Would JB-Weld hold in an engine valve guide.

FOMOGO said:
500 degrees is just not going to cut it for a valve guide. in an air cooled engine you will likely see temps double that at the the valve. Mike
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I disagree aluminum heads would be at that temp would be soft an at 1200 would be in a molted state. I would venture to say that the temp would be more around 200 to 300 degrees. But thats just my opinion you maybe want to research the running temp of a cylinder head temps.
 
doc55 said:
I disagree aluminum heads would be at that temp would be soft an at 1200 would be in a molted state. I would venture to say that the temp would be more around 200 to 300 degrees. But thats just my opinion you maybe want to research the running temp of a cylinder head temps.
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Now. I am curious. It would be very easy to find out the temperature of an air cooled aluminum cylinder head with an IR thermometer.
 
Shootymacshootface said:
Now. I am curious. It would be very easy to find out the temperature of an air cooled aluminum cylinder head with an IR thermometer.
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And I will bet you find temps way cooler with an info red temp sensor I'd guess that way would give you a temp of right around 200f while internal I would guess between 200 to 300. Wish I stll had a bike I'd get the info for you.
And I still say use some 620 loctite and it will work just fine. Just be sure to clean parts real good with some good cleaner and if you don't use loctite primer give it a good time to cure and you will be set.
 
As a former racing kart engine builder I can assure you this would be a very bad idea. Here's a few articles for reference, exhaust gas temps for small engines are normally well over 1000 degrees F.

digital.library.unt.edu

Correlation of Exhaust-Valve Temperatures With Engine Operating Conditions and Valve Design in an Air-Cooled Cylinder

"A semiempirical equation correlating exhaust-valve temperatures with engine operating conditions and exhaust-valve design has been developed. The correlation is based on the theory correlating engine and cooling variables developed in a previous NACA report. In addition to the parameters...
digital.library.unt.edu digital.library.unt.edu

EGT vs A/F gauges | EGT Tuning | Exhaust Gas Temperature

Article on EGT vs Air fuel A/F tuning. The differences between them and how to tune a car properly using these sensors to monitor engine parameters.
enginebasics.com

On one of the engines I built we did use a 3M titanium epoxy product on the intake port which would hold up fairly well but this was in an area cooled by the methanol/air mixture flowing through it. The epoxy was replaced every time the engine was rebuilt which was after approximately 12 hours running time. This was an 8hp OHV Briggs & Stratton which was modified to produce over 25hp, I built dozens of modified engines and have seen just about every failure you can imagine....

I did use the Loctite bearing retaining product for loose main bearing pockets and it would work okay for it's intended application but probably half the time it failed and the block would need to be replaced. Side covers with loose bearings were replaced routinely since unlike the blocks there was little to no modification required and they were cheap.

The proper way to do this repair is knurling the guide and peening as suggested above although this may not be successful in the long run. A replacement head should be sourced if the OP wants the engine to be reliable, also failure of this part at high speed could do significant damage beyond the valve in question.

Also he doesn't state if this is the intake or exhaust valve but I would bet it's the latter which will run considerably hotter than the intake.

In my experience guessing doesn't work for engine rebuilding, I've seen similar repairs and can assure you the results are not pretty.


John
 
That looks like a cast iron valve guide, would you consider making an oversize replacement on the lathe? It would be a tight tolerance job, you would need to know the press fit spec or would have to derive a clearance for the mating parts. The guide can be reamed to precision match the valve stem.

Or you could buy a new head and not have to worry about breaking down in a bad spot at sundown while riding your moto.

I wouldn't use any type of glue on this part. A lot of heat is focused on the exhaust valve, which MUST transfer its heat through the guide and into the head for cooling. Glue in the interface between the valve guide and head could affect thermal conductivity in a bad way.
 
Wow - thanks for the responses. I had been looking at this problem for a week and had considered various ways to fix it or replace it and the associated costs.

I don’t know the history of the bike. I rebuilt the carb got it to run, but it blew smoke extremely bad. I assumed the rings were bad. I pulled the head and cylinder. The piston was trashed and the cylinder needs bored. Then I saw the loose valve guide. I was hesitant to start spending money when I hadn’t had a chance to ride or assess the condition of the rest of the engine and bike yet . I did not want to tear down the whole engine if it OK.

I thought of making an oversize guide but then would need to consider the cost of a .218 reamer and having the seat recut if needed.

I called two cycle machine shop and they said they couldn’t repair the head and that it was best to find a new head. Many OEM parts are no longer available. Looked on EBay for a used head. I didn’t see a moderately priced one that looked good, plus I assume the valve seats would need recut or lapped - to mate with my valves ????, more cost.

I thought maybe the "gluing" or staking may not affect the existing valve seating. The valves have two springs. Since the inner spring sits on the flange of the guide, I would think it would help keep it pushed into the hole.

I really like to do projects the best that I can do them, but I told myself (and my girlfriend) that I wasn’t going to "go crazy" on this project and spend any more money than necessary. (That probably won’t happenJ)

Here is what I will do….. I have enjoyed working on the bike and was looking for a project – so I decided that before I spend money on the cylinder and head, I will just go ahead and tear down the whole engine. Hopefully I will be able to spot any potential problems.

Looking on EBay yesterday I found a head - that I had not seen earlier- that included valves (no recut – just lap?). It was listed as “excellent condition” for $29 and $13 shipping. From all the others I seen – this was a steal. For that amount – I’ll take the chance that it is decent and have it on hand . If I decide the bike is too far gone, for my budget, I can resell it.

Thanks guys. All my “car smart” buddies have passed on so I really appreciate you guys for taking the time to share your knowledge and experiences.

Thanks, Jim
 
Rata222 said:
Looking on EBay yesterday I found a head - that I had not seen earlier- that included valves (no recut – just lap?). It was listed as “excellent condition” for $29 and $13 shipping. From all the others I seen – this was a steal. For that amount – I’ll take the chance that it is decent and have it on hand . If I decide the bike is too far gone, for my budget, I can resell it.
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Yea you could probably get by with a shad tree fix although the seating/lapping of the valve to the valve seat would be problematic.

You could always try putting a "wanted to buy" craigslist add as I have had success with that in the past with buying old/vintage metal working equipment as you never know what someone has sitting around that they never though of selling. I put a duplicate post along with a picture of what I want in the "for sale" section and another in the "wanted" section.

Or start calling around to motorcycle shops to see if they might have a junker sitting in the back corner.

I just found the below site via a google search on used honda ct90 parts and they might be a helpful resource for finding what you need.

ct90-ct110.com - ct90 ct110 Resources and Information.

ct90-ct110.com is your first and best source for all of the information you’re looking for. From general topics to more of what you would expect to find here, ct90-ct110.com has it all. We hope you find what you are searching for!
ct90-ct110.com ct90-ct110.com
 
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Glad you found another head because I don't think you'd be able to fix the old one. My experience doesn't include much motorcycle, nor air cooled, but I have worked a lot with high RPM aluminum engines. When a guide starts walking like that, It will wallow out the hole in the head oval and/or tapered. While knurling and loctite might work, it would be holding on by it's fingernails. Assuming that's the exhaust valve, the local temp is going to be quite a long ways up there. I would believe 500+ under load @ 9000 rpm. Thermal expansion and operating near the temp limits of the loctite will likely overwhelm the incomplete / uneven fit. The proper fix is to ream the hole in the head and make an oversized guide to fit. Or replace the head.
 
You are smart to tear the engine all the way down and do it right, there were so many of these bikes made you will be able to source whatever parts are needed and once it's done you won't have to worry about it again.

They are cool machines with lots of "smiles per mile". I had a 1969 model that I rode to work at Apple when I was there 25 years ago, they have a strong cult following so search around on the internet for a forum like this one that covers them. There will be great resources for parts and knowledge far beyond what we can offer.

Cheers,

John
 
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