73 R75/5. Right side valve cover center bolt came out by hand when removing for valve adjustment. Time sert, helicoil, bolt with nut in the recess under the spark plug?? Anyone go down these paths that has input on best fix, love your advice. Also, at TDC ,on BOTH sides , the valves were tight as a drum. I found that very strange. Thanks to Snowbums article that problem is solved. Hoping there's no damage from them being so tight. Thanks in advance, Bruce
Any idea of the mileage on your R75/5? The valve seats on my R75/5 were experiencing accelerated recession/erosion at around 75,000 miles. The clearances would tighten up in less than 500 miles after adjusting. You will want to monitor that situation. The solution that worked for me was a complete valve job with new, OEM, seats and valves and guides. That cost me $900 ten years ago.
Regarding the valve cover stud, if it were my bike, I would use a helicoil.
former Airmarshal, IL.
73 R75/5.
A. Right side valve cover center bolt came out by hand when removing for valve adjustment. Time sert, helicoil, bolt with nut in the recess under the spark plug?? Anyone go down these paths that has input on best fix, love your advice.
B. Also, at TDC ,on BOTH sides , the valves were tight as a drum. I found that very strange. Thanks to Snowbums article that problem is solved. Hoping there's no damage from them being so tight. Thanks in advance, Bruce
A. Look straight down on the cylinder head. You'll see there is a small air-filled void in the cylinder head between the rocker arm chamber and the top of the combustion chamber. The best home repair I've seen is to get a slightly longer stud, drill the existing hole in the cyl head all the way through into that void, then place a suitably ground/shaped/fitted steel hex nut into that void. In this way the stud is pulling on the steel nut and not the soft aluminum threads of the cyl head. You've never noticed that void before, and when the repair is completed you'll never notice the hex nut.
The professional way is to insert a HeliCoil. Due to the length of the HeliCoil tap you may still need to deepen the exiting stud hole as per above. And the cost of the initial kit may be high because of the inclusion of the HeliCoil Tap, Guide and Installer Tool, as well as multiple coils... all to install one HeliCoil.
TIP: One of the big concerns of using either method is keeping the hole square to the work so that the stud also gets re-installed straight. Re-fitting the valve cover before starting will go a long way in guiding the drill bits and taps toward the perfect installation angle. Go slow and use lots of lubricant. The aluminum used on the cylinder heads is soft and 'gummy' and will readily adhere to unlubricated drills and taps.
B. As you rock the flywheel back and forth +/-10° around TDC, you'll see one set of rocker arms moving. In this crankshaft position the opposite cylinder should have slack in both rocker arms. This "slack" is basically the clearance necessary to get motor oil onto the cam lobes before the lift of the cam occurs. Without this "valve clearance" the camshaft and cam followers can experience high rates of wear due to lack of lubrication.
The root cause is the lack of lead in modern fuels. When your bike was new leaded fuels were common. The lead cushioned the valve while landing on the valve seat. Now that all fuels are lead-free that action is not present, and so the valve seat takes a beating. All this hammering erodes the valve seat, which allows the valve to sit deeper and deeper into the cyl head, which then removes the valve clearance as measured at the top of the valve stem. You can check and adjust your valves on a regular basis (approx every 2500 miles), or you can replace all 4 existing valve seats with a harder material.
Oilhead valves get looser; Airhead valves always get tighter.
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Appreciate, as always your help Richard and James. Bike shows 30,000 miles ( or is it 130,000). None knows! Anyway, I think I'll try the method using a nut on the back side of the head. The holes are already completely through on both sides. I just assumed that that was the way they were from the factory. Any idea of a good place to send these heads out if the valve seats are toast? Is there anyway to examine this problem without removing the heads? Also curious if I should press on with a test fire up on this bike or not? Supposedly the bike (engine)was gone over thoroughly by the previous owner, ( now deseased), so I have no way to glean information. Thanks in advance, Bruce.
Appreciate, as always your help Richard and James. Bike shows 30,000 miles ( or is it 130,000). None knows! Anyway, I think I'll try the method using a nut on the back side of the head. The holes are already completely through on both sides. I just assumed that that was the way they were from the factory. Any idea of a good place to send these heads out if the valve seats are toast? Is there anyway to examine this problem without removing the heads? Also curious if I should press on with a test fire up on this bike or not? Supposedly the bike (engine)was gone over thoroughly by the previous owner, (now deceased), so I have no way to glean information. Thanks in advance, Bruce.
• I have never needed the "nut in the void" repair, so I can't tell you which stud is used. It may well be the existing stud, simply set 10mm deeper into the cyl head. Experimenting will help you discover, or maybe a member who has that repair will pop on with the answer.
• This issue should not stop you from starting your bike. Tight valves, in and of itself, does NOT prove anything ! This can easily occur if your valve adjustment procedure is not 100%. So what I'm saying is that we don't disassemble engines on a "hunch". Like a doctor, we allow the patient to go about daily tasks while we keep a careful eye on their progress. So set the clearances correctly, crank and run the engine with the correct fuels and oils, then re-measure the clearances in 1000 miles. THAT will often tell you more than disassembling the engine, because if you simply take the engine apart the wear you may find could have occurred over 40,000 miles. You won't have ANY clue as to the RATE OF WEAR. This because Rate is what you Really want to know. Think of it this way, your doctor wants to know if your deformity occurred over 70 years, or developed within the last 3 months. That's what I mean by Rate.
Your Airmail newsletter is full of accredited valve seat repair houses. The acclaimed leader is Ted Porter at San Jose BMW. Prices are going to vary widely. This work is akin to heart surgery for the human. So you want someone very good at what they do, but you don't necessarily need to be flown to Geneva, Switzerland in a private jet for a stay in a private 5 room hospital just to get a stint. If this work is ever proved necessary, sometimes that work can be done locally for a fraction of the cost with the same great results. A member on this board wrote an article about having this very same done within the last 9 months. Research !
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Thanks Richard. I'll press on with the trial start up
A member on this board wrote an article about having this very same done within the last 9 months. Research !
Hope this helps.
What I meant to tell you was that BOTH subjects "stripped valve cover bolt" and "valve seat replacement" have been covered here on the Airhead forum in-depth.
The Search function on this board isn't much to write home about, so I would suggest using Google to do a forum-wide search. There is a specific wording for that type search (that eludes me at the moment), but I know it can be done.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Bruce, I am going to ask you to check your clearances frequently. If the seats are eroding rapidly, the clearances will tighten up quickly. The exhaust valves particularly so. On my R75/5, the exhaust valve would close to zero clearance in very short mileage. Richard's comment about "rate of wear" is the indicator that reveals an issue with valve seat recession. If you had access to a boroscope, you might try fishing it into the cylinder through the spark plug hole to have a look inside. I have never tried that nor do I own a scope, so I can not comment on what exactly a person might see. Another un-scientific indicator would be length of the tappet adjuster that stands proud of the jam nut.
former Airmarshal, IL.
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