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Engine overheating and vibrating/knocking a bit too much

3K views 10 replies 4 participants last post by  WayneC 
#1 ·
Hello guys! Long time no see! I have ridden my F650GS (model 2001) from Cape Town (South Africa) to Lusaka (Zambia), and then after some TLC, from Lusaka to Nairobi (Kenya), where I reside.

I've changed the voltage regulator because the old one was dead. Also changed the battery (for a Yuasa one, same as the previous one, from YB12AL-A to YB12AL-A2, I thinl), because initially I thought the battery was dead, before I found out it was the faulty VR. Now with the new VR, all good, it says mildly warm but not hot to burning hot as was the previous one, and it spits a steady 13.5V, around that (I measured some time ago just after I replaced it). So all good from the viewpoint of the power supply, but the engine is knocking/vibrating a bit too much, and the engine is overheating a bit. The fan does go on when required, but it's required too often ;)

I want to say that it didn't appear at once, from one day to the next: this excessive vibrating/knocking settled gradually, from the times I have been running on low battery, it seams. You know, it's pretty much the same symptoms: when your electrical system is not strong enough, the engine doesn't fire quite as neatly as it should, hence the overheating/knocking. At least that's what I have observed... But now that my electrical circuit is 100%, I want to revert to a healthy engine and easy, smooth rides.

I've recently changed the oil and just checked the valve clearances yesterday evening. Of course, on a COLD engine. They are as follows (in mm):
- intake R: 0.10 is ok/easy, 0.15 drags noticeably
- intake L: 0.10 drags slightly, 0.15 drags severely
- exhaust R: 0.25 easy, 0.30 drags, 0.35 no-go
- exhaust L: 0.25 easy, 0.30 still quite easy, 0.35 doesn't go

The Haynes says 0.10 to 0.15 for the intake valves and 0.25 to 0.30 for the exhaust, so we're pretty good here. No signs of excessive wear on the camshaft, looks pretty pristine actually.

Then the spark plug: an original NGK D8EA, hasn't been renewed in a while, was not having any oily deposit, no white deposit either, just the regular dry black stuff. But the electrode gap was quite big: 0.80 gauge went easily, 0.90 didn't go, but almost. The Haynes says 0.6 to 0.7 mm for a healthy electrode gap, so I'm definitely replacing the spark plug, but I was wondering whether there could be something else worth checking, now that I have removed the stuff above the cylinder head... Any idea?

Thanks!
 
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#2 ·
It sounds as though the top end of the engine is in reasonable condition but I would check the valve timing if you've still got the valve cover off. To do this you need to put the engine at TDC which is usually achieved using a crank locking tool. When at TDC, check the timing lines on the two camshaft sprockets to make sure they are horizontal and are inline with the top of the cylinder head. With timing chain wear, you will find the timing lines retard; that is, rotate CW. While you are at it, I would check the timing chain tensioner is still ok (and not in pieces).

You say that you are getting excessive knocking from the engine - does this occur mainly at lower revs (pre-ignition) or over a wide rev range? Normally, assuming you don't have an engine mechanical issue, the knocking sound is either due to the ignition timing (unlikely on the F650GS) or due to carburation; that is too rich a mixture. If this is the cause of your problem then it may be due to a problem with the injector or the O2 sensor which would probably need a BMW dealer to investigate - the alternative would be to substitute these two components with known good ones to see whether that cured the problem. The other reason for getting this type of problem is if the combustion chamber has become 'coked' up due to poor combustion over an extended period. This could then result in overheating and pre-ignition or knocking which would probably require the engine to be 'de-coked'!
 
#3 ·
Hi, thanks for the advice! The engine is still on the bike, haven't even drained its (new) oil, I'm a bit reluctant to do anything major now... But let's go!

For now I have taken pics (attached) of the lines on the camshaft gears that should be aligned... This is the position in which I have checked the valve clearances, so we're at TDC I guess. One can see the lines are not 100% aligned and parallel to the top of the cylinder head... But once I attempt to correct this by rotating one shaft by one tooth on the cam chain, will it then be too much? Must these lines be perfectly aligned, or is there some room for imperfections?
 

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#4 ·
You need to do the check with the crankshaft exactly at TDC - it just needs the right size bolt (M8 x 1.25) with a slightly pointed end to be screwed into the threaded hole provided and then the crankshaft rotated until the bolt engages with the slot in it. The valve timing is probably ok but it is worth doing the check properly just in case it isn't.
 
#6 ·
I'm afraid I'm totally sceptical about the inlet valve clearances being 0.03-0.11mm:think: My BMW service manual gives the clearance as 0.10 - 0.15 mm and my low mileage engine clearances were in the middle of this range which suggests that that is the way Rotax put the engine together. I believe the only downside to have slightly larger clearances is a potentially very small loss in power but the downside to having too small a clearance is a burnt out valve. If you set the valve clearance at 0.03 mm then there's a very good chance that after a relatively small mileage, the clearance will totally close up and you risk damaging the engine!
 
#10 ·
If you check the 2005 TSD, the Dual Spark F650GS & G650GS REPROM plus the Dealer RSD DVD you will find the figures are the same for all year models
Just want to clarify I have a 2001 GS (I think it was out of manufacturing at the end of civil year 2000), single cylinder, single spark, Rotax 650 engine. While WayneC mentions Dual Spark... I don't know if it makes any difference, but just saying...
 
#8 ·
I have come to expect from this group, some excellent advice to members to solve their problems; may I throw in my comments. Rough running accompanied by overheating suggests the mixture is detonating. And several good reasons are offered for this condition. I would replace the old plug with a new spark plug with the correct gap and ask what is the RON rating fuel is used and quality control like in Kenya. Is it possible some one has put a few liters of Diesel, realized the error then topped if off regular 90 octane petrol?

Good luck Alf
 
#9 ·
Thank you Alf, thank you all. Long time since I left the bike standing in my garage, and now I'm in France for medical reasons, so I am thinking of taking advantage of that and buying here a set of those shims needed for the valve clearance adjustment that I will perform once back in Nairobi.

Alf, no: no-one ever put diesel in there, but could be that the octane content is not 100% right here. I will try with expected-to-be-better fuel and keep in mind the possible issue with detonating mixture, but clearly for now, as I haven't put the head cover back on, I'll perform careful clearance adjustment with engine properly locked at TDC, etc.

On our GS, are the adjustment shims small cylindrical coins to slide under the buckets that are directly under the rocker arms, or are the buckets themselves of different thickness at their core? In short, does one add the right-sized shim or change the whole bucket? And what is the diameter, then? Sorry, I don't have the manual here with me... Thanks!
 
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