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Sunnen mandrel compatability

Laverda

Cast Iron
Joined
Mar 24, 2014
Location
Riverside County, CA
I have three old Sunnen hones. Models MA and LBA. They use the obsolete SL series mandrels of which I have many as they can still be found new on ebay for cheap. I will soon need to hone a bunch of connecting rods and wanted to use the appropriate mandrel for the job which is a CR1750 mandrel. The CR mandrels are designed specifically for connecting rods but will they fit an old machine?

I don't have a SL mandrel of the correct size and need to get something that will do the job.
 
Your machine is low on power but the CR1750 will fit and do the job. Even if you had one of the old SL style mandrels in that range it would not work for honing the big end of a rod. After you cut the caps you have a out of round hole that is about on size at the parting edges but under size 90 degrees from the parting edge. Sunnen designed the CR style hone with wide stones and shoes for this purpose. The wide stones and shoes will go over the parting edges and only hone in the under size areas. This way you can make the rod round and on size without blowing over size at the parting edges.

When you get the CR1750 make sure you read the instructions on adjusting the shoes to the curvature of the rod.
 
You can angle cut the caps to pull the sides in slightly but they will still not be perfectly round. Plan on honing two rods at a time to stabilize them on the mandrel as the length to bore ratio sucks with a single rod.
 
These are not split cap plain bearing rods. But are roller bearing rods. The rods come from Carrillo at 46 mm OD and need to be honed to 46.040 mm for bearing clearance. When the engines were new they used slightly undersized 5 mm rollers which are no longer available. So I need to use full size 5 mm rollers. So in inch terms, I need to hone out about .0015" from the big end. As the rods are new, I am not dealing with an out of round condition. Although if using OEM rods that are salvageable they may be a little out of round and will still need the .0015" honed out.

I have been told that the CR1750 is the best choice??????

For those of you riding back in the 1970's and remember these bikes, here is what I am working on.
 

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Taking just .0015" out accurately with a brand new mandrel/shoes/stone would be a challenge. Until everything is broken in, you'll get chatter and a coarse finish. I don't know about these days, but CR mandrels used to come with a truing sleeve, so you could break it in at roughly the diameter the mandrel was designed for. IMO a PL mandrel with a fine stone is a better choice for this app as you are not having to correct any out of round. I often times will finish rods to within .0005" with the CR, then finish with a PL to eliminate any taper and give it a much smoother finish. You can use the more common 3PL mandrel and put just one stone and shoe in it. It takes practice to do a narrow bore but it works great once you get it dialed it.
 
Your still OK with the CR1750 but order a box (2) stones part number Y44A65 stones they will give you a finish in the 10RA range which is what you want for roller bearings. You might also order a ST1700 truing sleeve. The truing sleeve will come smaller and longer than what you need but it is the closes thing Sunnen makes to that size. If you order the truing sleeve you can cut it in half and bore it out to .010" smaller than your finish size. Then use it to radius your stones before honing.

Because you are starting with a round hole you could use a Sunnen 2GP281750WE mandrel and run it with one stone and one shoe. The stones you would want for that mandrel would be P28A65 for a 10RA finish also use the same ST1700 truing sleeve.

Ether system will give you good results.
 
So as to avoid confusion, a PL mandrel is the older automotive part #, P28 is the industrial #. Here is one on ebay that is already set up with 1 shoe/stone. My adding the link didn't work but just type in 2GP281750 and it'll come up.
 
The single stone P type mandrels are high accuracy, the type with tandem stones, are, or a least were called keyway hones in the industrial catalog, those produce good accuracy.
Mandrels need to be trued with a sleeve, to break in new shoes and stones, but also should be on hand to true the shoes and stones as needed during honing the objects.
 
+1 on using a P28 mandrel.

If you use a P28 mandrel you can use different shoes, the manual or tech support will tell you the best material to use. I prefer bronze shoes when I can get them off of ebay.

+1 on using a truing sleeve to true up the shoe and stones. I'd personally make a sleeve that was the exact size you want to hone, a sleeve too small or too large isn't going to give you the best results when truing up the shoe/stones.
 
+1 on using a P28 mandrel.

If you use a P28 mandrel you can use different shoes, the manual or tech support will tell you the best material to use. I prefer bronze shoes when I can get them off of ebay.

+1 on using a truing sleeve to true up the shoe and stones. I'd personally make a sleeve that was the exact size you want to hone, a sleeve too small or too large isn't going to give you the best results when truing up the shoe/stones.

Start with the sleeve .010" under and throw it out when it is .010" over
 








 
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