Saturday, April 5, 2014

Honda DOHC Cam Chain Tension

So, here's something we've never found much information about, either from Honda, or online. Starting in the 1980s, Honda switched design for most of their motorcycles from manual cam chain tensioners to automatic models. Once they went automatic, it became a lot harder to know what was going on with the system when you started to hear cam chain noise. There is good information for some bikes on how to tell with the automatic tensioner, but not much on the DOHC inline fours. How can you tell if your cam chain is stretched? And how can you tell if the tensioner has reached its limit?

Having just successfully diagnosed and fixed this problem on a 1983 Honda CB650sc Nighthawk, here is what we learned:

* The bike in question had approximately 31k miles. There was noticeable, very loud rattle, almost like a buzzing/gurgling sound throughout the rev range. It wasn't bad when the bike was cold, but got much worse as the engine warmed up.

* The stock cam chain has to be broken to remove both the chain itself, and the tensioner. However, both jobs can be done with the engine in frame, and only removing the valve cover.

* The tensioner is known for the spring to become weak and/or fail. Also, the spring and the complete tensioner have both been discontinued by Honda, for the CB650sc and CB550sc models with hydraulic valves.

* It may be possible to remove the tensioner without removing the cams, but certainly very difficult. We had to unbolt both cam sprockets from the cams and then remove the intake cam before there was enough room to remove the tensioner.

* The only solution that doesn't require engine disassembly down to the crankshaft is to break the old cam chain at one link, also break the replacement cam chain at one link, temporarily attach to each other and run the new chain around the crankshaft sprocket by manually turning the engine, then remove the old chain and fasten the new chain with a special cam chain masterlink.

* If done this way, be sure to run the new cam chain through the cam chain tensioner before fixing it with the masterlink, much easier than dealing with the tensioner slipper clips!!!

* We replaced the original cam chain tensioner with a unit from a 1983 CB550sc with 10k miles. The tensioner is the same design for both models as far as we can tell.

As far as measuring cam chain wear, we sadly did not take photos or measurements of the old chain before removing it from the bike. However, here are some photos of a new chain and low-mileage tensioner. Photos are with crankshaft positioned at TDC. Note the following that can be used to measure wear:

* Deflection of the chain is very minimal between the cam sprockets, estimate less than 4mm.

* The tensioner has a rod that runs through a center hole in the fastener plate; the closer this rod gets to the upper hole, the farther out the tensioner is (hence, the closer to its limit). As you can see in the photos, the rod is far below this upper hole in our new setup, estimate approx 10mm gap.




Hope this helps some of you out there, good luck!


Friday, February 14, 2014

Motocicletas de Mexico

Two of us from the shop escaped Pittsburgh winter for a week in Mexico. Tons of people ride tiny (by U.S. standards) motorcycles down there, and we loved it. Here are some photos of some of our favorites. Enjoy!



All the way from D.F. to Yucatan on a 200cc bike!
The ubiquitous Honda Passport

Honda Rebel - At 250cc one of the biggest bikes we saw!

Monday, December 23, 2013

Out Of The Office

It's vacation time here at Slagheap Cycles. The shop will be closed to the public from December 23rd until January 23rd. We will still be available by phone and email if you are interested in scheduling work with us once the shop re-opens. Look forward to some motorcycle-related photos from our various travels soon :)

Sunday, December 15, 2013

Monday, November 4, 2013

Winter Motorcycle Storage

I rode my motorcycle out to Udipi Cafe today for lunch (great dosas!), and nearly lost some fingers to the cold. Unfortunately, it's getting to be that time of year when the bikes have to get put away. On that note, we are offering very affordable motorcycle storage and winterization. Here are the rates:

MOTORCYCLE STORAGE: $30/month
  • Bike will be stored indoors and tarped to protect from dust/dirt
  • Electrical outlets for battery tender (we can provide a tender for $5/month)
  • Bike can be removed and re-stored at anytime, given reasonable notice, no extra charge
  • We will pro-rate your charge if you are ready to ride mid-month
MOTORCYCLE WINTERIZATION: $50 + gasoline
  • Powerwash motorcycle to prep for storage
  • Fill gas tank and fuel system with stabilized gasoline, drain carburetors
  • Fog engine cylinders with oil
  • Remove battery and check condition
  • Lift bike weight off tires and onto blocks
  • Spray metal parts with rust prevention spray
  • Spray plastic and vinyl with preservative spray 
  • Cover motorcycle with breathable cover
MOTORCYCLE SPRING STARTUP: $50 + oil & filter
  • Powerwash motorcycle
  • Replace engine oil and change oil filter
  • Fully charge and reinstall battery
  • Clean & gap spark plugs
  • Inflate and check tire pressure
  • Lubricate and check drivechain
  • Refill fuel system

Sunday, October 6, 2013

Yamaha Valve Shim Replacement Tips

Here are some tips on changing valve shims on a 1990 Yamaha Radian. Enjoy!


Step 1 is removing the valve cover (lots of bolts!) and turning the engine to the correct position to measure the clearance of each shim. Remember to take the spark plugs out to make your life easier, and that only certain valves can be measured in each TDC position. The clearance is .11-.15mm for intake and .16-.20mm for exhaust valves. If any valve is out of clearance, you have to remove the existing shim and measure it, then order the appropriate replacement to get the clearance correct. The really useful tip that we learned in this process (that we will share with you here) is that you have to rotate the gap in the valve lifter...otherwise, it is almost impossible to get the shim out.

Here is a picture of the valve we want to remove the shim from. Notice, the gap in the lifter (outer ring) is far to the left, underneath the cam...that means trouble, since we are trying to take the shim out to the right side. The lifter will have to be rotated before the shim can be removed.

Now we have rotated the lifter gap to the right side - ou can see it in the front right. This will make it easy to get our tweezers in to grab that pesky shim. The important thing to know is that you have to do all this BEFORE you insert your shim tool, as once the tool is in, you can't move the lifter. Also, it has to be done with NO CAM PRESSURE on the lifter...the position of the cam lobe in the above pictures is perfect for having a gap between cam and lifter, but still the cam out of the way enough to get a tool on the lifter to rotate it around. So yeah, just put cam like that!

Okay, now our fancy shim tool is in, we have our super fancy tweezers from wallyworld, and that shim is coming right out... Again, notice the position of the cam lobe in all these pictures - in our experience, this was the ideal position for enough clearance for the lifter and the ability to actually reach the shim easily.

Voila! shim is out, ready for the number on it to be deciphered, compared to the chart in the Yamaha manual, and a proper replacement shim ordered. Contrary to reports, we had no problem with removing all the shims, waiting for the new ones to arrive, and then installing those into the shim-less valve lifters. In other words, you don't need to reinstall the old shims and do one at a time. That would be too painful!

Tuesday, July 9, 2013

Recent Bikes At The Shop

1974 Yamaha TX500 - The Precursor to the XS500, a dual overhead cam 8-valve twin in 1974!
1980 Honda CB900, first year of this bike with the unique hi-low gear dual transmission
1970 Yamaha HT-1, what a cute little 90cc 2-stroke...the perfect around-town classic