Dreaded Cam Chain Guide

Britman

XS650 Addict
Messages
239
Reaction score
722
Points
93
Location
Fredericksburg Va.
I recently bought a 79 XS as a flip project that has a dreaded metallic noise from the right hand top of the motor. The screw up is entirely mine for not inspecting the bike closely during purchase and just being in an overall rush to find something else to wrench on. Adding insult to injury I overpaid for the machine's condition and looking back I am pretty sure the seller knew of the problem, hopefully karma will come into play there. The bike is very rough, but it has compression and is complete and restorable. Having spent a while researching threads on this site, looking at You Tube videos, I am about 90% sure it is the cam chain guide, although there was no debris in the blacken oil when drained. It has been years since I went into the internals of a motor, preferring now just to bring a bike back with cosmetics and starting with a good engine as a base. I have spent a couple of days looking at options that would save my pocketbook as much as possible to remedy the situation. The advice given on this site from those folks with more knowledge than I could ever possess is always sincerely appreciated. I am tired of licking my wounds and want to move on to a course of action. Here is what has been running through my old 74 year brain so far.

(Option 1.)
Say "Hold My Beer", pull the damn motor and dig end. It would not be easy at my age and I have forgotten a lot since doing a few old Triumph and Honda twins many many years ago. I also know we now have the web, folks have been there before me, done the job, recorded the procedure, and there are many great threads on this site with documentation on cam chain guide replacement. I also fully understand I really won't know what is involved cost wise until I look inside, but I really really would like to rectify problem with the least amount of money possible to get the bike up and running for resale. There are several questions I still have even after all the research?
A. Has anyone ever pulled the head only, leaving the jugs in place to replace the guide from the top, and not had the cylinder base leak on reassembly? Any odds on the success rate?
B. Since the bike has good compression what are the chances if I do pull the cylinders that I can put it back up with with the original pistons and rings or just ring replacement with a mild hone at a minimum trying to stay away from a machine shop. I have looked at the cylinder walls with my inspection camera and they look good. I know there are a lot of what if's and unknown variables in these questions but any input would greatly appreciated. I would have to say this option has top billing currently. Even if it is worst than I anticipate when I get inside I cannot always convert to to option 2.......

(Option 2.)
Just sell the damn thing as good parts bike with a title. This would be biting the bullet and accepting the substantial loss a true life lesson reminding an "Old Fart" not to be in such a hurry the next time and it would not cost me anymore money....

(Option 3.)
Try to find a good replacement motor. This is not top on my list, since I very well could end up with something worst than what I already have.

Whatever path I go down, I will try and make the most of it and enjoy the process. There is an old saying "Every problem is an opportunity", my future is golden currently.
 
Before you make a decision make sure you do some checking on the bike. Cam chain adjustment and valve clearance ect. Also make sure you don't have any exhaust leaks where the header meets the head. A couple of years ago I had a metallic noise in the top of my engine. Long story short the noise was a small exhaust leak at the head joint.
 
You might be surprised what you find just doing a quick, cursory look at normal tune up stuff.

I was out doing a cam chain and valve adjustment on my newly acquired 1980 Special today that is in beautiful, mint condition and only 7,000 easy miles.

When I test rode it prior to purchase it sounded like the top end was coming apart....but as good a shape as the bike was in I figured it just needed some easy maintenance.

I was right...cam chain was way, way loose.

The intake valves for some stupid reason, were set at .70mm!! They're supposed to be set at .06mm. You could have drove a Mack truck through that clearance...no damn wonder it was clanging and banging when I test rode it before! 😳
 
Yeah, I had a loud metallic noise suddenly in my '76 XS650C - the troublesome Lucille :yikes: - and it did turn out to be the front timing (i.e. cam) chain guide - which disintegrated.

A few things I learned through that incident:
  • you cannot change the guide with the engine in the frame;
  • pulling the engine is not a bad job if you have a helper - and is quite doable alone;
  • disassembling engine after removing it from the frame will take about 30 minutes;
  • changing the timing chain guide is not difficult, but you must remove the cylinder head (the camshaft/rocker cover is not sufficient);
  • the timing chain guides on these older bikes can delaminate - and the deterioration process will be visible when large "slivers" of hard black plastic appear in the oil sump (the flat plate held on by six 6mm bolts on the underside of the engine);
  • if the plastic guide element completely falls off the metallic shoe (as mine did), the bike will be noisy, but it will continue to run pretty well and it should get you home.
I rode Lucille home more than 80 km (about 50 miles) after the guide fell apart and didn't really notice any difference, except the clanking noise in the top end.

Here is a linky to my travails with the front cam chain guide - the good stuff starts at post 52. Before that the thread is just some diagnosis and an embarrassing incident with a compression tester (WTF was I thinking?). Anyhow, I did a whole bunch of measurements and now own one of the largest collections of front timing chain guides on the forum (except for @gggGary, of course).

Anyhow, lots of fun indeed!

Pete
 
Last edited:
Thanks one and all for the replies. I failed to mention that I had indeed adjusted the cam chain and valves to spec. They were not excessively out and I pulled the cam chain adjustor rod out and the copper washer was in place. I will indeed check further before completely pulling the motor, but I am not expecting good news. I checked my old tool box drawer and I still have a couple of hones, both ball and spring loaded, probably the wrong size for the bore, but I do hope a couple of the old memory synapses refire if needed. I appreciate the name of the guide supplier, some rather negative comments were mentioned concerning another well known source. I must admit I would not even think of doing this if this site wasn't here for support. I will post if I make the decision to go in.....BTW the bike is showing around 18 k on the clock, but it looks like someone has been in before, messy sealant around the cylinder head base and with the camera you can still barely see some cross hatching on the walls plus the valves look almost new. I guess it could very well be a botched rebuild but the mystery certainly cannot be solved by standing next to lift wishing for the hindsight Gods to appear. Of course I was told "It was running when parked" like every project on Craigs List. I had a tee shirt made with that on the front I wear occasionally, always draws a comment or two.
 
Thanks one and all for the replies. I failed to mention that I had indeed adjusted the cam chain and valves to spec. They were not excessively out and I pulled the cam chain adjustor rod out and the copper washer was in place. I will indeed check further before completely pulling the motor, but I am not expecting good news. I checked my old tool box drawer and I still have a couple of hones, both ball and spring loaded, probably the wrong size for the bore, but I do hope a couple of the old memory synapses refire if needed. I appreciate the name of the guide supplier, some rather negative comments were mentioned concerning another well known source. I must admit I would not even think of doing this if this site wasn't here for support. I will post if I make the decision to go in.....BTW the bike is showing around 18 k on the clock, but it looks like someone has been in before, messy sealant around the cylinder head base and with the camera you can still barely see some cross hatching on the walls plus the valves look almost new. I guess it could very well be a botched rebuild but the mystery certainly cannot be solved by standing next to lift wishing for the hindsight Gods to appear. Of course I was told "It was running when parked" like every project on Craigs List. I had a tee shirt made with that on the front I wear occasionally, always draws a comment or two.

Buying these old bikes is akin to an old archeological dig sometimes.

We get to dig through, layer by layer to find what the previous owner or owners have bodged in their previous spanner travels...never know what were gonna find! 😳
 
Tagging/bagging, making piles, and having a big bowl of Wheaties every morning.....
 

Attachments

  • IMG_1145.JPG
    IMG_1145.JPG
    487.7 KB · Views: 103
Not great news but I will have to say the motor was not bad to get out. No problems with that at all, "however" the inside was not so kind to me. Top part of the guide rubber was gone completely and quite a bit of rubber at the bottom of jugs. I think a piece of the metal guide itself must have got into the right side cylinder causing some scaring that you can feel with your fingertip and see on the piston. It is already over 25 so I think I may be looking at another set of jugs and pistons from a real low mileage bike that have been reconditioned and ready to go with rings only as one possible option. It is a shame the left side still has the cross hatching visible, why in the hell would you do a rebuild and not install a new guide. I will fix it one way or the other, it has now become a quest. I must admit I did enjoy the process of breaking one open again, even though the news was not good. Going to drown my sorrows with a big plate of chickens tenders with some soft serve ice cream for dessert.....
 

Attachments

  • IMG_1161.JPG
    IMG_1161.JPG
    374.7 KB · Views: 142
  • IMG_1166.JPG
    IMG_1166.JPG
    408.6 KB · Views: 139
  • IMG_1167.JPG
    IMG_1167.JPG
    379.5 KB · Views: 141
  • IMG_1164.JPG
    IMG_1164.JPG
    479.8 KB · Views: 143
Notice some lines in the other cylinder also 5 o clock and 8 o Clock

The pistons I have seen have had a done on the top. These not stock ??
I once had a piston looking akin to that .In my case it was to little oil in the engine I do believe --- I F***ed up

Putting it out here in this case after a rebuild getting the clearance om the tight side not being careful running in taking care on the running in instructions .Overheating and Kabooom
 
What makes you think it's 25 over already? You can't tell really until you clean off the tops of the pistons and read the numbers on them. It looks like that engine may have been starved for oil and suffered a partial seizure sometime in it's past.
 
It is a shame the left side still has the cross hatching visible, why in the hell would you do a rebuild and not install a new guide. I will fix it one way or the other, it has now become a quest.
Yep, the right side has had a pretty significant seizure and the left some too - with cross-hatching still evident. Lack of lubrication, excess heat and the possibility of faulty rebuild (clearances). One solution is re-sleeving - rather than boring to 3rd or 4th oversize - it can be done at home and it's possible to get correct clearances (without boring) if lucky.

The damage (bad lube, excess heat?) also prompts close scrutiny of the rods, rocker shafts and valve guides, etc.
 
It appears by looking at the pic of the bike that it has good bones.

Maybe at this point you'd be money ahead scrounging up another decent used 650 motor somewhere...they're out there and usually pretty inexpensive.
 
I scraped the top of one of the pistons, yes it is 25 over. I am looking at a couple of options, but currently I am walking away for a few days. In prospective I have had numerous bikes go through my garage over the years, some I kept, some I kept for awhile, but most I brought back to halfway decent condition and moved them on and I think I even make a little money on a couple. Most of the time I am happy to at least break even, I just really enjoy the process. This is only the second bike I have considered myself getting burned on, there was a CB450 Honda a long while ago that when I stripped the paint, turd came up, almost gave it away and was overjoyed to see it go.......
 
Back
Top