Measuring Cylinder Bore Diameter

[lone wolf]

I think the focus point here has been lost. Two stroke pistons and cylinders are not high tech stuff. As far as performance of engines chainsaws are at the bottom. The chromium plating on a typical cylinder is very thin two to eight thousandth with some exceptions. If the plating is good the cylinder is fine and not out of tolerance. The factory specs On my Ford 460 CI stated if the taper is 9 thousand or less it is in factory specs but I would prefer less. I have a bore gauge that is very precise and expensive but never use and not even sure where it is. If you want to know accurately a bore stick a new or used ring in the bore then square it up with a piston and put your feeler gauge to see what it is then move it to see the difference. Or stick a piston in the bore with a feeler gauge and you will know what needs to be done. Thanks

That makes sense yes.Good post.

 

[sean donato]

My bore gauge is made by fowler. Not high end like the mititoyo guages we had at the machine shop, but works well. I can't honestly say I've ever used it in a saw application, normally for automotive or small 4 stroke rebuilds.

 

[lone wolf]

My bore gauge is made by fowler. Not high end like the mititoyo guages we had at the machine shop, but works well. I can't honestly say I've ever used it in a saw application, normally for automotive or small 4 stroke rebuilds.

Same here used it last on a Kohler 25 hp rebuild.

 

[sean donato]

Bore gauges are not a great tool in that it takes pretty good skill to come up with the exact same measurement every time, ask me how I know. Thanks

I'll bite, how do you know? You set the instrument up in the jig to your desired spec, and go stick it in the bore. If you hit 0 your on spec. It's way more accurate then any snap Guage could dream of being.

 

[Vintage Engine Repairs]

My bore gauge is made by fowler. Not high end like the mititoyo guages we had at the machine shop, but works well. I can't honestly say I've ever used it in a saw application, normally for automotive or small 4 stroke rebuilds.

Thanks Sean, that’s the direction I want to start to head in, 4 stroke engine repair / rebuild and maybe one day, apprentice for a team in drag racing for a season or two - that would be amazing So anything I learn now I hope to be able to use in the future / hobbies / profession. I don’t drink, smoke or do drugs, I work on my business and fiddle with engines. Therefore I don’t mind spending my money on good quality tools. However it seems like, even you guys who work on 4t engines don’t use them much if ever?

 

[Vintage Engine Repairs]

Same here used it last on a Kohler 25 hp rebuild.

In the case of that engine rebuild, would you have been able to get away with -/+ 0.03 mm off spec or was it necessary to be absolutely spot on?

 

[lone wolf]

In the case of that engine rebuild, would you have been able to get away with -/+ 0.03 mm off spec or was it necessary to be absolutely spot on?

Are you working on a Kohler now? IDK I go by the specs they recommend I imagine it would lead to premature wear of rings then piston. Mine was in spec and works fine now.

 

[Vintage Engine Repairs]

Are you working on a Kohler now? IDK I go by the specs they recommend I imagine it would lead to premature wear of rings then piston. Mine was in spec and works fine now.

No no, nothing at the moment, I’m currently scouring Facebook market place for an old Briggs or Honda stationary engine to rebuild and learn on next. i could do another saw, but nothing of interest has come along yet and I really want to learn more / expand my
knowledge on 4 stroke engines.

Something like this:

https://www.facebook.com/marketplace/item/808052896757270/

 

[Ted Jenkins]

I'll bite, how do you know? You set the instrument up in the jig to your desired spec, and go stick it in the bore. If you hit 0 your on spec. It's way more accurate then any snap Guage could dream of being.

I have used my bore gauge several times to find one day one measurement then another a little difference so that tells me it is not easy to get precise reading every time. This matter started out with two stroke out of tolerance two stroke cylinders nothing to do with four strokes which is a whole other matter. Just my take. Thanks

 

[Vintage Engine Repairs]

I have used my bore gauge several times to find one day one measurement then another a little difference so that tells me it is not easy to get precise reading every time. This matter started out with two stroke out of tolerance two stroke cylinders nothing to do with four strokes which is a whole other matter. Just my take. Thanks

Could it be a ambient temperature related? No doubt like anything there is a little skill involved still and accuracy required!

 

[ericm979]

Both the snap and bore gauges require the same technique of rocking the gauge to ensure that you passed square, getting the smallest possible measurement. The snap gauge then also requires you to accurately measure it with the micrometer, while with the bore gauge you're done (hopefully the mechanism does not induce error).
I found the second measuring step with the snap gauges to add a lot of variability. Maybe there's a technique there that I don't know.

But yea modern plated cylinders don't wear like cast iron liners did. You might want to measure other engines but with saws there's not a huge amount of use. You might want it for other engines though. Now, micrometers for pistons on the other hand....

 

[Vintage Engine Repairs]

Both the snap and bore gauges require the same technique of rocking the gauge to ensure that you passed square, getting the smallest possible measurement. The snap gauge then also requires you to accurately measure it with the micrometer, while with the bore gauge you're done (hopefully the mechanism does not induce error).
I found the second measuring step with the snap gauges to add a lot of variability. Maybe there's a technique there that I don't know.

But yea modern plated cylinders don't wear like cast iron liners did. You might want to measure other engines but with saws there's not a huge amount of use. You might want it for other engines though. Now, micrometers for pistons on the other hand....

Thanks Eric, i appreciate your advice. Sounds like both require a degree of care and attention to detail. I am finally getting the hang of the telescoping gauges now. I’ll test a few more things tomorrow and see how I go with it for further consistency. Generally if I’m not bang on, I get within .02mm.

 

[miller755]

I have had no success using these bloody telescoping / snap gauges getting repeatable results until recently.

Maybe the blood on them was affecting the measurement?

I'll see myself out.

 

[Mad Professor]

If you use snap gauges correctly in conjucntion with a very accurate micrometer, to measure the snap gauge, they are pretty good. In particular if the mic is checked with a check block and is the same mic/tool is used to measure a piston or a journal for a clearance.

 

[sean donato]

I have used my bore gauge several times to find one day one measurement then another a little difference so that tells me it is not easy to get precise reading every time. This matter started out with two stroke out of tolerance two stroke cylinders nothing to do with four strokes which is a whole other matter. Just my take. Thanks

Hmm, interesting. The biggest variance I have seen, is if I get in a hurry and don't let a cylinder cool down to ambient temperature. The machine shop was temperature controlled to keep temp out as a variable. Everything got flooded with coolant as well, so less of a heat factor to deal with. Once the set block was set, we would go back and verify the Guage from time to time. Normally wasn't an issue and very repeatable. Interesting gearing about others experiences with them.

 

[Vintage Engine Repairs]

Hmm, interesting. The biggest variance I have seen, is if I get in a hurry and don't let a cylinder cool down to ambient temperature. The machine shop was temperature controlled to keep temp out as a variable. Everything got flooded with coolant as well, so less of a heat factor to deal with. Once the set block was set, we would go back and verify the Guage from time to time. Normally wasn't an issue and very repeatable. Interesting gearing about others experiences with them.

What engines were you working on Sean? I presume not run of the mill car engines..? Do manufactures state a certain dia bore at a certain temp? This is what I feared, how deep do I go with learning how to do it and if you don’t take it to the above degree is it really then worth while doing it at all?

 

[ericm979]

For the motorcycle stuff I was doing there's no temp spec. But I think the assumption is the parts are at room temp which is a fairly narrow range.

 

[sean donato]

Lol

What engines were you working on Sean? I presume not run of the mill car engines..? Do manufactures state a certain dia bore at a certain temp? This is what I feared, how deep do I go with learning how to do it and if you don’t take it to the above degree is it really then worth while doing it at all?

Lol, I was a heavy duty diesel mechanic for a machine shop. We worked mainly on diesels, but basically anything with pistons was fair game. Most of the narcissistic tendencies was from the owner of the company. His theory was you do it once, your do it right, and no comebacks. He was right. No one really crossed trades except the mechanics. The head guy only did head, crank guy, only did cranks and balancing rotating assemblies, block guy just did blocks, even had a rod guy. You had to start in the cleaning department, because you can't rebuild an engine if it isn't clean. Cleaning department did the dry mag particle inspection on blocks and heads, all the shafts were wet magged, by the crank guy. Rods by the rod guy. You get the idea. Learned a lot there.

 

[sean donato]

For the motorcycle stuff I was doing there's no temp spec. But I think the assumption is the parts are at room temp which is a fairly narrow range.

Yep more or less

 

[Vintage Engine Repairs]

I think what I’ll do is continue to practise more with the hateful telescoping gauges on known sizes and if I need measurements which I can’t accuractly achieve with snap gauges I’ll invest into bore gauges. Right now I’m walking a tightrope and my little office / workshop in the 2 bedroom apartment we’re in is slowly spilling out to around the rest of the house, much to the frustration of my partner. I have started to put things in the roof space which she doesn’t know about yet. My single tool box is full and I can only just about get in the office