Just got bit by the tight cam bearing bug
- Thread starter EngineerDoug
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If you install new cam bearings you might still have a tight fit? There could be some misalignment in the block cam bore? That's no big deal, I'd work with what you have and if you aren't happy with it then change the bearings.
EngineerDoug
Well-Known Member
Hmm, I see evidence of grit left from the scotchbrite. First of all, there are minute scratches on the cam journals. I polished these out and completely bathed the camshaft with hot water & simple green. I also took a clean white cloth and wiped one of the bearings - there remains a grey slurry on the bearings. They are still dirty.
I am going to go the super conservative route and install new bearings. That way I will feel better about really getting the residual abrasive out of the block (I'll use the hot water and simple green again). Installing the bearings was no big deal, and the cost is negligible compared to the risk. I think I will install the front and rear bearings first, and see how the cam spins. Then install bearings one at a time and check for tightness. I suspect the tight spot will be the #3 bearing again, but we'll see.
I did come across a tech note from Mahle on the web, stating that they do not recommend the use of any abrasives to hone tight bearings - scrape them instead. I do appreciate all the tips and different perspectives. I decided to rebuild this engine as a learning experience on a low budget, and I have picked up a lot thus far.
The good news is the crank lays in the block just fine, with all bearing clearances between 0.002" and 0.003". Spins nice and smooth with assembly lube on the bearings.
I am going to go the super conservative route and install new bearings. That way I will feel better about really getting the residual abrasive out of the block (I'll use the hot water and simple green again). Installing the bearings was no big deal, and the cost is negligible compared to the risk. I think I will install the front and rear bearings first, and see how the cam spins. Then install bearings one at a time and check for tightness. I suspect the tight spot will be the #3 bearing again, but we'll see.
I did come across a tech note from Mahle on the web, stating that they do not recommend the use of any abrasives to hone tight bearings - scrape them instead. I do appreciate all the tips and different perspectives. I decided to rebuild this engine as a learning experience on a low budget, and I have picked up a lot thus far.
The good news is the crank lays in the block just fine, with all bearing clearances between 0.002" and 0.003". Spins nice and smooth with assembly lube on the bearings.
I like to hear how things go from posts. If your have a problem and solve it and don't post how the problem was solved nobody learns.
Good luck.
Good luck.
mentor70
Well-Known Member
my block was so bad that when i pulled the cam out, it pulled #2 cam bearing out with the cam!
it happened twice, thats when i took it back to the machine shop and had the cam journals resized.
Duro-bond makes an over sized cam bearing kit.
after i had this done, dropping the cam in was like butter.
i think this is the proper way to do it.
it happened twice, thats when i took it back to the machine shop and had the cam journals resized.
Duro-bond makes an over sized cam bearing kit.
after i had this done, dropping the cam in was like butter.
i think this is the proper way to do it.
dieseldazzle
Well-Known Member
They do make oversized cam bearings but I feel you are obsessing. Put a new set in like you plan, scrape to fit and be done with it
miller
Well-Known Member
Not that it matters, since it would be better being able to see the leftovers from the scotchbrite on the bearings. But, yes, working any part with scotchbrite will leave some of the fibers on the part. Stop right there...fully agree best to just use a bearing scraper to begin with.
I have through the years used scotchbrite on almost every radial/auto bearing I've had to install, unless they were brand new...with never any problems. Though, I'll admit I usually use the stuff 'wet', fine grade, with kerosene.
Lol...sound like a GD scotchbrite sales pitch...huh! Just use what works for you, and get the job done.
I have through the years used scotchbrite on almost every radial/auto bearing I've had to install, unless they were brand new...with never any problems. Though, I'll admit I usually use the stuff 'wet', fine grade, with kerosene.
Lol...sound like a GD scotchbrite sales pitch...huh! Just use what works for you, and get the job done.
Sounds like a real engineer obsessing. No offense, go with Miller and the rest. The best advice I have is #5&4 bearings first off, then 1 at a time to check for binding.
miller
Well-Known Member
Hehe...no offense...been a hard case all my life.
EngineerDoug
Well-Known Member
Guilty as charged....I have been obsessing about this issue. Been an engineer (electrical/communications) for 35 years. Like other skills, I think there is a threshold of intuition/instinct that you acquire with experience. Lacking that, and having never been this deep into a rebuild, I test the ice several times before I take my next step onto the frozen lake. Being OCD and a self-confessed "control enthusiast" doesn't help, either, chuckle, chuckle.
I should have my new bearings today and will indeed put them in the block in stages. I like the idea of cutting the old cam journals to serve as scrapers, and using those to ream the new bearings as needed.
Thanks again.
I should have my new bearings today and will indeed put them in the block in stages. I like the idea of cutting the old cam journals to serve as scrapers, and using those to ream the new bearings as needed.
Thanks again.
Doug it's a tough crowd here.
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I got the tip I mentioned from a trusted machinist.
EngineerDoug
Well-Known Member
Hey guys,
I got all my new cam bearings installed, and sure enough #3 was tight. Took the old cam, cut a groove across the #3 journal, and spun it a couple of times in the block. I also bought a bearing scraper and scraped a few high spots on bearings #1 and #5 because they were easy to reach. Worked like a charm - cam is now installed and spins freely. Re-installed the crank and I am hoping to get my pistons and rods back tomorrow. The short block will soon be done. I am curious to see how far below the deck these pistons really are - I would predict 0.026" or so - this will tell me my static compression. Heads are 90cc, and I want to use the 0.020" steel head gasket.
I feel a lot better about the cam & crank now - thanks again.
I got all my new cam bearings installed, and sure enough #3 was tight. Took the old cam, cut a groove across the #3 journal, and spun it a couple of times in the block. I also bought a bearing scraper and scraped a few high spots on bearings #1 and #5 because they were easy to reach. Worked like a charm - cam is now installed and spins freely. Re-installed the crank and I am hoping to get my pistons and rods back tomorrow. The short block will soon be done. I am curious to see how far below the deck these pistons really are - I would predict 0.026" or so - this will tell me my static compression. Heads are 90cc, and I want to use the 0.020" steel head gasket.
I feel a lot better about the cam & crank now - thanks again.
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