Topic: Loose is better than tight…. No sir it’s just loose

[CB750R]

I’ve joined the unfortunate club of motorcycle enthusiasts who have had their engines damaged by the good folks they pay lots of money to do their jobs!

My cylinders came back from the machinist, who I got to bore them out for the 65mm pistons. I showed him the paper and the clearances, and left the paper in the box with the pistons.

I decided to see how things looked and slid a piston in the bore and it was like sliding a hotdog through a culvert! Ok not that bad but I could rock the piston in the bore pretty easily. I have rebuild a couple dirtbikes and put pistons in a couple street bikes and had never seen a piston slide in so easily. I had another machinist measure up the bores and calculate the clearances. And I’ve attached his writing below.

I have a range of 0038-.0041” cylinder bore clearance when the sheet specifies .0025”

I’m pretty steamed about it, as this shop does some really high end work and shouldn’t be this sloppy. I’m working on a solution, but thank goodness I have enough experience to know that didn’t feel right otherwise I would’ve put together a noisy oil burning engine at best.

[HondaMan]

Oh, man, CB750R...I'm really sorry for you! I've had SO many bad ones like that over the years...
If the pistons are forged. they should be 0.0018"-0.0025" clearance.
If they are cast pistons, they should be 0.0008"-0.0012" at that bore size.
I always go to the lower number, myself.

[grcamna2]

Oh, man, CB750R...I'm really sorry for you! I've had SO many bad ones like that over the years...
If the pistons are forged. they should be 0.0018"-0.0025" clearance.
If they are cast pistons, they should be 0.0008"-0.0012" at that bore size.
I always go to the lower number, myself.

I have asked automotive machine shops to bore sets of cylinders for my motorcycles;unfortunately they don't like to give what they consider to be "too tight" of clearances between the fit of the pistons and freshly bored/honed-to-fit cylinders.
1 out of 50 automotive machinists will bore to "only" .001"  .
 I only look for 'powersports machine shops' for doing Japanese motorcycle work now.

I have found an experienced independent powersports machine shop out here who is accustomed to setting things up correctly.    I've slowly been learning to be patient with this machinist because he's very good at setting the finished product to my specification:according to factory specs in the manual.  This particular shop/machinist is in high demand among many motorcyclists
 I asked him to set the finish hone on my previous piston-to-cylinders job to the low end of the scale at .0006" (the variance is .0006-.0018")on one of my Honda engines;it took a good amount of time for break-in on this particular engine and I'm very pleased with the performance of the engine and I expect it to last quite a few thousand miles,even at the high rpms I run it.
When I consider letting another machine shop do the work..  well.,the price to do the job twice/over again and hope it will be done 'to spec' is more than I can afford,especially after the sad first result.
I've been burned plenty on this issue.

[PeWe]

Bad luck with that shop.
0.0025" is generally sloppy clearance but specified for  most of Dynomans JE forged pistons. (0.0635mm)
I saw that Dynoman specified 0.0020" for their 67mm pistons.

Half that clearance too much for Cruzinimage pistons.

Find new sleeves or a complete cylinder will be next step?
Find another shop too.


Skickat från min CPH2581 via Tapatalk

[Tracksnblades1]

Truely disappointing CR..

Seems like most machine shops are stuck with “4 incn bore, forged pistons/water cooled cast iron block” racing clearances for everything.

Having learnt my lessons on old air cooled DT & MX Yamadogs, once youve found a competent machine shop, be loyal to them..Nothing is worse than assembling an old Yamadog’s new top end with clearances exceeding worn out/service limit specs and immediately catching a ring in the exhaust port..

I smiled when I read “hot dog in a culvert” that expression around here is “hot dog down the hallway”.
Primarily used by younger promiscuous males to express the excessive clearances encountered with younger promiscuous females. Speaking only in terms of plumbing and piping parts 😁

I smiled again as I remembered an older gentleman’s advice to us very young boys when overhearing our conversations of the same..😇😁

[Tracksnblades1]

Phenomenal quality control on your pistons..😁

[CB750R]

Phenomenal quality control on your pistons..😁

Ha you spotted that too, I tried mic’ing them at home and I will admit im not skilled enough to use the tools to get accurate enough measurements when down that many decimal places. I couldnt get the same measurement on one piston let alone 4!

Also i gave the original shop some credit, a culvert is smaller than a hallway, it wasnt ‘that’ loose  haha.

[MRieck]

Bad luck with that shop.
0.0025" is generally sloppy clearance but specified for  most of Dynomans JE forged pistons. (0.0635mm)
I saw that Dynoman specified 0.0020" for their 67mm pistons.

Half that clearance too much for Cruzinimage pistons.

Find new sleeves or a complete cylinder will be next step?
Find another shop too.


Skickat från min CPH2581 via Tapatalk

Because of where you measure the skirt on JE's (.5" from bottom of skirt) they come out at .002 when measured at the conventional spot at the bottom of the skirt.
 I ran forged pistons in my billet block at .0012 to .0013
 Company that makes all aluminum Harley cylinders recommends skirt to wall zero clearance.

[CB750R]

Bad luck with that shop.
0.0025" is generally sloppy clearance but specified for  most of Dynomans JE forged pistons. (0.0635mm)
I saw that Dynoman specified 0.0020" for their 67mm pistons.

Half that clearance too much for Cruzinimage pistons.

Find new sleeves or a complete cylinder will be next step?
Find another shop too.


Skickat från min CPH2581 via Tapatalk

Because of where you measure the skirt on JE's (.5" from bottom of skirt) they come out at .002 when measured at the conventional spot at the bottom of the skirt.
 I ran forged pistons in my billet block at .0012 to .0013
 Company that makes all aluminum Harley cylinders recommends skirt to wall zero clearance.

I went to the shop today, unfortunately the owner was out and won’t be back until Monday. I’m hoping to get some money back as I sure don’t want to chance another botched job by him.

Can my nick name be the owner of yet another Cb750 worth more in the parts than I can sell it for?!? Hahaha

[grcamna2]

Bad luck with that shop.
0.0025" is generally sloppy clearance but specified for  most of Dynomans JE forged pistons. (0.0635mm)
I saw that Dynoman specified 0.0020" for their 67mm pistons.

Half that clearance too much for Cruzinimage pistons.

Find new sleeves or a complete cylinder will be next step?
Find another shop too.


Skickat från min CPH2581 via Tapatalk

Because of where you measure the skirt on JE's (.5" from bottom of skirt) they come out at .002 when measured at the conventional spot at the bottom of the skirt.
 I ran forged pistons in my billet block at .0012 to .0013
 Company that makes all aluminum Harley cylinders recommends skirt to wall zero clearance.

I went to the shop today, unfortunately the owner was out and won’t be back until Monday. I’m hoping to get some money back as I sure don’t want to chance another botched job by him.

Can my nick name be the owner of yet another Cb750 worth more in the parts than I can sell it for?!? Hahaha

Which brand 65mm pistons do you have ?

[CB750R]

It’s the dynoman 836cc kit for the F heads. JE pistons. Mike is obviously correct they do measure higher up the skirt.

I went to the shop today to discuss things. Unfortunately the shop owner won’t be back until Monday. My hopes aren’t super high for a positive resolution. I want a refund as I don’t want them to “fix” this. As far as I know 836cc is the limit on stock sleeves. Anyone make a 65.05mm piston? Haha

[newday777]

It’s the dynoman 836cc kit for the F heads. JE pistons. Mike is obviously correct they do measure higher up the skirt.

I went to the shop today to discuss things. Unfortunately the shop owner won’t be back until Monday. My hopes aren’t super high for a positive resolution. I want a refund as I don’t want them to “fix” this. As far as I know 836cc is the limit on stock sleeves. Anyone make a 65.05mm piston? Haha

I think you can possibly get 849cc pistons and rings to work in the stock sleeves (?) Mike? Will those work in the stock sleeves?
Or get new sleeves and rebore correctly. Send your stuff to Mike!

[Tracksnblades1]

It’s the dynoman 836cc kit for the F heads. JE pistons. Mike is obviously correct they do measure higher up the skirt.

I went to the shop today to discuss things. Unfortunately the shop owner won’t be back until Monday. My hopes aren’t super high for a positive resolution. I want a refund as I don’t want them to “fix” this. As far as I know 836cc is the limit on stock sleeves. Anyone make a 65.05mm piston? Haha

CycleX, used to advertise an 850 piston set to renew worn out 836s….
Don’t know if they’re available or not…
I’m pretty sure Wiseco will make what ever you can dream….and pay for….🤔

[grcamna2]

The excellent,reasonable Powersports independent machinist I bring my items to does great work and he's in Loomis,Ca. and he works out of his home shop.
 The thing is he's got a back-log of customers waiting a while for their jobs.
I've been waiting for 3+ months myself.

[scottly]

Find new sleeves or a complete cylinder will be next step?

I would also replace the sleeves; you could probably pick up some used ones for a lot less than a new set of pistons.

[willbird]

some folks I follow on youtube have been using Line2Line coatings on a variety of things including piston skirts. the coating self clearances, not sure if anybody is using it on air cooled engines or not.

looks like it costs $38 per piston for four pistons up to .006”, they can add more at additional cost. the one guy using their stuff ran two 1/8 mile passes with no oil pump belt in a high 5 second low 6 second car and only minor damage to one main bearing. oil pump belt came off due to tire shake, he had not checked the box to shut engine off if there was low oil pressure

https://www.line2linecoatings.com/faqs.html#:~:text=For%20up%20to%20.,006”%20diametric.

[grcamna2]

some folks I follow on youtube have been using Line2Line coatings on a variety of things including piston skirts. the coating self clearances, not sure if anybody is using it on air cooled engines or not.

looks like it costs $38 per piston for four pistons up to .006”, they can add more at additional cost. the one guy using their stuff ran two 1/8 mile passes with no oil pump belt in a high 5 second low 6 second car and only minor damage to one main bearing. oil pump belt came off due to tire shake, he had not checked the box to shut engine off if there was low oil pressure

https://www.line2linecoatings.com/faqs.html#:~:text=For%20up%20to%20.,006”%20diametric.

Great product,from what I can see.

[Tracksnblades1]

Find new sleeves or a complete cylinder will be next step?

I would also replace the sleeves; you could probably pick up some used ones for a lot less than a new set of pistons.

I would follow either of these…anything a size under 836 would work…

[PeWe]

Find new sleeves or a complete cylinder will be next step?

I would also replace the sleeves; you could probably pick up some used ones for a lot less than a new set of pistons.

I would follow either of these…anything a size under 836 would work…

Find another cylinder for the sleeves only.
Cheap one due to fin damages beyond use.
Rusty not cracked stock  bores even cheaper.

Ensure to get right sleeves, early or later for wider oil return holes that includes the sleeves.

[HondaMan]

The 65mm bore size (836cc) has long been considered the limit of boring for the stock sleeves. The fin casting must be bored and thicker sleeves installed for bigger bores.

I once bored to S12 in a set of 250cc Hawk cylinders before I knew about their early limits, which were only supposed to go to S8. They lasted 45 miles before one of the sleeves broke off just below the fins, locking the engine instantly from 55 MPH. Long skid mark...

The machinist I use bores to 0.0015" smaller than the desired final number, then hones to the final number so he doesn't overshoot it. He's got a real nice hone with 8 inserts in it that he replaces often to keep them (and the bores) straight. You cannot insert the piston beyond the ring grooves into the unhoned bore. Not the cheapest shop around, but done correctly: I only get a discount because of how many I bring them every year.

[grcamna2]

The 65mm bore size (836cc) has long been considered the limit of boring for the stock sleeves. The fin casting must be bored and thicker sleeves installed for bigger bores.

I once bored to S12 in a set of 250cc Hawk cylinders before I knew about their early limits, which were only supposed to go to S8. They lasted 45 miles before one of the sleeves broke off just below the fins, locking the engine instantly from 55 MPH. Long skid mark...

The machinist I use bores to 0.0015" smaller than the desired final number, then hones to the final number so he doesn't overshoot it. He's got a real nice hone with 8 inserts in it that he replaces often to keep them (and the bores) straight. You cannot insert the piston beyond the ring grooves into the unhoned bore. Not the cheapest shop around, but done correctly: I only get a discount because of how many I bring them every year.

excellent 

[MRieck]

He isn't going to have a problem....I'm on it fellas. I'd just like to add the Millennium Technologies will bore to spec whether an aluminum cylinder or iron sleeve. They are very good with only 1 F up that I have heard of that they corrected.

[dragracer]

He isn't going to have a problem....I'm on it fellas. I'd just like to add the Millennium Technologies will bore to spec whether an aluminum cylinder or iron sleeve. They are very good with only 1 F up that I have heard of that they corrected.

Glad your assisting in getting this problem ironwd out. I hate when mistakes are made by the "professionals" on such a straightforward task.

[scottly]

He isn't going to have a problem....I'm on it fellas. I'd just like to add the Millennium Technologies will bore to spec whether an aluminum cylinder or iron sleeve. They are very good with only 1 F up that I have heard of that they corrected.

Glad your assisting in getting this problem ironwd out. I hate when mistakes are made by the "professionals" on such a straightforward task.

Mike, do you remember the Cyclex under-cut trans that had the snap-rings installed incorrectly? It's one thing to F up and correct it, and another thing to F up and do nothing to correct it.
"Hey Scott,

Yes, CycleX sent them to me ziptied so nothing came apart and told me it was all set to drop in and assemble to motor.

I took some photos and spoke to Ken on the phone and while he wouldn't outright admit anything, he seemed to suggest that his mechanic "could" have made the mistake of putting the circlip on backwards.

At the end of the day, nothing was done. It's just one of those things you have to accept."
http://forums.sohc4.net/index.php/topic,193043.25.html

[MRieck]

He isn't going to have a problem....I'm on it fellas. I'd just like to add the Millennium Technologies will bore to spec whether an aluminum cylinder or iron sleeve. They are very good with only 1 F up that I have heard of that they corrected.

Glad your assisting in getting this problem ironwd out. I hate when mistakes are made by the "professionals" on such a straightforward task.

Mike, do you remember the Cyclex under-cut trans that had the snap-rings installed incorrectly? It's one thing to F up and correct it, and another thing to F up and do nothing to correct it.
"Hey Scott,

Yes, CycleX sent them to me ziptied so nothing came apart and told me it was all set to drop in and assemble to motor.

I took some photos and spoke to Ken on the phone and while he wouldn't outright admit anything, he seemed to suggest that his mechanic "could" have made the mistake of putting the circlip on backwards.

At the end of the day, nothing was done. It's just one of those things you have to accept."
http://forums.sohc4.net/index.php/topic,193043.25.html

I remember and you are correct about screwing up and doing nothing to correct it. I'm not perfect and have made mistakes.....I have also done my best to rectify the situation. Speaks volumes about CycleX.