since you only have access to a relatively short length of chain, it may not be a very good method.

One rider did note that "the old one was about 10mm longer than the new one, and could be bent sideways much more sharply - both clear indications of inter-link wear."

5F: Measuring sag
Several riders have noted that there is an excessive amount of sag in the chain between the two cam sprockets. Upon changing the cam chain, the sag goes away. Again, BMW does not specify any way to measure chain sag. This probably isn't a perfect way of determining the need to change the chain, as the tensioner system should take some of this sag out while the bike is running.
See the two vides by Jocke:


No Sag:

5G: Does my tensioner work?
In order to determine if the tensioner is at least able to hold pressure, you have to remove the tensioner from the engine, place it in an oil bath and pump it. The tensioner should be hard to compress and does not move once loaded with oil. Note: This doesn't tell you if you have exceeded the limit the tensioner is able to provide.

Section 6:

Can I prevent the problem?
May riders are changing out their tensioners at regular intervals. BMW does not have a specification for this, but it appears that most riders are planning on changing the tensioner out at 20,000 miles to 36,000 miles. One person noted changing the tensioner at a 12,000 miles interval, noting an improvement each time.
One rider noted that keeping the bike above 3,000 RPMs will decrease vibrations from the engine. Their theory noted "Those vibrations came form the very lightweight crankshaft construction. [During] that low RPM, [the] crankshaft has very variable speed. It speeds up after the ignition and then slows down. And all that is done in [a] single turn of the crankshaft. That cause a lot of jerking on the timing chain and stretching it over time."
This same rider also noted "I have noticed that high oil level is not good for those engine. I mean like MAX on the meter. It seems that when there is high level of oil the small sump at the bottom of the crankcase (the one which oil is sucked by the second oil pomp) fill up with oil and that oil obstruct the move of the crank. I did that experiment 4 times on different temperature conditions. That would explain why some engines rattle having 16k km on the clock and some without any problems running up to 70k km. Both the same year of manufacture.
In conclusion. I strongly believe that low level of oil (not below MIN) and riding on higher rpm's ( above 3500) will prolong timing chain life."

6D: Manual chain tensioner
Mixed opinions on whether this is good or bad. "I would expect that with the automatic chain tensioner, the chain wears slower than with the manual. With the manual, the chain tension is not expected to be correct all the time." Personally, I think that if Rotax wanted to go this way, they would have? Also "could a manual tensioner block oil flow? [since the tensioner is in the oil path]"


Section 7:
Houston, we may have a problem!
7A: Double check that there isn't air leaking from the gasket on the clutch cover. "There is a torque spec AND sequence for the clutch cover. This is specd for a reason. Either a tech or owner not paying attention to the instructions for bolting on the clutch cover will increase the startup rattle AND reduce oil pressure to the rest of the motor as well as foam the oil." This seems like an easy place to start.
7B: I only seem to have a tensioner problem:
Fix - replace the tensioner. Some individuals have found that during a hot start, they will still get the death rattle. Those same individuals have noted that after changing their tensioner, the hot-start death rattle has gone away.
Notes for changing the tensioner:
Using the top dead center (TDC) timing hole and locking screw, lock the engine at TDC. "When the motor is at TDC, there is very little tension on the back side of the chain where the tensioner puts it's pressure. You can easily thread the tensioner by hand with no force."

"When I took my tensioner out to inspect the spring I noticed the cross-drilled "fill hole" was oriented at about 9:00. The oil inlet and outlet holes to the tensioner bore are located at about 2:00 and 4:00 so when I reinstalled the tensioner I placed the fill-hole at about 3:00. I swear the start-up rattle is now shorter in duration... but have no hard data on it…"


Section 8:
Houston, we are changing the chain!
Generally, it seems that if you're going to go this deep, it's a good idea to get a new chain, set of guides, and a new tensioner. That way everything is working as it should, and no part is already worn.

Note: The official BMW way of changing the chain is to remove the engine from the bike and tear the engine half way down. Several folks (hat tip to them) have found that purchasing the BMW chain, breaking it, and using a master link from Z-1 Enterprises allows you to save about 32 hours of work.

If going the master link route:

8A Part list:
Part numbers for 13-15 F800GS (same as others?xxx) :

11 31 7 689 494 - Sliding Piece
11 31 7 690 475 - Timing Chain
11 31 7 690 493 - Chain Tensioner
11 31 8 531 493 - Guide Rail
11 31 8 531 009 - Set of Chain Tensioners

To access the chain tensioner (11 31 7 690 493) which is held on by a screw, you'll need to open up the clutch cover, so a new clutch cover gasket will be needed:
11 11 7 707 906 - Gasket Left

BMW Special tools:
Locking screw to lock engine at TDC: Part number: 11 6 570 - Locking Screw

Master link from Z-1 Enterprises - Part number: 82 RH 2015


Section 9:
Basic, Basic Process to change the chain:
[This will be documented later]
- Get to the valve cover and remove it
- Remove the clutch cover
- Rotate the motor to #1 TDC and lock the engine
- Remove the cam bearing plate
- Remove the cam chain tensioner
- Remove the intake and exhaust cams, thereby freeing the chain
- Cover everything
- Grind the pins of the old cam chain and slide out the pin
- Attach the new cam chain to the old cam chain
- Remove the TDC locking bolt
- Rotate the rear wheel in 6th gear; gently to pull the new cam chain around the bottom of the engine
- Make sure the motor is at #1 TDC and lock the engine
- Install the intake and exhaust cams, taking care to make sure you have the right timing
- Rivet the new chain's master link
- Install the all the new guides
- Install the new tensioner
- Install the cam bearing plate and clutch cover
- Double check everything
- Pray to the motorcycle gods
- Pray to the gods you offended by praying to the motorcycle gods first
- Button the rest of it back up
- Pray one more time to whomever you'd like
- Start the bike up and smile at your success


Whoa - you read this far - thanks!!! Sooooo... what did I get wrong???
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Can you take a video/sound recording of the noise? Where does it sound loudest? The Camchain is on the left hand side of the bike, so if it is an issue it should be prevalent there.
I think I'll plan on taking a series of videos. One during the death rattle start up, one a minute or two later, then again after a ~10 minute ride. I snapped a photo of the stretched cam chain when I was in the bike last. I'll post that when I have time.
You might want to duplicate your post and any further information regarding this subject in the "Hall of Wisdom". See the link to the right of the New Posts line.
You think this is worthy of the HoW?? [:D]
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