Chrome Bore Out Of Round - Whats Acceptable?...

**Smalltownbassin** · 01-31-2022, 05:25 PM

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It's fine thread. I forgot I bought a circlip install tool too! Everyday is a surprise when your memory is crap lol!

**InjectorService** · 01-31-2022, 09:11 PM

So does this same concept work on any or most motors? I've never seen it done before.

**Smalltownbassin** · 01-31-2022, 09:22 PM

Tbd

**Dave Strong** · 01-31-2022, 09:23 PM

Originally Posted by InjectorService

So does this same concept work on any or most motors? I've never seen it done before.

For aluminum sleeve coated cylinders.

Dave

**InjectorService** · 01-31-2022, 09:32 PM

Thanks, I'll have to give it a go if I come across one like that. I'm assuming the steel bores either don't go out of round as easy, and might also be harder to straighten out?

**Dave Strong** · 01-31-2022, 09:49 PM

Originally Posted by InjectorService

Thanks, I'll have to give it a go if I come across one like that. I'm assuming the steel bores either don't go out of round as easy, and might also be harder to straighten out?

Not going to move a steel cyl with an aluminum tool, just bore it. Nic and chrome plated aluminum can be straightened other wise your paying for plating and an aluminum sleeve. Much highr cost than boring a steel cylinder.

Dave

**Smalltownbassin** · 02-01-2022, 06:08 AM

I was told it's used on steel sleeves. Only intended to move metal a couple grand if needed. I already tried it in a hole and yeas it definitely does work without much effort.

**Chaz** · 02-02-2022, 10:25 AM

Over time, all piston skirts will wear a little, but tend to collapse the skirts more than anything. The added clearance and piston rock that comes with it will unseat the rings on the power stroke and push the piston into the corner on the upstroke.

On a ductile iron (steel sleeve) sleeve the rings will wear the thrust faces on the bore, which is easily measured with a dial bore gauge and can be seen as a ridge at the top. The ridge is usually just on one side. If it goes all the way around the bore .. it's beyond worn out. No amount of "bore jacking" is ever going to make it round again. Besides the block's registers and sleeves OD are round, it would be a mistake to try and get the bores ID round at the expense of the block's integrity.

NIC (sputter disbursement) plated cylinders wind up with a finished wall thickness of .003" to .007" when finished honed to size. They seem to wear "slim to none" over time. However, they do move around with heat cycles, key word .. heat.
Lets take Strongman's .006" out of round. If we try to hone it, by the time we get it round .. we would have broken thru the plating. The only thing we can do is try to push it straight. Aluminum does have some memory, it will go back to round pretty easy. But don't be surprised if you pull the motor back down 10 hours later and find the same cylinders (not hurt) have went back to where you found them. Reverse memory I call it. Best you can do is push it straight, touch it with a deglazing stone and send it again ..

**paradak** · 02-02-2022, 11:48 AM

Thank you to all for the information and advice. My project is a 2.4L 175hp chrome bore engine. I verified chrome with a magnet on all cylinders. It had mildly overheated by the previous owner at idle. I acquired the boat, motor and trailer for only $1800 last august (2021). Thought it would be a good project. I did the usual deferred maintenance items including rebuild carbs, sync and link adjustments, timing, rebuilt the fuel pump, new starter, removed oil injection and idle stabilizer, and new head gaskets and got it running in a test tank. Pumps water well, lower unit oil was clean but I changed it anyway.

The bore straightening tool is only for 2.5L engines. So, I set out yesterday to check the out-of-round and taper. The results are are provided in the image if anyone is interested. After seeing these results, I have a little more confidence that the motor was shut down prior to a catastrophic overheat. I will be taking it on a lake test once the weather warms up a little. I realize this will never be a race motor but if I can get a few years of use out of it I am satisfied. Total investment to-date is $1800+$800 which includes adding an over-temp alarm, a temperature gauge, restoring the water pressure gauge and putting new carpet in the boat.

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**rgsauger** · 02-05-2022, 12:44 AM

Paradak, just for grins, have you run a complete compression test on all cylinder holes? you want to do it with the throttle wide open.

**PanRonnie** · 02-05-2022, 04:38 AM

You have put in the diverters in the cooling channels?

**paradak** · 02-05-2022, 06:23 AM

rgsauger - Thanks for your comment. Yes I did do a compression test with throttle wide open. The numbers are in the chart I posted. Three cylinders at 125psi, two at 110psi with one at 100psi (Cyl 1). The test was done with throttle wide open in neutral (which incidentally is not WOT using the standard controller). Also, the motor was warmed up at the time but not full operating temperature. Interesting that cyl 6 with the highest compression (125) had the apparent 0.006" measurement. I expected Cyl 1 to have the larger clearance. It does start easily but I do hear a little piston slap. Here is a link to it running.

https://www.youtube.com/watch?v=9OFm1PoKGQo

PanRonnie,

What are diverters in the cooling channels? I have not heard of these. Are they critical? This motor is/was stock as far as I can tell.

**paradak** · 02-05-2022, 07:01 AM

PanRonnie,

I found a Scream and Fly post on diverters here. No need to respond.

https://www.screamandfly.com/showthr...ight=diverters

I looked up diverters at the US1 site:

http://www.us1.cc/racingcoolingsystem.html

If I understand it, these are for racing engines. I am not planning any high RPM usage of this motor.

**PanRonnie** · 02-05-2022, 10:19 AM

it,s always a good idea to put those diverters in as they force the water around the cylinders
especially the bottom cylinders could suffer from uneven cooling as the water will take the shortest route
possible giving an out of round cylinder bore

**paradak** · 04-20-2022, 09:38 AM

Took the boat out for the first time on-the-water in March at Lake Mead. First time since I went through the motor and performed the deferred maintenance. It seemed to run great up to 5400 RPM. Great acceleration although given the 19 pitch prop and the power, it could easily pull a 21. Top speed (GPS) was abut 50mph at 5300RPM. Here is a Youtube link to the on-the water test. Water pressure was higher than I am used to with my old 91 2L 150. I saw 20psi at 3K RPM and 30PSI up near 5K RPM. It does have the old style poppet valve (round) which I understand can run higher in pressure compared to the newer "figure 8" poppet. Research I have done indicates I likely put the poppet seal in backwards (bevel opposite the block). I have changed that but have not run it since.

https://www.youtube.com/watch?v=bMPn3Pyzhu4