{"product_id":"pop-up-piston-dolmar-ps510-ps5100-ps5105-45mm-high-comp-zr-57q2-z99e","title":"Pop Up Piston Dolmar PS510 PS5100 PS5105 45mm High Comp","description":"\u003cp\u003ePop up piston for the Dolmar PS510, PS5100 and PS5105. 45mm bore, raised crown, higher compression. WHICH PAGE DO YOU WANT? This page is the POP UP piston. The crown is raised, which reduces the combustion chamber volume and raises the compression ratio. It is for someone who is already working on the cylinder and who will measure squish clearance before final assembly. If you are repairing a saw - a scored piston, a straight gas rebuild, a seizure - buy our STANDARD 45mm piston instead. It costs less, it drops straight in, it keeps factory compression, it runs on the same fuel mix the saw already uses, and there is nothing to measure. That is the right part for most people who land on this page. SPECIFICATION Bore - 45mm Displacement of the saw - 50.4cc, about 3.1 cubic inches Crown - raised, pop up MODELS. PS510, PS5100, PS5100 S, PS5105 and PS5105 H. The same machines were sold as DCS5121, DCS510-18, DCS51020 and EA5000P. DO NOT ORDER FOR A 43MM SAW. This body shell was built with two bores - 45mm pistons carry 181 series numbers and 43mm pistons carry 180 series numbers. PS510, PS5100 and PS5105 are 45mm. Some PS460, PS500, PS5000 and PS4600 machines are 43mm. Measure before ordering. MEASURING SQUISH - DO NOT SKIP THIS Squish is the smallest gap between the flat outer rim of the piston crown and the cylinder's squish band when the piston is at top dead centre. To measure it, feed a length of soft solder in through the spark plug hole so it lies across the squish band, turn the engine over slowly by hand through top dead centre, then take the solder out and measure the crushed thickness. Check at more than one point around the bore, because a cylinder is not always even. Too tight and the piston will touch the head once everything is hot and the bearings have taken up their clearance. Too loose and the squish does nothing useful. On a raised crown piston this is a mandatory step, not a refinement. WHAT HIGHER COMPRESSION GIVES YOU, AND WHAT IT DOES NOT What you get - more cylinder pressure, faster combustion, more torque low in the rev range, and a saw that starts noticeably more easily. What you may not get - more peak power. A raised crown changes how the charge moves across the top of the piston, and builders who have run both on stock cylinders frequently report that the flat top piston made the stronger saw even though the pop up made the higher compression number. We would rather say that plainly than sell you a promise. Buy this for compression and easier starting, and for a build you are going to finish properly. IF THE DOME FOULS The easy fix is a thicker base gasket or a shim. Understand what that does first - it raises the cylinder, which retards exhaust and transfer timing together, and that hands back the power the compression gained. If you have access to machining, cutting the squish band or the dome is the better route. Either way, work it out before final assembly rather than after. RUNNING A HIGH COMPRESSION SAW Mix with higher octane gasoline. Cylinder pressure is up and a work saw spends long periods at full throttle under load. Do not lean the high speed setting out chasing revs. Set it on a tachometer, and stay inside the saw's maximum speed. Check the plug and the piston crown after the first few tanks. BEFORE YOU ASSEMBLE Pressure and vacuum test the crankcase. Check the intake boot and both crankshaft seals. Clean both base gasket faces back to bare metal. Check ring end gap in the bore. Fit the circlips with the opening away from the ports and make sure both seat fully.\u003c\/p\u003e\u003cul\u003e\n\u003cli\u003eTHIS IS THE BUILDER'S PISTON - IF YOU ARE JUST REPAIRING A SAW, BUY THE STANDARD ONE - The raised crown reduces combustion chamber volume and raises compression. It is intended for someone already working on the cylinder - porting, cutting the base, or reworking the squish band - who will measure squish clearance before final assembly. For a scored piston or a seized saw you want our STANDARD 45mm piston instead. It is cheaper, it drops straight in, and there is nothing to measure.\u003c\/li\u003e\n\u003cli\u003eYOU MUST MEASURE SQUISH BEFORE YOU CLOSE IT UP - Squish is the gap between the outer rim of the piston crown and the cylinder's squish band at top dead centre. Measure it by crushing soft solder through the plug hole and turning the engine over by hand, checking at several points around the bore. Too tight and the piston contacts the head once it is hot. This is not a step you can skip on a raised crown piston.\u003c\/li\u003e\n\u003cli\u003eWHAT MORE COMPRESSION ACTUALLY BUYS YOU - HONESTLY - Higher cylinder pressure means faster combustion, more torque low down, and noticeably easier starting. What it does not automatically mean is more peak power. A raised crown changes the flow of the charge over the top of the piston, and builders who have run both often find a flat top piston makes the stronger saw on a stock cylinder. Go in expecting compression and easier starting, not a certain power gain.\u003c\/li\u003e\n\u003cli\u003eIF THE DOME DOES NOT CLEAR, THINK BEFORE YOU SHIM - The usual fix for a dome that touches is a thicker base gasket. That raises the cylinder and retards every port timing figure at once, which gives back exactly the power the compression gained. Machining the squish band or the dome is the better answer if you have the means. Either way, decide before you assemble.\u003c\/li\u003e\n\u003cli\u003e45MM, FITS PS510, PS5100 AND PS5105 - 50.4cc, 45mm bore. Also the PS5100 S and PS5105 H, and the matching units sold as DCS5121, DCS510-18, DCS51020 and EA5000P. Do not order for a PS460, PS500, PS5000 or PS4600 without measuring first - several saws in this body shell were built with a 43mm bore. Mix with higher octane gasoline in a high compression build, and set the saw up on a tachometer rather than by ear.\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"Lil Red Barn","offers":[{"title":"Default Title","offer_id":68009662349466,"sku":"ZR-57Q2-Z99E","price":37.95,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0397\/2346\/6909\/files\/61EeGpUWD8L.jpg?v=1793383550","url":"https:\/\/performancesawsupply.com\/products\/pop-up-piston-dolmar-ps510-ps5100-ps5105-45mm-high-comp-zr-57q2-z99e","provider":"Performance Saw Supply","version":"1.0","type":"link"}