In rebuilding my ’75 400F engine, I have some questions about how to determine wear on certain items, and when wear is bad enough that part is required. I have searched for some info here, but am not finding what is needed so I hope some of you can chime in on my questions. Also, I am well aware of the WYIT (While You’re In There) rabbit hole, but I’m trying to keep costs down and prefer not to spend money on parts that could or should last another 30k+ miles. The odometer on this bike shows 26k miles on the engine, and this bike will not be ridden all that hard or be entered into a concours event, I’m just looking for a decent riding machine. So, I have some questions about the cam chain and the tensioning mechanism that I hope some of you can shed some light on. In the end, it’s just a matter of saving at least a couple hundred dollars on new parts if they are not really needed.
For cam chain wear, many measure cam chain length to assess stretching, so I measured inter-pin distance for 8 links when pushed together and then stretched. I did this while the chain was wedged between two pieces of wood to hold the links steady while I measured. For some accuracy, this was done on two sections of the cam chain. The 8 link measurements when pushed in were 4.675 and 4.667 in (about 119.655 mm), and when stretched out 4.707 and 4.709 in (119.575 mm). From this we can calculate a total chain stretching of 0.2 in (4.83 mm). This doesn't seem like much to me, but I'm no expert. That said, I also haven't found anywhere where there is information on such spec limits. What do you think? What is an acceptable level of stretch, and when would the chain definitely need replacing?
Another measure is sideways flexing of the cam chain. Online one can find pics and videos comparing flex on a worn chain side-by-side with a new one. I haven’t seen specs for this type of measurement, so when is sideways movement too much? I measured the side deflection on my chain at 52.5 mm. Does this have to be replaced? Anyone have numbers on flex with a new cam chain?
On the tension guides, I measured the widths on both the chain slipper and guide, for which specs are available in the shop manual. For the tension slipper, the book spec is a minimum of 3.0 mm. At is thinnest (the middle), I measured 3.64 mm, compared to the ends with a thickness over 5.8 mm. I’m assuming that a new one is uniform in thickness throughout (can someone confirm?), so this piece may be reaching it’s limit and should be replaced. Agreed?
With the cam chain guide, I’m confused by the spec in the book, which is minimum thickness of 5.0 mm. Is this measured at the thinner edges of the guide, or the thicker middle portion that is raised? My measurements were 5.71 mm for the thicker middle section, and 4.23 mm for the thinner sides. Should this be replaced? What are the thickness measurements on a new one?
Finally, A question about the horseshoe cam tensioning lever. There are some photos on this forum showing chain damage to the pivot point, and I have some too as shown here.
Is this amount of damage that bad? What causes this this damage? Is it a cam chain that is not tensioned properly and has too much slack, thus allowing the chain to smack against the lever pivot? The pivot moves readily, so it suspect the previous owner didn’t tension the chain properly. Since this horseshoe lever is a rather expensive part, I’d prefer to not replace it is all that is needed is better attention to tension settings.
So, if I have to replace all these parts, then I have to replace all these parts. If, however, I can save some money and still have a nice runner to have some fun with, that’s good enough for me. What do you all think?
