7 replies to this topic

[tobysmini]

hi all

I hope the picture work as I'm not the best at computer's. ok so here's the story.

I brought a rebuilt 1380 nearly two years ago from a reputable engine builder, and it ran great for 1300miles. I wanted to put the engine in another mini and thought I would check/rebuild the head and I found this.    

its hard to see in the pictures. so after seeing this I pulled one of the pistons out to see if there is marks on the piston and check the ring gap. the ring gap on the top ring is 0.014".

the piston pictures didn't come out very well but there is very light straight scratches on the skirt. 

this is the bore from the bottom.

I called the engine builder and emailed pictures to him and he said it'll be fine just put it back together  

but wanted a second opinion.

any help would be great 

thank you

[minimans]

Difficult to tell from those pictures but the bore looks good, vertical scratching is normal as long as they are not deep. What isn't clear is the deposits on the piston and the top edge of the bore? The pistons look to be pockmarked? by burning of the aluminum? Possibly some detonation/pinging going on? 

[Spider]

I'd say it's a bit tight on piston to bore clearance and may not be getting enough Oil splashed up the Bores. There's a number of possible reasons for the latter.

 

Also, the cross-hatch angle of the Honing is way too shallow, it looks to be 10 - 20⁰ and need to be around the 45⁰ mark. The Honing also looks to be way too light on. Both of these may also have something to do with the Bore Lube issue.

 

 

Also, the shot from the crankcase - the Cam Lobe - what's the score on that? Is it worn away or is it just the photo?

[tobysmini]

I'd say it's a bit tight on piston to bore clearance and may not be getting enough Oil splashed up the Bores. There's a number of possible reasons for the latter.

 

Also, the cross-hatch angle of the Honing is way too shallow, it looks to be 10 - 20⁰ and need to be around the 45⁰ mark. The Honing also looks to be way too light on. Both of these may also have something to do with the Bore Lube issue.

 

 

Also, the shot from the crankcase - the Cam Lobe - what's the score on that? Is it worn away or is it just the photo?

 

the cam lobe is just a dodgy picture it looks perfect in person. if the honing is to shallow and wrong angle should I have it rehoned ?

the oil pressure was always good according to the mechanical gauge. is there a way I can increase the amount of oil getting to the piston?

[tobysmini]

Difficult to tell from those pictures but the bore looks good, vertical scratching is normal as long as they are not deep. What isn't clear is the deposits on the piston and the top edge of the bore? The pistons look to be pockmarked? by burning of the aluminum? Possibly some detonation/pinging going on? 

I don't think the scratches are deep as I cant feel them with my nail.

I did have a problem with my megajolt where it retarded the engine around 20degrees for around 10 minutes until it overheated and broke down the triggerwheel boss had snapped could the pockmarks be caused by that?

[tobysmini]

I think the piston is ok and not pockmarked I think it was just dirty I took a pic of it after a clean I'll see if it works.

the scratches on it might be normal I'm not sure.  

[Spider]

 

I'd say it's a bit tight on piston to bore clearance and may not be getting enough Oil splashed up the Bores. There's a number of possible reasons for the latter.

 

Also, the cross-hatch angle of the Honing is way too shallow, it looks to be 10 - 20⁰ and need to be around the 45⁰ mark. The Honing also looks to be way too light on. Both of these may also have something to do with the Bore Lube issue.

 

 

Also, the shot from the crankcase - the Cam Lobe - what's the score on that? Is it worn away or is it just the photo?

 

the cam lobe is just a dodgy picture it looks perfect in person. if the honing is to shallow and wrong angle should I have it rehoned ?

the oil pressure was always good according to the mechanical gauge. is there a way I can increase the amount of oil getting to the piston?

 

 

Got that on the Cam.

 

Just having read you post re: Overheating, this is also a possible cause for the scoring too.

 

I would suggest cleaning up the pistons (the skirts should clean up quite OK), measuring them and the bore. It is likely that you'd be able have it honed - properly - fit new rings and go again.

 

High Oil Pressure is not an indication that Oil is getting splashed up the bores. If the Big End Clearances are too tight, this will reduce the Oil that gets on the Bores and also on to the Cam.

[tobysmini]

 

 

I'd say it's a bit tight on piston to bore clearance and may not be getting enough Oil splashed up the Bores. There's a number of possible reasons for the latter.

 

Also, the cross-hatch angle of the Honing is way too shallow, it looks to be 10 - 20⁰ and need to be around the 45⁰ mark. The Honing also looks to be way too light on. Both of these may also have something to do with the Bore Lube issue.

 

 

Also, the shot from the crankcase - the Cam Lobe - what's the score on that? Is it worn away or is it just the photo?

 

the cam lobe is just a dodgy picture it looks perfect in person. if the honing is to shallow and wrong angle should I have it rehoned ?

the oil pressure was always good according to the mechanical gauge. is there a way I can increase the amount of oil getting to the piston?

 

 

Got that on the Cam.

 

Just having read you post re: Overheating, this is also a possible cause for the scoring too.

 

I would suggest cleaning up the pistons (the skirts should clean up quite OK), measuring them and the bore. It is likely that you'd be able have it honed - properly - fit new rings and go again.

 

High Oil Pressure is not an indication that Oil is getting splashed up the bores. If the Big End Clearances are too tight, this will reduce the Oil that gets on the Bores and also on to the Cam.

 

awesome thank you I will do that

i will also look into ways of increasing the oil to the pistons.