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Comp: 140, 140, 140, 90

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Bruce V. Avatar
Bruce V. Bruce Varty
Lakewood, WA, USA   USA
Well its apart and am ready to remove the one low piston.
Question # 1, in the Haynes Manual it calls for using Glass Paper to roughen the hard glaze... is that Wet/Dry paper?? Cant find anyone selling Glass Paper.

Question #2, once I have the piston out is there markings on the existing rings to tell me what size they are??


Sales by trade, mechanic is my new vocation!!!!!!!!!!!

I am a bit nervous about this stage in the process,

Thanks
Bruce

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tapkaJohnD Avatar
tapkaJohnD John Davies
Lancaster, Lancashire, UK   GBR
Bruce ,
Not seen this story before, so please explain.
One bore with low compression, do you KNOW its the piston and why?
If the head is off, you can't do an oil test to see if the valves are OK, but a close inspection may tell.

Glaze busting can be done with Wet'n'Dry, but you need small hands! Tools are available, in the form of a Bore Hone - see http://mgaguru.com/mgtech/hydraulics/ht205.htm for an MG article in how to use one - or a Flexhone, aka 'bobblebrush' - see http://www.brushresearch.com/flex-hone-instructions.php - that are far easier.
They are used with an electric drill set to low speed. Well lubricated, you move the tool up and down in the bore. The objective is a criss-cross pattern of light scratches on the wall at 45 degrees to the vertical. to retyain sump oil while the rings bed in.

Ring sizes depend on overbore size. Presume you are not going for a rebore, so standadd size, but if there is any lip at the bore top, make sure you get a top ring that is chamfered.

JOhn

Greg1835 Avatar
Greg1835 Greg S
Rudolph, WI, USA   USA
If you have a block that has been bored oversize, that would be indicated on the piston as either .010" .020" or .030" oversize. You're probably dealing with a std. size bore, but you never know. If you have a ridge at the top, you'd be better off renting a ridge reamer to remove it before reinstalling piston, then you'll be sure not to bugger your top ring. Sounds like you're leaving your crank and other pistons in, so take care to cover up everything down there to keep crap out while honing, reaming and whatever else.

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Lizzard d id
san jose, CA, USA   USA
In reply to # 1537827 by tapkaJohnD Not seen this story before, so please explain.
He just had the head off and had it redone at a machine shop . The head work up'd the compression numbers but didn't fix the one low cylinder . So now he has moved on the redoing the rings .

Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
When you hone the bore (please use a proper hone) it is important to thoroughly clean the bore with soap and water, or perhaps copious amounts of WD40.

This will be messy, protect the journal of the crank when doing this.

Your piston may be marked Std or with an oversize. Failing that you should measure the bore with a bore gauge.

Some piston rings are specifically made for re-fitting into 'old' bores like you have. They are made to Initally bed in quickly and accomodate some irregularities.

Talk to a ring manufacturer such as Hastings. I found them very helpfull when I had to re-ring an engine when the new rings refused to seat.

Lizzard d id
san jose, CA, USA   USA
In reply to # 1537819 by Bruce V. Well its apart and am ready to remove the one low piston.
Cool

In reply to # 1537819 by Bruce V. Question # 1, in the Haynes Manual it calls for using Glass Paper to roughen the hard glaze... is that Wet/Dry paper?? Cant find anyone selling Glass Paper.
It really doesn't matter if it's glass or not . The metal you sand on will not know the difference . Wet and dry is good .

In reply to # 1537819 by Bruce V. Question #2, once I have the piston out is there markings on the existing rings to tell me what size they are??
You could have the piston measured , that will tell you if its standard size or 10 over , or 20 over , etc .

You need to use a ridge reamer if you have any sort of ridge at all . If you have a ridge and you install new rings the new rings will get broken when they encounter the ridge .

Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
In reply to # 1537846 by Lizzard

You need to use a ridge reamer if you have any sort of ridge at all . If you have a ridge and you install new rings the new rings will get broken when they encounter the ridge .


There are special ring sets with a stepped top ring to help avoid this.

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Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
In reply to # 1537852 by Tonyfixit
In reply to # 1537846 by Lizzard

You need to use a ridge reamer if you have any sort of ridge at all . If you have a ridge and you install new rings the new rings will get broken when they encounter the ridge .


There are special ring sets with a stepped top ring to help avoid this.
https://www.hastingspistonrings.com/tech-tips-faqs

Lizzard d id
san jose, CA, USA   USA
In reply to # 1537852 by Tonyfixit
In reply to # 1537846 by Lizzard

You need to use a ridge reamer if you have any sort of ridge at all . If you have a ridge and you install new rings the new rings will get broken when they encounter the ridge .


There are special ring sets with a stepped top ring to help avoid this.
I'd not suggest them .

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Greg1835 Avatar
Greg1835 Greg S
Rudolph, WI, USA   USA
I wouldn't want to take a chance breaking new rings installing them over a ridge.

TheZster Avatar
TheZster Steven Z
SAINT LOUIS, MO, USA   USA
1978 Triumph 1500 "BLK-BRY"
In reply to # 1537857 by Lizzard
In reply to # 1537852 by Tonyfixit
In reply to # 1537846 by Lizzard

You need to use a ridge reamer if you have any sort of ridge at all . If you have a ridge and you install new rings the new rings will get broken when they encounter the ridge .


There are special ring sets with a stepped top ring to help avoid this.
I'd not suggest them .

+1.....

Ridge reamer...... Based on OP's (Bruce) posts - i'm thinking he would have mentioned a ridge by now if it was noticeable...... But it is a point to be checked off the list for this project....

Z

MHKflyer52 Avatar
MHKflyer52 Martin Keller
Ventura, CA, USA   USA
Have you checked the valve seats for that piston. Read you post and you never mentioned if the valves are setting correctly and adjusted correctly. Sometimes a valve with a seat that is not ground correctly will also give you a loss of compression like that. I find it odd that the other three cylinders have the same compression and the one is that low as they the cylinders tend to ware close to the same unless assembled with a bad set of rings or in correct bore diameter for the piston and rings used when reassembled. Measure the piston bores before removing the piston and see if they are the same diameters. Just seems odd that you have the numbers for compression that you have in my humble belief.
Hope this helps.
cool smiley



Martin Keller
Ventura, CA.
1971 Triumph GT6 (A work always in progress.)

TheZster Avatar
TheZster Steven Z
SAINT LOUIS, MO, USA   USA
1978 Triumph 1500 "BLK-BRY"
In reply to # 1537910 by MHKflyer52 Have you checked the valve seats for that piston. Read you post and you never mentioned if the valves are setting correctly and adjusted correctly. Sometimes a valve with a seat that is not ground correctly will also give you a loss of compression like that. I find it odd that the other three cylinders have the same compression and the one is that low as they the cylinders tend to ware close to the same unless assembled with a bad set of rings or in correct bore diameter for the piston and rings used when reassembled. Measure the piston bores before removing the piston and see if they are the same diameters. Just seems odd that you have the numbers for compression that you have in my humble belief.
Hope this helps.
cool smiley

Thread is an extension of an earlier one (version II)..... Head work was just completed by shop..... hence the decision to re-ring...

Z

MHKflyer52 Avatar
MHKflyer52 Martin Keller
Ventura, CA, USA   USA
I would still check the seat of the valves and the valve adjustment. Dose not mean they did it correctly as it sometimes happens. That even makes more sense now knowing that someone worked on the valves and head.
Just a thought and not ment to be argumentative in any way.

cool smiley

Corrected spelling and wording...can not stand when the computer auto inserts what it thinks is correct.



Martin Keller
Ventura, CA.
1971 Triumph GT6 (A work always in progress.)



Edited 1 time(s). Last edit at 2018-06-03 03:50 PM by MHKflyer52.

Lizzard d id
san jose, CA, USA   USA
In reply to # 1537910 by MHKflyer52 Have you checked the valve seats for that piston.
140 - 140 - 140 - 90 / 120-130-120- 90 , after head work numbers / before head work numbers .

https://www.triumphexp.com/phorum/read.php?8,1493057

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